auto merge of #11946 : alexcrichton/rust/no-io-error, r=brson

Turns out this was a little more far-reaching than I thought it was.

The first commit is the crux of this stack of commits. The `io::io_error` condition is completely removed and the `read` and `write` methods are altered to return `IoResult<T>`. This turned out to be an incredibly far-reaching change!

Overall, I'm very happy with how this turned out (in addition with the `unused_must_use` lint). I had to almost rewrite the pretty printer in `libsyntax` as well as the the formatting in `librustdoc` (as one would expect). These two modules do *tons* of I/O, and I believe that it's definitely improved.

This pull request also introduces the `if_ok!()` macro for returning-early from something that returns a result. I made quite liberal use of this in mostly the pretty printer and html renderer, and I found its usage generally quite pleasant and convenient to have. I didn't really feel like adding any other macro while I was using it, and I figured that pretty printing could be nicer, but it's nowhere near horrid today.

This may be a controversial issue closing, but I'm going to say it.

Closes #6163

src/compiletest/compiletest.rs

@@ -234,7 +234,13 @@ pub fn run_tests(config: &config) {
     // For context, see #8904
     io::test::raise_fd_limit();
     let res = test::run_tests_console(&opts, tests);
-    if !res { fail!("Some tests failed"); }
+    match res {
+        Ok(true) => {}
+        Ok(false) => fail!("Some tests failed"),
+        Err(e) => {
+            println!("I/O failure during tests: {}", e);
+        }
+    }
 }
 
 pub fn test_opts(config: &config) -> test::TestOpts {
@@ -255,7 +261,7 @@ pub fn make_tests(config: &config) -> ~[test::TestDescAndFn] {
     debug!("making tests from {}",
            config.src_base.display());
     let mut tests = ~[];
-    let dirs = fs::readdir(&config.src_base);
+    let dirs = fs::readdir(&config.src_base).unwrap();
     for file in dirs.iter() {
         let file = file.clone();
         debug!("inspecting file {}", file.display());

src/compiletest/procsrv.rs

@@ -58,9 +58,9 @@ pub fn run(lib_path: &str,
     });
 
     match opt_process {
-        Some(ref mut process) => {
+        Ok(ref mut process) => {
             for input in input.iter() {
-                process.input().write(input.as_bytes());
+                process.input().write(input.as_bytes()).unwrap();
             }
             let run::ProcessOutput { status, output, error } = process.finish_with_output();
 
@@ -70,7 +70,7 @@ pub fn run(lib_path: &str,
                 err: str::from_utf8_owned(error).unwrap()
             })
         },
-        None => None
+        Err(..) => None
     }
 }
 
@@ -90,13 +90,13 @@ pub fn run_background(lib_path: &str,
     });
 
     match opt_process {
-        Some(mut process) => {
+        Ok(mut process) => {
             for input in input.iter() {
-                process.input().write(input.as_bytes());
+                process.input().write(input.as_bytes()).unwrap();
             }
 
             Some(process)
         },
-        None => None
+        Err(..) => None
     }
 }

src/compiletest/runtest.rs

@@ -153,7 +153,7 @@ fn run_pretty_test(config: &config, props: &TestProps, testfile: &Path) {
     let rounds =
         match props.pp_exact { Some(_) => 1, None => 2 };
 
-    let src = File::open(testfile).read_to_end();
+    let src = File::open(testfile).read_to_end().unwrap();
     let src = str::from_utf8_owned(src).unwrap();
     let mut srcs = ~[src];
 
@@ -175,7 +175,7 @@ fn run_pretty_test(config: &config, props: &TestProps, testfile: &Path) {
     let mut expected = match props.pp_exact {
         Some(ref file) => {
             let filepath = testfile.dir_path().join(file);
-            let s = File::open(&filepath).read_to_end();
+            let s = File::open(&filepath).read_to_end().unwrap();
             str::from_utf8_owned(s).unwrap()
           }
           None => { srcs[srcs.len() - 2u].clone() }
@@ -318,8 +318,10 @@ fn run_debuginfo_test(config: &config, props: &TestProps, testfile: &Path) {
                 //waiting 1 second for gdbserver start
                 timer::sleep(1000);
                 let result = task::try(proc() {
-                    tcp::TcpStream::connect(
-                        SocketAddr { ip: Ipv4Addr(127, 0, 0, 1), port: 5039 });
+                    tcp::TcpStream::connect(SocketAddr {
+                        ip: Ipv4Addr(127, 0, 0, 1),
+                        port: 5039,
+                    }).unwrap();
                 });
                 if result.is_err() {
                     continue;
@@ -361,7 +363,7 @@ fn run_debuginfo_test(config: &config, props: &TestProps, testfile: &Path) {
                                stdout: out,
                                stderr: err,
                                cmdline: cmdline};
-            process.force_destroy();
+            process.force_destroy().unwrap();
         }
 
         _=> {
@@ -727,7 +729,7 @@ fn compose_and_run_compiler(
 
 fn ensure_dir(path: &Path) {
     if path.is_dir() { return; }
-    fs::mkdir(path, io::UserRWX);
+    fs::mkdir(path, io::UserRWX).unwrap();
 }
 
 fn compose_and_run(config: &config, testfile: &Path,
@@ -852,7 +854,7 @@ fn dump_output(config: &config, testfile: &Path, out: &str, err: &str) {
 fn dump_output_file(config: &config, testfile: &Path,
                     out: &str, extension: &str) {
     let outfile = make_out_name(config, testfile, extension);
-    File::create(&outfile).write(out.as_bytes());
+    File::create(&outfile).write(out.as_bytes()).unwrap();
 }
 
 fn make_out_name(config: &config, testfile: &Path, extension: &str) -> Path {
@@ -1003,7 +1005,7 @@ fn _arm_exec_compiled_test(config: &config, props: &TestProps,
 fn _arm_push_aux_shared_library(config: &config, testfile: &Path) {
     let tdir = aux_output_dir_name(config, testfile);
 
-    let dirs = fs::readdir(&tdir);
+    let dirs = fs::readdir(&tdir).unwrap();
     for file in dirs.iter() {
         if file.extension_str() == Some("so") {
             // FIXME (#9639): This needs to handle non-utf8 paths
@@ -1099,7 +1101,7 @@ fn disassemble_extract(config: &config, _props: &TestProps,
 
 
 fn count_extracted_lines(p: &Path) -> uint {
-    let x = File::open(&p.with_extension("ll")).read_to_end();
+    let x = File::open(&p.with_extension("ll")).read_to_end().unwrap();
     let x = str::from_utf8_owned(x).unwrap();
     x.lines().len()
 }

src/doc/guide-conditions.md

@@ -47,7 +47,7 @@ An example program that does this task reads like this:
 # #[allow(unused_imports)];
 use std::io::{BufferedReader, File};
 # mod BufferedReader {
-#     use std::io::File;
+#     use std::io::{File, IoResult};
 #     use std::io::MemReader;
 #     use std::io::BufferedReader;
 #     static s : &'static [u8] = bytes!("1 2\n\
@@ -55,7 +55,7 @@ use std::io::{BufferedReader, File};
 #                                        789 123\n\
 #                                        45 67\n\
 #                                        ");
-#     pub fn new(_inner: Option<File>) -> BufferedReader<MemReader> {
+#     pub fn new(_inner: IoResult<File>) -> BufferedReader<MemReader> {
 #           BufferedReader::new(MemReader::new(s.to_owned()))
 #     }
 # }
@@ -71,7 +71,6 @@ fn read_int_pairs() -> ~[(int,int)] {
     let mut pairs = ~[];
 
     // Path takes a generic by-value, rather than by reference
-#    let _g = std::io::ignore_io_error();
     let path = Path::new(&"foo.txt");
     let mut reader = BufferedReader::new(File::open(&path));
 
@@ -245,7 +244,7 @@ and trapping its exit status using `task::try`:
 use std::io::{BufferedReader, File};
 use std::task;
 # mod BufferedReader {
-#     use std::io::File;
+#     use std::io::{File, IoResult};
 #     use std::io::MemReader;
 #     use std::io::BufferedReader;
 #     static s : &'static [u8] = bytes!("1 2\n\
@@ -253,7 +252,7 @@ use std::task;
 #                                        789 123\n\
 #                                        45 67\n\
 #                                        ");
-#     pub fn new(_inner: Option<File>) -> BufferedReader<MemReader> {
+#     pub fn new(_inner: IoResult<File>) -> BufferedReader<MemReader> {
 #           BufferedReader::new(MemReader::new(s.to_owned()))
 #     }
 # }
@@ -277,7 +276,6 @@ fn main() {
 
 fn read_int_pairs() -> ~[(int,int)] {
     let mut pairs = ~[];
-#    let _g = std::io::ignore_io_error();
     let path = Path::new(&"foo.txt");
 
     let mut reader = BufferedReader::new(File::open(&path));
@@ -347,7 +345,7 @@ but similarly clear as the version that used `fail!` in the logic where the erro
 # #[allow(unused_imports)];
 use std::io::{BufferedReader, File};
 # mod BufferedReader {
-#     use std::io::File;
+#     use std::io::{File, IoResult};
 #     use std::io::MemReader;
 #     use std::io::BufferedReader;
 #     static s : &'static [u8] = bytes!("1 2\n\
@@ -355,7 +353,7 @@ use std::io::{BufferedReader, File};
 #                                        789 123\n\
 #                                        45 67\n\
 #                                        ");
-#     pub fn new(_inner: Option<File>) -> BufferedReader<MemReader> {
+#     pub fn new(_inner: IoResult<File>) -> BufferedReader<MemReader> {
 #           BufferedReader::new(MemReader::new(s.to_owned()))
 #     }
 # }
@@ -374,7 +372,6 @@ fn main() {
 
 fn read_int_pairs() -> ~[(int,int)] {
     let mut pairs = ~[];
-#    let _g = std::io::ignore_io_error();
     let path = Path::new(&"foo.txt");
 
     let mut reader = BufferedReader::new(File::open(&path));
@@ -415,7 +412,7 @@ and replaces bad input lines with the pair `(-1,-1)`:
 # #[allow(unused_imports)];
 use std::io::{BufferedReader, File};
 # mod BufferedReader {
-#     use std::io::File;
+#     use std::io::{File, IoResult};
 #     use std::io::MemReader;
 #     use std::io::BufferedReader;
 #     static s : &'static [u8] = bytes!("1 2\n\
@@ -423,7 +420,7 @@ use std::io::{BufferedReader, File};
 #                                        789 123\n\
 #                                        45 67\n\
 #                                        ");
-#     pub fn new(_inner: Option<File>) -> BufferedReader<MemReader> {
+#     pub fn new(_inner: IoResult<File>) -> BufferedReader<MemReader> {
 #           BufferedReader::new(MemReader::new(s.to_owned()))
 #     }
 # }
@@ -447,7 +444,6 @@ fn main() {
 
 fn read_int_pairs() -> ~[(int,int)] {
     let mut pairs = ~[];
-#    let _g = std::io::ignore_io_error();
     let path = Path::new(&"foo.txt");
 
     let mut reader = BufferedReader::new(File::open(&path));
@@ -489,7 +485,7 @@ Changing the condition's return type from `(int,int)` to `Option<(int,int)>` wil
 # #[allow(unused_imports)];
 use std::io::{BufferedReader, File};
 # mod BufferedReader {
-#     use std::io::File;
+#     use std::io::{IoResult, File};
 #     use std::io::MemReader;
 #     use std::io::BufferedReader;
 #     static s : &'static [u8] = bytes!("1 2\n\
@@ -497,7 +493,7 @@ use std::io::{BufferedReader, File};
 #                                        789 123\n\
 #                                        45 67\n\
 #                                        ");
-#     pub fn new(_inner: Option<File>) -> BufferedReader<MemReader> {
+#     pub fn new(_inner: IoResult<File>) -> BufferedReader<MemReader> {
 #           BufferedReader::new(MemReader::new(s.to_owned()))
 #     }
 # }
@@ -522,7 +518,6 @@ fn main() {
 
 fn read_int_pairs() -> ~[(int,int)] {
     let mut pairs = ~[];
-#    let _g = std::io::ignore_io_error();
     let path = Path::new(&"foo.txt");
 
     let mut reader = BufferedReader::new(File::open(&path));
@@ -573,7 +568,7 @@ This can be encoded in the handler API by introducing a helper type: `enum Malfo
 # #[allow(unused_imports)];
 use std::io::{BufferedReader, File};
 # mod BufferedReader {
-#     use std::io::File;
+#     use std::io::{File, IoResult};
 #     use std::io::MemReader;
 #     use std::io::BufferedReader;
 #     static s : &'static [u8] = bytes!("1 2\n\
@@ -581,7 +576,7 @@ use std::io::{BufferedReader, File};
 #                                        789 123\n\
 #                                        45 67\n\
 #                                        ");
-#     pub fn new(_inner: Option<File>) -> BufferedReader<MemReader> {
+#     pub fn new(_inner: IoResult<File>) -> BufferedReader<MemReader> {
 #           BufferedReader::new(MemReader::new(s.to_owned()))
 #     }
 # }
@@ -615,7 +610,6 @@ fn main() {
 
 fn read_int_pairs() -> ~[(int,int)] {
     let mut pairs = ~[];
-#    let _g = std::io::ignore_io_error();
     let path = Path::new(&"foo.txt");
 
     let mut reader = BufferedReader::new(File::open(&path));
@@ -696,7 +690,7 @@ a second condition and a helper function will suffice:
 # #[allow(unused_imports)];
 use std::io::{BufferedReader, File};
 # mod BufferedReader {
-#     use std::io::File;
+#     use std::io::{File, IoResult};
 #     use std::io::MemReader;
 #     use std::io::BufferedReader;
 #     static s : &'static [u8] = bytes!("1 2\n\
@@ -704,7 +698,7 @@ use std::io::{BufferedReader, File};
 #                                        789 123\n\
 #                                        45 67\n\
 #                                        ");
-#     pub fn new(_inner: Option<File>) -> BufferedReader<MemReader> {
+#     pub fn new(_inner: IoResult<File>) -> BufferedReader<MemReader> {
 #           BufferedReader::new(MemReader::new(s.to_owned()))
 #     }
 # }
@@ -752,7 +746,6 @@ fn parse_int(x: &str) -> int {
 
 fn read_int_pairs() -> ~[(int,int)] {
     let mut pairs = ~[];
-#    let _g = std::io::ignore_io_error();
     let path = Path::new(&"foo.txt");
 
     let mut reader = BufferedReader::new(File::open(&path));

src/etc/combine-tests.py

@@ -69,6 +69,7 @@ extern mod run_pass_stage2;
 use run_pass_stage2::*;
 use std::io;
 use std::io::Writer;
+#[allow(warnings)]
 fn main() {
     let mut out = io::stdout();
 """

src/libextra/arc.rs

@@ -637,7 +637,7 @@ mod tests {
     fn test_mutex_arc_poison() {
         let arc = ~MutexArc::new(1);
         let arc2 = ~arc.clone();
-        task::try(proc() {
+        let _ = task::try(proc() {
             arc2.access(|one| {
                 assert_eq!(*one, 2);
             })
@@ -668,7 +668,7 @@ mod tests {
     fn test_mutex_arc_access_in_unwind() {
         let arc = MutexArc::new(1i);
         let arc2 = arc.clone();
-        task::try::<()>(proc() {
+        let _ = task::try::<()>(proc() {
             struct Unwinder {
                 i: MutexArc<int>
             }
@@ -687,7 +687,7 @@ mod tests {
     fn test_rw_arc_poison_wr() {
         let arc = RWArc::new(1);
         let arc2 = arc.clone();
-        task::try(proc() {
+        let _ = task::try(proc() {
             arc2.write(|one| {
                 assert_eq!(*one, 2);
             })
@@ -701,7 +701,7 @@ mod tests {
     fn test_rw_arc_poison_ww() {
         let arc = RWArc::new(1);
         let arc2 = arc.clone();
-        task::try(proc() {
+        let _ = task::try(proc() {
             arc2.write(|one| {
                 assert_eq!(*one, 2);
             })
@@ -714,7 +714,7 @@ mod tests {
     fn test_rw_arc_poison_dw() {
         let arc = RWArc::new(1);
         let arc2 = arc.clone();
-        task::try(proc() {
+        let _ = task::try(proc() {
             arc2.write_downgrade(|mut write_mode| {
                 write_mode.write(|one| {
                     assert_eq!(*one, 2);
@@ -729,7 +729,7 @@ mod tests {
     fn test_rw_arc_no_poison_rr() {
         let arc = RWArc::new(1);
         let arc2 = arc.clone();
-        task::try(proc() {
+        let _ = task::try(proc() {
             arc2.read(|one| {
                 assert_eq!(*one, 2);
             })
@@ -742,7 +742,7 @@ mod tests {
     fn test_rw_arc_no_poison_rw() {
         let arc = RWArc::new(1);
         let arc2 = arc.clone();
-        task::try(proc() {
+        let _ = task::try(proc() {
             arc2.read(|one| {
                 assert_eq!(*one, 2);
             })
@@ -755,7 +755,7 @@ mod tests {
     fn test_rw_arc_no_poison_dr() {
         let arc = RWArc::new(1);
         let arc2 = arc.clone();
-        task::try(proc() {
+        let _ = task::try(proc() {
             arc2.write_downgrade(|write_mode| {
                 let read_mode = arc2.downgrade(write_mode);
                 read_mode.read(|one| {
@@ -800,7 +800,7 @@ mod tests {
 
         // Wait for children to pass their asserts
         for r in children.mut_iter() {
-            r.recv();
+            let _ = r.recv();
         }
 
         // Wait for writer to finish
@@ -814,7 +814,7 @@ mod tests {
     fn test_rw_arc_access_in_unwind() {
         let arc = RWArc::new(1i);
         let arc2 = arc.clone();
-        task::try::<()>(proc() {
+        let _ = task::try::<()>(proc() {
             struct Unwinder {
                 i: RWArc<int>
             }

src/libextra/base64.rs

@@ -359,7 +359,7 @@ mod test {
                  ウヰノオクヤマ ケフコエテ アサキユメミシ ヱヒモセスン";
         let b = s.as_bytes().to_base64(STANDARD);
         bh.iter(|| {
-            b.from_base64();
+            b.from_base64().unwrap();
         });
         bh.bytes = b.len() as u64;
     }

src/libextra/ebml.rs

@@ -12,6 +12,10 @@
 
 use std::str;
 
+macro_rules! if_ok( ($e:expr) => (
+    match $e { Ok(e) => e, Err(e) => { self.last_error = Err(e); return } }
+) )
+
 // Simple Extensible Binary Markup Language (ebml) reader and writer on a
 // cursor model. See the specification here:
 //     http://www.matroska.org/technical/specs/rfc/index.html
@@ -595,9 +599,15 @@ pub mod writer {
 
     // ebml writing
     pub struct Encoder<'a> {
-        // FIXME(#5665): this should take a trait object
+        // FIXME(#5665): this should take a trait object. Note that if you
+        //               delete this comment you should consider removing the
+        //               unwrap()'s below of the results of the calls to
+        //               write(). We're guaranteed that writing into a MemWriter
+        //               won't fail, but this is not true for all I/O streams in
+        //               general.
         writer: &'a mut MemWriter,
         priv size_positions: ~[uint],
+        last_error: io::IoResult<()>,
     }
 
     fn write_sized_vuint(w: &mut MemWriter, n: uint, size: uint) {
@@ -609,7 +619,7 @@ pub mod writer {
             4u => w.write(&[0x10u8 | ((n >> 24_u) as u8), (n >> 16_u) as u8,
                             (n >> 8_u) as u8, n as u8]),
             _ => fail!("vint to write too big: {}", n)
-        };
+        }.unwrap()
     }
 
     fn write_vuint(w: &mut MemWriter, n: uint) {
@@ -624,7 +634,8 @@ pub mod writer {
         let size_positions: ~[uint] = ~[];
         Encoder {
             writer: w,
-            size_positions: size_positions
+            size_positions: size_positions,
+            last_error: Ok(()),
         }
     }
 
@@ -635,6 +646,7 @@ pub mod writer {
             Encoder {
                 writer: cast::transmute_copy(&self.writer),
                 size_positions: self.size_positions.clone(),
+                last_error: Ok(()),
             }
         }
 
@@ -645,18 +657,18 @@ pub mod writer {
             write_vuint(self.writer, tag_id);
 
             // Write a placeholder four-byte size.
-            self.size_positions.push(self.writer.tell() as uint);
+            self.size_positions.push(if_ok!(self.writer.tell()) as uint);
             let zeroes: &[u8] = &[0u8, 0u8, 0u8, 0u8];
-            self.writer.write(zeroes);
+            if_ok!(self.writer.write(zeroes));
         }
 
         pub fn end_tag(&mut self) {
             let last_size_pos = self.size_positions.pop().unwrap();
-            let cur_pos = self.writer.tell();
-            self.writer.seek(last_size_pos as i64, io::SeekSet);
+            let cur_pos = if_ok!(self.writer.tell());
+            if_ok!(self.writer.seek(last_size_pos as i64, io::SeekSet));
             let size = (cur_pos as uint - last_size_pos - 4);
             write_sized_vuint(self.writer, size, 4u);
-            self.writer.seek(cur_pos as i64, io::SeekSet);
+            if_ok!(self.writer.seek(cur_pos as i64, io::SeekSet));
 
             debug!("End tag (size = {})", size);
         }
@@ -670,7 +682,7 @@ pub mod writer {
         pub fn wr_tagged_bytes(&mut self, tag_id: uint, b: &[u8]) {
             write_vuint(self.writer, tag_id);
             write_vuint(self.writer, b.len());
-            self.writer.write(b);
+            self.writer.write(b).unwrap();
         }
 
         pub fn wr_tagged_u64(&mut self, tag_id: uint, v: u64) {
@@ -723,12 +735,12 @@ pub mod writer {
 
         pub fn wr_bytes(&mut self, b: &[u8]) {
             debug!("Write {} bytes", b.len());
-            self.writer.write(b);
+            self.writer.write(b).unwrap();
         }
 
         pub fn wr_str(&mut self, s: &str) {
             debug!("Write str: {}", s);
-            self.writer.write(s.as_bytes());
+            self.writer.write(s.as_bytes()).unwrap();
         }
     }
 

src/libextra/hex.rs

@@ -201,7 +201,7 @@ mod tests {
                  ウヰノオクヤマ ケフコエテ アサキユメミシ ヱヒモセスン";
         let b = s.as_bytes().to_hex();
         bh.iter(|| {
-            b.from_hex();
+            b.from_hex().unwrap();
         });
         bh.bytes = b.len() as u64;
     }

src/libextra/json.rs

@@ -234,6 +234,10 @@ use serialize::Encodable;
 use serialize;
 use treemap::TreeMap;
 
+macro_rules! if_ok( ($e:expr) => (
+    match $e { Ok(e) => e, Err(e) => { self.error = Err(e); return } }
+) )
+
 /// Represents a json value
 #[deriving(Clone, Eq)]
 pub enum Json {
@@ -260,6 +264,14 @@ pub struct Error {
     priv msg: ~str,
 }
 
+fn io_error_to_error(io: io::IoError) -> Error {
+    Error {
+        line: 0,
+        col: 0,
+        msg: format!("io error: {}", io)
+    }
+}
+
 fn escape_str(s: &str) -> ~str {
     let mut escaped = ~"\"";
     for c in s.chars() {
@@ -289,13 +301,14 @@ fn spaces(n: uint) -> ~str {
 /// A structure for implementing serialization to JSON.
 pub struct Encoder<'a> {
     priv wr: &'a mut io::Writer,
+    priv error: io::IoResult<()>,
 }
 
 impl<'a> Encoder<'a> {
     /// Creates a new JSON encoder whose output will be written to the writer
     /// specified.
     pub fn new<'a>(wr: &'a mut io::Writer) -> Encoder<'a> {
-        Encoder { wr: wr }
+        Encoder { wr: wr, error: Ok(()) }
     }
 
     /// Encode the specified struct into a json [u8]
@@ -317,7 +330,7 @@ impl<'a> Encoder<'a> {
 }
 
 impl<'a> serialize::Encoder for Encoder<'a> {
-    fn emit_nil(&mut self) { write!(self.wr, "null") }
+    fn emit_nil(&mut self) { if_ok!(write!(self.wr, "null")) }
 
     fn emit_uint(&mut self, v: uint) { self.emit_f64(v as f64); }
     fn emit_u64(&mut self, v: u64) { self.emit_f64(v as f64); }
@@ -333,20 +346,20 @@ impl<'a> serialize::Encoder for Encoder<'a> {
 
     fn emit_bool(&mut self, v: bool) {
         if v {
-            write!(self.wr, "true");
+            if_ok!(write!(self.wr, "true"));
         } else {
-            write!(self.wr, "false");
+            if_ok!(write!(self.wr, "false"));
         }
     }
 
     fn emit_f64(&mut self, v: f64) {
-        write!(self.wr, "{}", f64::to_str_digits(v, 6u))
+        if_ok!(write!(self.wr, "{}", f64::to_str_digits(v, 6u)))
     }
     fn emit_f32(&mut self, v: f32) { self.emit_f64(v as f64); }
 
     fn emit_char(&mut self, v: char) { self.emit_str(str::from_char(v)) }
     fn emit_str(&mut self, v: &str) {
-        write!(self.wr, "{}", escape_str(v))
+        if_ok!(write!(self.wr, "{}", escape_str(v)))
     }
 
     fn emit_enum(&mut self, _name: &str, f: |&mut Encoder<'a>|) { f(self) }
@@ -360,19 +373,19 @@ impl<'a> serialize::Encoder for Encoder<'a> {
         // Bunny => "Bunny"
         // Kangaroo(34,"William") => {"variant": "Kangaroo", "fields": [34,"William"]}
         if cnt == 0 {
-            write!(self.wr, "{}", escape_str(name));
+            if_ok!(write!(self.wr, "{}", escape_str(name)));
         } else {
-            write!(self.wr, "\\{\"variant\":");
-            write!(self.wr, "{}", escape_str(name));
-            write!(self.wr, ",\"fields\":[");
+            if_ok!(write!(self.wr, "\\{\"variant\":"));
+            if_ok!(write!(self.wr, "{}", escape_str(name)));
+            if_ok!(write!(self.wr, ",\"fields\":["));
             f(self);
-            write!(self.wr, "]\\}");
+            if_ok!(write!(self.wr, "]\\}"));
         }
     }
 
     fn emit_enum_variant_arg(&mut self, idx: uint, f: |&mut Encoder<'a>|) {
         if idx != 0 {
-            write!(self.wr, ",");
+            if_ok!(write!(self.wr, ","));
         }
         f(self);
     }
@@ -393,17 +406,17 @@ impl<'a> serialize::Encoder for Encoder<'a> {
     }
 
     fn emit_struct(&mut self, _: &str, _: uint, f: |&mut Encoder<'a>|) {
-        write!(self.wr, r"\{");
+        if_ok!(write!(self.wr, r"\{"));
         f(self);
-        write!(self.wr, r"\}");
+        if_ok!(write!(self.wr, r"\}"));
     }
 
     fn emit_struct_field(&mut self,
                          name: &str,
                          idx: uint,
                          f: |&mut Encoder<'a>|) {
-        if idx != 0 { write!(self.wr, ",") }
-        write!(self.wr, "{}:", escape_str(name));
+        if idx != 0 { if_ok!(write!(self.wr, ",")) }
+        if_ok!(write!(self.wr, "{}:", escape_str(name)));
         f(self);
     }
 
@@ -429,31 +442,31 @@ impl<'a> serialize::Encoder for Encoder<'a> {
     fn emit_option_some(&mut self, f: |&mut Encoder<'a>|) { f(self); }
 
     fn emit_seq(&mut self, _len: uint, f: |&mut Encoder<'a>|) {
-        write!(self.wr, "[");
+        if_ok!(write!(self.wr, "["));
         f(self);
-        write!(self.wr, "]");
+        if_ok!(write!(self.wr, "]"));
     }
 
     fn emit_seq_elt(&mut self, idx: uint, f: |&mut Encoder<'a>|) {
         if idx != 0 {
-            write!(self.wr, ",");
+            if_ok!(write!(self.wr, ","));
         }
         f(self)
     }
 
     fn emit_map(&mut self, _len: uint, f: |&mut Encoder<'a>|) {
-        write!(self.wr, r"\{");
+        if_ok!(write!(self.wr, r"\{"));
         f(self);
-        write!(self.wr, r"\}");
+        if_ok!(write!(self.wr, r"\}"));
     }
 
     fn emit_map_elt_key(&mut self, idx: uint, f: |&mut Encoder<'a>|) {
-        if idx != 0 { write!(self.wr, ",") }
+        if idx != 0 { if_ok!(write!(self.wr, ",")) }
         f(self)
     }
 
     fn emit_map_elt_val(&mut self, _idx: uint, f: |&mut Encoder<'a>|) {
-        write!(self.wr, ":");
+        if_ok!(write!(self.wr, ":"));
         f(self)
     }
 }
@@ -463,6 +476,7 @@ impl<'a> serialize::Encoder for Encoder<'a> {
 pub struct PrettyEncoder<'a> {
     priv wr: &'a mut io::Writer,
     priv indent: uint,
+    priv error: io::IoResult<()>,
 }
 
 impl<'a> PrettyEncoder<'a> {
@@ -471,12 +485,13 @@ impl<'a> PrettyEncoder<'a> {
         PrettyEncoder {
             wr: wr,
             indent: 0,
+            error: Ok(())
         }
     }
 }
 
 impl<'a> serialize::Encoder for PrettyEncoder<'a> {
-    fn emit_nil(&mut self) { write!(self.wr, "null") }
+    fn emit_nil(&mut self) { if_ok!(write!(self.wr, "null")); }
 
     fn emit_uint(&mut self, v: uint) { self.emit_f64(v as f64); }
     fn emit_u64(&mut self, v: u64) { self.emit_f64(v as f64); }
@@ -492,19 +507,21 @@ impl<'a> serialize::Encoder for PrettyEncoder<'a> {
 
     fn emit_bool(&mut self, v: bool) {
         if v {
-            write!(self.wr, "true");
+            if_ok!(write!(self.wr, "true"));
         } else {
-            write!(self.wr, "false");
+            if_ok!(write!(self.wr, "false"));
         }
     }
 
     fn emit_f64(&mut self, v: f64) {
-        write!(self.wr, "{}", f64::to_str_digits(v, 6u))
+        if_ok!(write!(self.wr, "{}", f64::to_str_digits(v, 6u)));
     }
     fn emit_f32(&mut self, v: f32) { self.emit_f64(v as f64); }
 
     fn emit_char(&mut self, v: char) { self.emit_str(str::from_char(v)) }
-    fn emit_str(&mut self, v: &str) { write!(self.wr, "{}", escape_str(v)); }
+    fn emit_str(&mut self, v: &str) {
+        if_ok!(write!(self.wr, "{}", escape_str(v)));
+    }
 
     fn emit_enum(&mut self, _name: &str, f: |&mut PrettyEncoder<'a>|) {
         f(self)
@@ -516,13 +533,14 @@ impl<'a> serialize::Encoder for PrettyEncoder<'a> {
                          cnt: uint,
                          f: |&mut PrettyEncoder<'a>|) {
         if cnt == 0 {
-            write!(self.wr, "{}", escape_str(name));
+            if_ok!(write!(self.wr, "{}", escape_str(name)));
         } else {
             self.indent += 2;
-            write!(self.wr, "[\n{}{},\n", spaces(self.indent), escape_str(name));
+            if_ok!(write!(self.wr, "[\n{}{},\n", spaces(self.indent),
+                          escape_str(name)));
             f(self);
             self.indent -= 2;
-            write!(self.wr, "\n{}]", spaces(self.indent));
+            if_ok!(write!(self.wr, "\n{}]", spaces(self.indent)));
         }
     }
 
@@ -530,9 +548,9 @@ impl<'a> serialize::Encoder for PrettyEncoder<'a> {
                              idx: uint,
                              f: |&mut PrettyEncoder<'a>|) {
         if idx != 0 {
-            write!(self.wr, ",\n");
+            if_ok!(write!(self.wr, ",\n"));
         }
-        write!(self.wr, "{}", spaces(self.indent));
+        if_ok!(write!(self.wr, "{}", spaces(self.indent)));
         f(self)
     }
 
@@ -557,13 +575,13 @@ impl<'a> serialize::Encoder for PrettyEncoder<'a> {
                    len: uint,
                    f: |&mut PrettyEncoder<'a>|) {
         if len == 0 {
-            write!(self.wr, "\\{\\}");
+            if_ok!(write!(self.wr, "\\{\\}"));
         } else {
-            write!(self.wr, "\\{");
+            if_ok!(write!(self.wr, "\\{"));
             self.indent += 2;
             f(self);
             self.indent -= 2;
-            write!(self.wr, "\n{}\\}", spaces(self.indent));
+            if_ok!(write!(self.wr, "\n{}\\}", spaces(self.indent)));
         }
     }
 
@@ -572,11 +590,11 @@ impl<'a> serialize::Encoder for PrettyEncoder<'a> {
                          idx: uint,
                          f: |&mut PrettyEncoder<'a>|) {
         if idx == 0 {
-            write!(self.wr, "\n");
+            if_ok!(write!(self.wr, "\n"));
         } else {
-            write!(self.wr, ",\n");
+            if_ok!(write!(self.wr, ",\n"));
         }
-        write!(self.wr, "{}{}: ", spaces(self.indent), escape_str(name));
+        if_ok!(write!(self.wr, "{}{}: ", spaces(self.indent), escape_str(name)));
         f(self);
     }
 
@@ -605,50 +623,50 @@ impl<'a> serialize::Encoder for PrettyEncoder<'a> {
 
     fn emit_seq(&mut self, len: uint, f: |&mut PrettyEncoder<'a>|) {
         if len == 0 {
-            write!(self.wr, "[]");
+            if_ok!(write!(self.wr, "[]"));
         } else {
-            write!(self.wr, "[");
+            if_ok!(write!(self.wr, "["));
             self.indent += 2;
             f(self);
             self.indent -= 2;
-            write!(self.wr, "\n{}]", spaces(self.indent));
+            if_ok!(write!(self.wr, "\n{}]", spaces(self.indent)));
         }
     }
 
     fn emit_seq_elt(&mut self, idx: uint, f: |&mut PrettyEncoder<'a>|) {
         if idx == 0 {
-            write!(self.wr, "\n");
+            if_ok!(write!(self.wr, "\n"));
         } else {
-            write!(self.wr, ",\n");
+            if_ok!(write!(self.wr, ",\n"));
         }
-        write!(self.wr, "{}", spaces(self.indent));
+        if_ok!(write!(self.wr, "{}", spaces(self.indent)));
         f(self)
     }
 
     fn emit_map(&mut self, len: uint, f: |&mut PrettyEncoder<'a>|) {
         if len == 0 {
-            write!(self.wr, "\\{\\}");
+            if_ok!(write!(self.wr, "\\{\\}"));
         } else {
-            write!(self.wr, "\\{");
+            if_ok!(write!(self.wr, "\\{"));
             self.indent += 2;
             f(self);
             self.indent -= 2;
-            write!(self.wr, "\n{}\\}", spaces(self.indent));
+            if_ok!(write!(self.wr, "\n{}\\}", spaces(self.indent)));
         }
     }
 
     fn emit_map_elt_key(&mut self, idx: uint, f: |&mut PrettyEncoder<'a>|) {
         if idx == 0 {
-            write!(self.wr, "\n");
+            if_ok!(write!(self.wr, "\n"));
         } else {
-            write!(self.wr, ",\n");
+            if_ok!(write!(self.wr, ",\n"));
         }
-        write!(self.wr, "{}", spaces(self.indent));
+        if_ok!(write!(self.wr, "{}", spaces(self.indent)));
         f(self);
     }
 
     fn emit_map_elt_val(&mut self, _idx: uint, f: |&mut PrettyEncoder<'a>|) {
-        write!(self.wr, ": ");
+        if_ok!(write!(self.wr, ": "));
         f(self);
     }
 }
@@ -668,22 +686,24 @@ impl<E: serialize::Encoder> serialize::Encodable<E> for Json {
 
 impl Json{
     /// Encodes a json value into a io::writer.  Uses a single line.
-    pub fn to_writer(&self, wr: &mut io::Writer) {
+    pub fn to_writer(&self, wr: &mut io::Writer) -> io::IoResult<()> {
         let mut encoder = Encoder::new(wr);
-        self.encode(&mut encoder)
+        self.encode(&mut encoder);
+        encoder.error
     }
 
     /// Encodes a json value into a io::writer.
     /// Pretty-prints in a more readable format.
-    pub fn to_pretty_writer(&self, wr: &mut io::Writer) {
+    pub fn to_pretty_writer(&self, wr: &mut io::Writer) -> io::IoResult<()> {
         let mut encoder = PrettyEncoder::new(wr);
-        self.encode(&mut encoder)
+        self.encode(&mut encoder);
+        encoder.error
     }
 
     /// Encodes a json value into a string
     pub fn to_pretty_str(&self) -> ~str {
         let mut s = MemWriter::new();
-        self.to_pretty_writer(&mut s as &mut io::Writer);
+        self.to_pretty_writer(&mut s as &mut io::Writer).unwrap();
         str::from_utf8_owned(s.unwrap()).unwrap()
     }
 }
@@ -1067,7 +1087,14 @@ impl<T : Iterator<char>> Parser<T> {
 
 /// Decodes a json value from an `&mut io::Reader`
 pub fn from_reader(rdr: &mut io::Reader) -> Result<Json, Error> {
-    let s = str::from_utf8_owned(rdr.read_to_end()).unwrap();
+    let contents = match rdr.read_to_end() {
+        Ok(c) => c,
+        Err(e) => return Err(io_error_to_error(e))
+    };
+    let s = match str::from_utf8_owned(contents) {
+        Some(s) => s,
+        None => return Err(Error { line: 0, col: 0, msg: ~"contents not utf-8" })
+    };
     let mut parser = Parser::new(s.chars());
     parser.parse()
 }
@@ -1540,7 +1567,7 @@ impl to_str::ToStr for Json {
     /// Encodes a json value into a string
     fn to_str(&self) -> ~str {
         let mut s = MemWriter::new();
-        self.to_writer(&mut s as &mut io::Writer);
+        self.to_writer(&mut s as &mut io::Writer).unwrap();
         str::from_utf8_owned(s.unwrap()).unwrap()
     }
 }

src/libextra/lib.rs

@@ -34,6 +34,11 @@ Rust extras are part of the standard Rust distribution.
 #[deny(non_camel_case_types)];
 #[deny(missing_doc)];
 
+#[cfg(stage0)]
+macro_rules! if_ok (
+    ($e:expr) => (match $e { Ok(e) => e, Err(e) => return Err(e) })
+)
+
 // Utility modules
 
 pub mod c_vec;

src/libextra/stats.rs

@@ -322,14 +322,15 @@ pub fn winsorize(samples: &mut [f64], pct: f64) {
 }
 
 /// Render writes the min, max and quartiles of the provided `Summary` to the provided `Writer`.
-pub fn write_5_number_summary(w: &mut io::Writer, s: &Summary) {
+pub fn write_5_number_summary(w: &mut io::Writer,
+                              s: &Summary) -> io::IoResult<()> {
     let (q1,q2,q3) = s.quartiles;
     write!(w, "(min={}, q1={}, med={}, q3={}, max={})",
                      s.min,
                      q1,
                      q2,
                      q3,
-                     s.max);
+                     s.max)
 }
 
 /// Render a boxplot to the provided writer. The boxplot shows the min, max and quartiles of the
@@ -344,7 +345,8 @@ pub fn write_5_number_summary(w: &mut io::Writer, s: &Summary) {
 ///   10 |        [--****#******----------]          | 40
 /// ~~~~
 
-pub fn write_boxplot(w: &mut io::Writer, s: &Summary, width_hint: uint) {
+pub fn write_boxplot(w: &mut io::Writer, s: &Summary,
+                     width_hint: uint) -> io::IoResult<()> {
 
     let (q1,q2,q3) = s.quartiles;
 
@@ -374,48 +376,49 @@ pub fn write_boxplot(w: &mut io::Writer, s: &Summary, width_hint: uint) {
     let range_width = width_hint - overhead_width;;
     let char_step = range / (range_width as f64);
 
-    write!(w, "{} |", lostr);
+    if_ok!(write!(w, "{} |", lostr));
 
     let mut c = 0;
     let mut v = lo;
 
     while c < range_width && v < s.min {
-        write!(w, " ");
+        if_ok!(write!(w, " "));
         v += char_step;
         c += 1;
     }
-    write!(w, "[");
+    if_ok!(write!(w, "["));
     c += 1;
     while c < range_width && v < q1 {
-        write!(w, "-");
+        if_ok!(write!(w, "-"));
         v += char_step;
         c += 1;
     }
     while c < range_width && v < q2 {
-        write!(w, "*");
+        if_ok!(write!(w, "*"));
         v += char_step;
         c += 1;
     }
-    write!(w, r"\#");
+    if_ok!(write!(w, r"\#"));
     c += 1;
     while c < range_width && v < q3 {
-        write!(w, "*");
+        if_ok!(write!(w, "*"));
         v += char_step;
         c += 1;
     }
     while c < range_width && v < s.max {
-        write!(w, "-");
+        if_ok!(write!(w, "-"));
         v += char_step;
         c += 1;
     }
-    write!(w, "]");
+    if_ok!(write!(w, "]"));
     while c < range_width {
-        write!(w, " ");
+        if_ok!(write!(w, " "));
         v += char_step;
         c += 1;
     }
 
-    write!(w, "| {}", histr);
+    if_ok!(write!(w, "| {}", histr));
+    Ok(())
 }
 
 /// Returns a HashMap with the number of occurrences of every element in the
@@ -453,11 +456,11 @@ mod tests {
 
         let mut w = io::stdout();
         let w = &mut w as &mut io::Writer;
-        write!(w, "\n");
-        write_5_number_summary(w, &summ2);
-        write!(w, "\n");
-        write_boxplot(w, &summ2, 50);
-        write!(w, "\n");
+        (write!(w, "\n")).unwrap();
+        write_5_number_summary(w, &summ2).unwrap();
+        (write!(w, "\n")).unwrap();
+        write_boxplot(w, &summ2, 50).unwrap();
+        (write!(w, "\n")).unwrap();
 
         assert_eq!(summ.sum, summ2.sum);
         assert_eq!(summ.min, summ2.min);
@@ -1000,7 +1003,7 @@ mod tests {
         fn t(s: &Summary, expected: ~str) {
             use std::io::MemWriter;
             let mut m = MemWriter::new();
-            write_boxplot(&mut m as &mut io::Writer, s, 30);
+            write_boxplot(&mut m as &mut io::Writer, s, 30).unwrap();
             let out = str::from_utf8_owned(m.unwrap()).unwrap();
             assert_eq!(out, expected);
         }

src/libextra/sync.rs

@@ -959,7 +959,7 @@ mod tests {
     fn test_mutex_cond_no_waiter() {
         let m = Mutex::new();
         let m2 = m.clone();
-        task::try(proc() {
+        let _ = task::try(proc() {
             m.lock_cond(|_x| { })
         });
         m2.lock_cond(|cond| {

src/libextra/tempfile.rs

@@ -38,7 +38,7 @@ impl TempDir {
         let mut r = rand::rng();
         for _ in range(0u, 1000) {
             let p = tmpdir.join(r.gen_ascii_str(16) + suffix);
-            match io::result(|| fs::mkdir(&p, io::UserRWX)) {
+            match fs::mkdir(&p, io::UserRWX) {
                 Err(..) => {}
                 Ok(()) => return Some(TempDir { path: Some(p) })
             }
@@ -73,7 +73,8 @@ impl Drop for TempDir {
     fn drop(&mut self) {
         for path in self.path.iter() {
             if path.exists() {
-                fs::rmdir_recursive(path);
+                // FIXME: is failing the right thing to do?
+                fs::rmdir_recursive(path).unwrap();
             }
         }
     }

src/libextra/test.rs

@@ -163,7 +163,11 @@ pub fn test_main(args: &[~str], tests: ~[TestDescAndFn]) {
             Some(Err(msg)) => fail!("{}", msg),
             None => return
         };
-    if !run_tests_console(&opts, tests) { fail!("Some tests failed"); }
+    match run_tests_console(&opts, tests) {
+        Ok(true) => {}
+        Ok(false) => fail!("Some tests failed"),
+        Err(e) => fail!("io error when running tests: {}", e),
+    }
 }
 
 // A variant optimized for invocation with a static test vector.
@@ -359,16 +363,17 @@ struct ConsoleTestState<T> {
 }
 
 impl<T: Writer> ConsoleTestState<T> {
-    pub fn new(opts: &TestOpts, _: Option<T>) -> ConsoleTestState<StdWriter> {
+    pub fn new(opts: &TestOpts,
+               _: Option<T>) -> io::IoResult<ConsoleTestState<StdWriter>> {
         let log_out = match opts.logfile {
-            Some(ref path) => File::create(path),
+            Some(ref path) => Some(if_ok!(File::create(path))),
             None => None
         };
         let out = match term::Terminal::new(io::stdout()) {
             Err(_) => Raw(io::stdout()),
             Ok(t) => Pretty(t)
         };
-        ConsoleTestState {
+        Ok(ConsoleTestState {
             out: out,
             log_out: log_out,
             use_color: use_color(),
@@ -380,100 +385,103 @@ impl<T: Writer> ConsoleTestState<T> {
             metrics: MetricMap::new(),
             failures: ~[],
             max_name_len: 0u,
-        }
+        })
     }
 
-    pub fn write_ok(&mut self) {
-        self.write_pretty("ok", term::color::GREEN);
+    pub fn write_ok(&mut self) -> io::IoResult<()> {
+        self.write_pretty("ok", term::color::GREEN)
     }
 
-    pub fn write_failed(&mut self) {
-        self.write_pretty("FAILED", term::color::RED);
+    pub fn write_failed(&mut self) -> io::IoResult<()> {
+        self.write_pretty("FAILED", term::color::RED)
     }
 
-    pub fn write_ignored(&mut self) {
-        self.write_pretty("ignored", term::color::YELLOW);
+    pub fn write_ignored(&mut self) -> io::IoResult<()> {
+        self.write_pretty("ignored", term::color::YELLOW)
     }
 
-    pub fn write_metric(&mut self) {
-        self.write_pretty("metric", term::color::CYAN);
+    pub fn write_metric(&mut self) -> io::IoResult<()> {
+        self.write_pretty("metric", term::color::CYAN)
     }
 
-    pub fn write_bench(&mut self) {
-        self.write_pretty("bench", term::color::CYAN);
+    pub fn write_bench(&mut self) -> io::IoResult<()> {
+        self.write_pretty("bench", term::color::CYAN)
     }
 
-    pub fn write_added(&mut self) {
-        self.write_pretty("added", term::color::GREEN);
+    pub fn write_added(&mut self) -> io::IoResult<()> {
+        self.write_pretty("added", term::color::GREEN)
     }
 
-    pub fn write_improved(&mut self) {
-        self.write_pretty("improved", term::color::GREEN);
+    pub fn write_improved(&mut self) -> io::IoResult<()> {
+        self.write_pretty("improved", term::color::GREEN)
     }
 
-    pub fn write_removed(&mut self) {
-        self.write_pretty("removed", term::color::YELLOW);
+    pub fn write_removed(&mut self) -> io::IoResult<()> {
+        self.write_pretty("removed", term::color::YELLOW)
     }
 
-    pub fn write_regressed(&mut self) {
-        self.write_pretty("regressed", term::color::RED);
+    pub fn write_regressed(&mut self) -> io::IoResult<()> {
+        self.write_pretty("regressed", term::color::RED)
     }
 
     pub fn write_pretty(&mut self,
                         word: &str,
-                        color: term::color::Color) {
+                        color: term::color::Color) -> io::IoResult<()> {
         match self.out {
             Pretty(ref mut term) => {
                 if self.use_color {
-                    term.fg(color);
+                    if_ok!(term.fg(color));
                 }
-                term.write(word.as_bytes());
+                if_ok!(term.write(word.as_bytes()));
                 if self.use_color {
-                    term.reset();
+                    if_ok!(term.reset());
                 }
+                Ok(())
             }
             Raw(ref mut stdout) => stdout.write(word.as_bytes())
         }
     }
 
-    pub fn write_plain(&mut self, s: &str) {
+    pub fn write_plain(&mut self, s: &str) -> io::IoResult<()> {
         match self.out {
             Pretty(ref mut term) => term.write(s.as_bytes()),
             Raw(ref mut stdout) => stdout.write(s.as_bytes())
         }
     }
 
-    pub fn write_run_start(&mut self, len: uint) {
+    pub fn write_run_start(&mut self, len: uint) -> io::IoResult<()> {
         self.total = len;
         let noun = if len != 1 { &"tests" } else { &"test" };
-        self.write_plain(format!("\nrunning {} {}\n", len, noun));
+        self.write_plain(format!("\nrunning {} {}\n", len, noun))
     }
 
-    pub fn write_test_start(&mut self, test: &TestDesc, align: NamePadding) {
+    pub fn write_test_start(&mut self, test: &TestDesc,
+                            align: NamePadding) -> io::IoResult<()> {
         let name = test.padded_name(self.max_name_len, align);
-        self.write_plain(format!("test {} ... ", name));
+        self.write_plain(format!("test {} ... ", name))
     }
 
-    pub fn write_result(&mut self, result: &TestResult) {
-        match *result {
+    pub fn write_result(&mut self, result: &TestResult) -> io::IoResult<()> {
+        if_ok!(match *result {
             TrOk => self.write_ok(),
             TrFailed => self.write_failed(),
             TrIgnored => self.write_ignored(),
             TrMetrics(ref mm) => {
-                self.write_metric();
-                self.write_plain(format!(": {}", fmt_metrics(mm)));
+                if_ok!(self.write_metric());
+                self.write_plain(format!(": {}", fmt_metrics(mm)))
             }
             TrBench(ref bs) => {
-                self.write_bench();
-                self.write_plain(format!(": {}", fmt_bench_samples(bs)));
+                if_ok!(self.write_bench());
+                self.write_plain(format!(": {}", fmt_bench_samples(bs)))
             }
-        }
-        self.write_plain("\n");
+        });
+        self.write_plain("\n")
     }
 
-    pub fn write_log(&mut self, test: &TestDesc, result: &TestResult) {
+    pub fn write_log(&mut self, test: &TestDesc,
+                     result: &TestResult) -> io::IoResult<()> {
         match self.log_out {
-            None => (),
+            None => Ok(()),
             Some(ref mut o) => {
                 let s = format!("{} {}\n", match *result {
                         TrOk => ~"ok",
@@ -482,24 +490,25 @@ impl<T: Writer> ConsoleTestState<T> {
                         TrMetrics(ref mm) => fmt_metrics(mm),
                         TrBench(ref bs) => fmt_bench_samples(bs)
                     }, test.name.to_str());
-                o.write(s.as_bytes());
+                o.write(s.as_bytes())
             }
         }
     }
 
-    pub fn write_failures(&mut self) {
-        self.write_plain("\nfailures:\n");
+    pub fn write_failures(&mut self) -> io::IoResult<()> {
+        if_ok!(self.write_plain("\nfailures:\n"));
         let mut failures = ~[];
         for f in self.failures.iter() {
             failures.push(f.name.to_str());
         }
         failures.sort();
         for name in failures.iter() {
-            self.write_plain(format!("    {}\n", name.to_str()));
+            if_ok!(self.write_plain(format!("    {}\n", name.to_str())));
         }
+        Ok(())
     }
 
-    pub fn write_metric_diff(&mut self, diff: &MetricDiff) {
+    pub fn write_metric_diff(&mut self, diff: &MetricDiff) -> io::IoResult<()> {
         let mut noise = 0;
         let mut improved = 0;
         let mut regressed = 0;
@@ -511,77 +520,82 @@ impl<T: Writer> ConsoleTestState<T> {
                 LikelyNoise => noise += 1,
                 MetricAdded => {
                     added += 1;
-                    self.write_added();
-                    self.write_plain(format!(": {}\n", *k));
+                    if_ok!(self.write_added());
+                    if_ok!(self.write_plain(format!(": {}\n", *k)));
                 }
                 MetricRemoved => {
                     removed += 1;
-                    self.write_removed();
-                    self.write_plain(format!(": {}\n", *k));
+                    if_ok!(self.write_removed());
+                    if_ok!(self.write_plain(format!(": {}\n", *k)));
                 }
                 Improvement(pct) => {
                     improved += 1;
-                    self.write_plain(format!(": {}", *k));
-                    self.write_improved();
-                    self.write_plain(format!(" by {:.2f}%\n", pct as f64));
+                    if_ok!(self.write_plain(format!(": {}", *k)));
+                    if_ok!(self.write_improved());
+                    if_ok!(self.write_plain(format!(" by {:.2f}%\n", pct as f64)));
                 }
                 Regression(pct) => {
                     regressed += 1;
-                    self.write_plain(format!(": {}", *k));
-                    self.write_regressed();
-                    self.write_plain(format!(" by {:.2f}%\n", pct as f64));
+                    if_ok!(self.write_plain(format!(": {}", *k)));
+                    if_ok!(self.write_regressed());
+                    if_ok!(self.write_plain(format!(" by {:.2f}%\n", pct as f64)));
                 }
             }
         }
-        self.write_plain(format!("result of ratchet: {} matrics added, {} removed, \
-                                  {} improved, {} regressed, {} noise\n",
-                                 added, removed, improved, regressed, noise));
+        if_ok!(self.write_plain(format!("result of ratchet: {} matrics added, \
+                                        {} removed, {} improved, {} regressed, \
+                                        {} noise\n",
+                                       added, removed, improved, regressed,
+                                       noise)));
         if regressed == 0 {
-            self.write_plain("updated ratchet file\n");
+            if_ok!(self.write_plain("updated ratchet file\n"));
         } else {
-            self.write_plain("left ratchet file untouched\n");
+            if_ok!(self.write_plain("left ratchet file untouched\n"));
         }
+        Ok(())
     }
 
     pub fn write_run_finish(&mut self,
                             ratchet_metrics: &Option<Path>,
-                            ratchet_pct: Option<f64>) -> bool {
+                            ratchet_pct: Option<f64>) -> io::IoResult<bool> {
         assert!(self.passed + self.failed + self.ignored + self.measured == self.total);
 
         let ratchet_success = match *ratchet_metrics {
             None => true,
             Some(ref pth) => {
-                self.write_plain(format!("\nusing metrics ratcher: {}\n", pth.display()));
+                if_ok!(self.write_plain(format!("\nusing metrics ratcher: {}\n",
+                                        pth.display())));
                 match ratchet_pct {
                     None => (),
                     Some(pct) =>
-                        self.write_plain(format!("with noise-tolerance forced to: {}%\n",
-                                                 pct))
+                        if_ok!(self.write_plain(format!("with noise-tolerance \
+                                                         forced to: {}%\n",
+                                                        pct)))
                 }
                 let (diff, ok) = self.metrics.ratchet(pth, ratchet_pct);
-                self.write_metric_diff(&diff);
+                if_ok!(self.write_metric_diff(&diff));
                 ok
             }
         };
 
         let test_success = self.failed == 0u;
         if !test_success {
-            self.write_failures();
+            if_ok!(self.write_failures());
         }
 
         let success = ratchet_success && test_success;
 
-        self.write_plain("\ntest result: ");
+        if_ok!(self.write_plain("\ntest result: "));
         if success {
             // There's no parallelism at this point so it's safe to use color
-            self.write_ok();
+            if_ok!(self.write_ok());
         } else {
-            self.write_failed();
+            if_ok!(self.write_failed());
         }
         let s = format!(". {} passed; {} failed; {} ignored; {} measured\n\n",
                         self.passed, self.failed, self.ignored, self.measured);
-        self.write_plain(s);
-        return success;
+        if_ok!(self.write_plain(s));
+        return Ok(success);
     }
 }
 
@@ -611,15 +625,16 @@ pub fn fmt_bench_samples(bs: &BenchSamples) -> ~str {
 
 // A simple console test runner
 pub fn run_tests_console(opts: &TestOpts,
-                         tests: ~[TestDescAndFn]) -> bool {
-    fn callback<T: Writer>(event: &TestEvent, st: &mut ConsoleTestState<T>) {
+                         tests: ~[TestDescAndFn]) -> io::IoResult<bool> {
+    fn callback<T: Writer>(event: &TestEvent,
+                           st: &mut ConsoleTestState<T>) -> io::IoResult<()> {
         debug!("callback(event={:?})", event);
         match (*event).clone() {
             TeFiltered(ref filtered_tests) => st.write_run_start(filtered_tests.len()),
             TeWait(ref test, padding) => st.write_test_start(test, padding),
             TeResult(test, result) => {
-                st.write_log(&test, &result);
-                st.write_result(&result);
+                if_ok!(st.write_log(&test, &result));
+                if_ok!(st.write_result(&result));
                 match result {
                     TrOk => st.passed += 1,
                     TrIgnored => st.ignored += 1,
@@ -643,10 +658,11 @@ pub fn run_tests_console(opts: &TestOpts,
                         st.failures.push(test);
                     }
                 }
+                Ok(())
             }
         }
     }
-    let mut st = ConsoleTestState::new(opts, None::<StdWriter>);
+    let mut st = if_ok!(ConsoleTestState::new(opts, None::<StdWriter>));
     fn len_if_padded(t: &TestDescAndFn) -> uint {
         match t.testfn.padding() {
             PadNone => 0u,
@@ -661,12 +677,13 @@ pub fn run_tests_console(opts: &TestOpts,
         },
         None => {}
     }
-    run_tests(opts, tests, |x| callback(&x, &mut st));
+    if_ok!(run_tests(opts, tests, |x| callback(&x, &mut st)));
     match opts.save_metrics {
         None => (),
         Some(ref pth) => {
-            st.metrics.save(pth);
-            st.write_plain(format!("\nmetrics saved to: {}", pth.display()));
+            if_ok!(st.metrics.save(pth));
+            if_ok!(st.write_plain(format!("\nmetrics saved to: {}",
+                                          pth.display())));
         }
     }
     return st.write_run_finish(&opts.ratchet_metrics, opts.ratchet_noise_percent);
@@ -703,7 +720,7 @@ fn should_sort_failures_before_printing_them() {
         failures: ~[test_b, test_a]
     };
 
-    st.write_failures();
+    st.write_failures().unwrap();
     let s = match st.out {
         Raw(ref m) => str::from_utf8(m.get_ref()).unwrap(),
         Pretty(_) => unreachable!()
@@ -728,11 +745,11 @@ pub type MonitorMsg = (TestDesc, TestResult);
 
 fn run_tests(opts: &TestOpts,
              tests: ~[TestDescAndFn],
-             callback: |e: TestEvent|) {
+             callback: |e: TestEvent| -> io::IoResult<()>) -> io::IoResult<()> {
     let filtered_tests = filter_tests(opts, tests);
     let filtered_descs = filtered_tests.map(|t| t.desc.clone());
 
-    callback(TeFiltered(filtered_descs));
+    if_ok!(callback(TeFiltered(filtered_descs)));
 
     let (filtered_tests, filtered_benchs_and_metrics) =
         filtered_tests.partition(|e| {
@@ -760,7 +777,7 @@ fn run_tests(opts: &TestOpts,
                 // We are doing one test at a time so we can print the name
                 // of the test before we run it. Useful for debugging tests
                 // that hang forever.
-                callback(TeWait(test.desc.clone(), test.testfn.padding()));
+                if_ok!(callback(TeWait(test.desc.clone(), test.testfn.padding())));
             }
             run_test(!opts.run_tests, test, ch.clone());
             pending += 1;
@@ -768,20 +785,21 @@ fn run_tests(opts: &TestOpts,
 
         let (desc, result) = p.recv();
         if concurrency != 1 {
-            callback(TeWait(desc.clone(), PadNone));
+            if_ok!(callback(TeWait(desc.clone(), PadNone)));
         }
-        callback(TeResult(desc, result));
+        if_ok!(callback(TeResult(desc, result)));
         pending -= 1;
     }
 
     // All benchmarks run at the end, in serial.
     // (this includes metric fns)
     for b in filtered_benchs_and_metrics.move_iter() {
-        callback(TeWait(b.desc.clone(), b.testfn.padding()));
+        if_ok!(callback(TeWait(b.desc.clone(), b.testfn.padding())));
         run_test(!opts.run_benchmarks, b, ch.clone());
         let (test, result) = p.recv();
-        callback(TeResult(test, result));
+        if_ok!(callback(TeResult(test, result)));
     }
+    Ok(())
 }
 
 fn get_concurrency() -> uint {
@@ -943,17 +961,22 @@ impl MetricMap {
     }
 
     /// Load MetricDiff from a file.
+    ///
+    /// # Failure
+    ///
+    /// This function will fail if the path does not exist or the path does not
+    /// contain a valid metric map.
     pub fn load(p: &Path) -> MetricMap {
         assert!(p.exists());
-        let mut f = File::open(p);
+        let mut f = File::open(p).unwrap();
         let value = json::from_reader(&mut f as &mut io::Reader).unwrap();
         let mut decoder = json::Decoder::new(value);
         MetricMap(Decodable::decode(&mut decoder))
     }
 
     /// Write MetricDiff to a file.
-    pub fn save(&self, p: &Path) {
-        let mut file = File::create(p);
+    pub fn save(&self, p: &Path) -> io::IoResult<()> {
+        let mut file = if_ok!(File::create(p));
         let MetricMap(ref map) = *self;
         map.to_json().to_pretty_writer(&mut file)
     }
@@ -1060,7 +1083,7 @@ impl MetricMap {
 
         if ok {
             debug!("rewriting file '{:?}' with updated metrics", p);
-            self.save(p);
+            self.save(p).unwrap();
         }
         return (diff, ok)
     }
@@ -1462,7 +1485,7 @@ mod tests {
         m2.insert_metric("runtime", 1100.0, 2.0);
         m2.insert_metric("throughput", 50.0, 2.0);
 
-        m1.save(&pth);
+        m1.save(&pth).unwrap();
 
         // Ask for a ratchet that should fail to advance.
         let (diff1, ok1) = m2.ratchet(&pth, None);

src/libextra/time.rs

@@ -766,14 +766,14 @@ pub fn strptime(s: &str, format: &str) -> Result<Tm, ~str> {
 
         let mut buf = [0];
         let c = match rdr.read(buf) {
-            Some(..) => buf[0] as char,
-            None => break
+            Ok(..) => buf[0] as char,
+            Err(..) => break
         };
         match c {
             '%' => {
                 let ch = match rdr.read(buf) {
-                    Some(..) => buf[0] as char,
-                    None => break
+                    Ok(..) => buf[0] as char,
+                    Err(..) => break
                 };
                 match parse_type(s, pos, ch, &mut tm) {
                     Ok(next) => pos = next,
@@ -787,7 +787,7 @@ pub fn strptime(s: &str, format: &str) -> Result<Tm, ~str> {
         }
     }
 
-    if pos == len && rdr.tell() as uint == format.len() {
+    if pos == len && rdr.tell().unwrap() == format.len() as u64 {
         Ok(Tm {
             tm_sec: tm.tm_sec,
             tm_min: tm.tm_min,
@@ -1017,12 +1017,12 @@ pub fn strftime(format: &str, tm: &Tm) -> ~str {
     loop {
         let mut b = [0];
         let ch = match rdr.read(b) {
-            Some(..) => b[0],
-            None => break,
+            Ok(..) => b[0],
+            Err(..) => break,
         };
         match ch as char {
             '%' => {
-                rdr.read(b);
+                rdr.read(b).unwrap();
                 let s = parse_type(b[0] as char, tm);
                 buf.push_all(s.as_bytes());
             }

src/libextra/url.rs

@@ -102,8 +102,8 @@ fn encode_inner(s: &str, full_url: bool) -> ~str {
     loop {
         let mut buf = [0];
         let ch = match rdr.read(buf) {
-            None => break,
-            Some(..) => buf[0] as char,
+            Err(..) => break,
+            Ok(..) => buf[0] as char,
         };
 
         match ch {
@@ -166,14 +166,14 @@ fn decode_inner(s: &str, full_url: bool) -> ~str {
     loop {
         let mut buf = [0];
         let ch = match rdr.read(buf) {
-            None => break,
-            Some(..) => buf[0] as char
+            Err(..) => break,
+            Ok(..) => buf[0] as char
         };
         match ch {
           '%' => {
             let mut bytes = [0, 0];
             match rdr.read(bytes) {
-                Some(2) => {}
+                Ok(2) => {}
                 _ => fail!() // FIXME: malformed url?
             }
             let ch = uint::parse_bytes(bytes, 16u).unwrap() as u8 as char;
@@ -228,8 +228,8 @@ fn encode_plus(s: &str) -> ~str {
     loop {
         let mut buf = [0];
         let ch = match rdr.read(buf) {
-            Some(..) => buf[0] as char,
-            None => break,
+            Ok(..) => buf[0] as char,
+            Err(..) => break,
         };
         match ch {
           'A' .. 'Z' | 'a' .. 'z' | '0' .. '9' | '_' | '.' | '-' => {
@@ -282,8 +282,8 @@ pub fn decode_form_urlencoded(s: &[u8]) -> HashMap<~str, ~[~str]> {
     loop {
         let mut buf = [0];
         let ch = match rdr.read(buf) {
-            Some(..) => buf[0] as char,
-            None => break,
+            Ok(..) => buf[0] as char,
+            Err(..) => break,
         };
         match ch {
             '&' | ';' => {
@@ -307,7 +307,7 @@ pub fn decode_form_urlencoded(s: &[u8]) -> HashMap<~str, ~[~str]> {
                     '%' => {
                         let mut bytes = [0, 0];
                         match rdr.read(bytes) {
-                            Some(2) => {}
+                            Ok(2) => {}
                             _ => fail!() // FIXME: malformed?
                         }
                         uint::parse_bytes(bytes, 16u).unwrap() as u8 as char
@@ -347,12 +347,12 @@ fn split_char_first(s: &str, c: char) -> (~str, ~str) {
     loop {
         let mut buf = [0];
         let ch = match rdr.read(buf) {
-            Some(..) => buf[0] as char,
-            None => break,
+            Ok(..) => buf[0] as char,
+            Err(..) => break,
         };
         if ch == c {
             // found a match, adjust markers
-            index = (rdr.tell() as uint) - 1;
+            index = (rdr.tell().unwrap() as uint) - 1;
             mat = 1;
             break;
         }

src/libextra/uuid.rs

@@ -821,7 +821,7 @@ mod bench {
     pub fn parse_str(bh: &mut BenchHarness) {
         let s = "urn:uuid:F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4";
         bh.iter(|| {
-            Uuid::parse_string(s);
+            Uuid::parse_string(s).unwrap();
         })
     }
 }

src/libextra/workcache.rs

@@ -172,20 +172,19 @@ impl Database {
     }
 
     // FIXME #4330: This should have &mut self and should set self.db_dirty to false.
-    fn save(&self) {
+    fn save(&self) -> io::IoResult<()> {
         let mut f = File::create(&self.db_filename);
-        self.db_cache.to_json().to_pretty_writer(&mut f);
+        self.db_cache.to_json().to_pretty_writer(&mut f)
     }
 
     fn load(&mut self) {
         assert!(!self.db_dirty);
         assert!(self.db_filename.exists());
-        match io::result(|| File::open(&self.db_filename)) {
+        match File::open(&self.db_filename) {
             Err(e) => fail!("Couldn't load workcache database {}: {}",
                             self.db_filename.display(),
-                            e.desc),
-            Ok(r) => {
-                let mut stream = r.unwrap();
+                            e),
+            Ok(mut stream) => {
                 match json::from_reader(&mut stream) {
                     Err(e) => fail!("Couldn't parse workcache database (from file {}): {}",
                                     self.db_filename.display(), e.to_str()),
@@ -203,7 +202,8 @@ impl Database {
 impl Drop for Database {
     fn drop(&mut self) {
         if self.db_dirty {
-            self.save();
+            // FIXME: is failing the right thing to do here
+            self.save().unwrap();
         }
     }
 }
@@ -473,13 +473,13 @@ fn test() {
     fn make_path(filename: ~str) -> Path {
         let pth = os::self_exe_path().expect("workcache::test failed").with_filename(filename);
         if pth.exists() {
-            fs::unlink(&pth);
+            fs::unlink(&pth).unwrap();
         }
         return pth;
     }
 
     let pth = make_path(~"foo.c");
-    File::create(&pth).write(bytes!("int main() { return 0; }"));
+    File::create(&pth).write(bytes!("int main() { return 0; }")).unwrap();
 
     let db_path = make_path(~"db.json");
 
@@ -491,7 +491,8 @@ fn test() {
         let subcx = cx.clone();
         let pth = pth.clone();
 
-        let file_content = from_utf8_owned(File::open(&pth).read_to_end()).unwrap();
+        let contents = File::open(&pth).read_to_end().unwrap();
+        let file_content = from_utf8_owned(contents).unwrap();
 
         // FIXME (#9639): This needs to handle non-utf8 paths
         prep.declare_input("file", pth.as_str().unwrap(), file_content);
@@ -500,7 +501,7 @@ fn test() {
             // FIXME (#9639): This needs to handle non-utf8 paths
             run::process_status("gcc", [pth.as_str().unwrap().to_owned(),
                                         ~"-o",
-                                        out.as_str().unwrap().to_owned()]);
+                                        out.as_str().unwrap().to_owned()]).unwrap();
 
             let _proof_of_concept = subcx.prep("subfn");
             // Could run sub-rules inside here.

src/libglob/lib.rs

@@ -29,7 +29,6 @@
 #[license = "MIT/ASL2"];
 
 use std::{os, path};
-use std::io;
 use std::io::fs;
 use std::path::is_sep;
 
@@ -153,7 +152,7 @@ impl Iterator<Path> for Paths {
 }
 
 fn list_dir_sorted(path: &Path) -> ~[Path] {
-    match io::result(|| fs::readdir(path)) {
+    match fs::readdir(path) {
         Ok(mut children) => {
             children.sort_by(|p1, p2| p2.filename().cmp(&p1.filename()));
             children

src/libgreen/macros.rs

@@ -56,16 +56,17 @@ pub fn dumb_println(args: &fmt::Arguments) {
 
     struct Stderr;
     impl io::Writer for Stderr {
-        fn write(&mut self, data: &[u8]) {
+        fn write(&mut self, data: &[u8]) -> io::IoResult<()> {
             unsafe {
                 libc::write(libc::STDERR_FILENO,
                             data.as_ptr() as *libc::c_void,
                             data.len() as libc::size_t);
             }
+            Ok(()) // just ignore the result
         }
     }
     let mut w = Stderr;
-    fmt::writeln(&mut w as &mut io::Writer, args);
+    let _ = fmt::writeln(&mut w as &mut io::Writer, args);
 }
 
 pub fn abort(msg: &str) -> ! {

src/libnative/bookkeeping.rs

@@ -23,7 +23,7 @@ static mut TASK_COUNT: atomics::AtomicUint = atomics::INIT_ATOMIC_UINT;
 static mut TASK_LOCK: Mutex = MUTEX_INIT;
 
 pub fn increment() {
-    unsafe { TASK_COUNT.fetch_add(1, atomics::SeqCst); }
+    let _ = unsafe { TASK_COUNT.fetch_add(1, atomics::SeqCst) };
 }
 
 pub fn decrement() {

src/libnative/io/file.rs

@@ -111,17 +111,14 @@ impl FileDesc {
 }
 
 impl io::Reader for FileDesc {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        match self.inner_read(buf) { Ok(n) => Some(n), Err(..) => None }
+    fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
+        self.inner_read(buf)
     }
 }
 
 impl io::Writer for FileDesc {
-    fn write(&mut self, buf: &[u8]) {
-        match self.inner_write(buf) {
-            Ok(()) => {}
-            Err(e) => { io::io_error::cond.raise(e); }
-        }
+    fn write(&mut self, buf: &[u8]) -> io::IoResult<()> {
+        self.inner_write(buf)
     }
 }
 
@@ -425,7 +422,7 @@ impl rtio::RtioFileStream for CFile {
 
 impl Drop for CFile {
     fn drop(&mut self) {
-        unsafe { libc::fclose(self.file); }
+        unsafe { let _ = libc::fclose(self.file); }
     }
 }
 
@@ -515,7 +512,7 @@ pub fn readdir(p: &CString) -> IoResult<~[Path]> {
                     paths.push(Path::new(cstr));
                     entry_ptr = readdir(dir_ptr);
                 }
-                closedir(dir_ptr);
+                assert_eq!(closedir(dir_ptr), 0);
                 Ok(paths)
             } else {
                 Err(super::last_error())
@@ -564,7 +561,7 @@ pub fn readdir(p: &CString) -> IoResult<~[Path]> {
                         }
                         more_files = FindNextFileW(find_handle, wfd_ptr as HANDLE);
                     }
-                    FindClose(find_handle);
+                    assert!(FindClose(find_handle) != 0);
                     free(wfd_ptr as *mut c_void);
                     Ok(paths)
                 } else {
@@ -686,7 +683,9 @@ pub fn readlink(p: &CString) -> IoResult<Path> {
                                   ptr::mut_null())
             })
         };
-        if handle == ptr::mut_null() { return Err(super::last_error()) }
+        if handle as int == libc::INVALID_HANDLE_VALUE as int {
+            return Err(super::last_error())
+        }
         let ret = fill_utf16_buf_and_decode(|buf, sz| {
             unsafe {
                 libc::GetFinalPathNameByHandleW(handle, buf as *u16, sz,
@@ -697,7 +696,7 @@ pub fn readlink(p: &CString) -> IoResult<Path> {
             Some(s) => Ok(Path::new(s)),
             None => Err(super::last_error()),
         };
-        unsafe { libc::CloseHandle(handle) };
+        assert!(unsafe { libc::CloseHandle(handle) } != 0);
         return ret;
 
     }
@@ -935,7 +934,7 @@ mod tests {
             let mut reader = FileDesc::new(input, true);
             let mut writer = FileDesc::new(out, true);
 
-            writer.inner_write(bytes!("test"));
+            writer.inner_write(bytes!("test")).unwrap();
             let mut buf = [0u8, ..4];
             match reader.inner_read(buf) {
                 Ok(4) => {
@@ -960,9 +959,9 @@ mod tests {
             assert!(!f.is_null());
             let mut file = CFile::new(f);
 
-            file.write(bytes!("test"));
+            file.write(bytes!("test")).unwrap();
             let mut buf = [0u8, ..4];
-            file.seek(0, io::SeekSet);
+            let _ = file.seek(0, io::SeekSet).unwrap();
             match file.read(buf) {
                 Ok(4) => {
                     assert_eq!(buf[0], 't' as u8);

src/libnative/io/net.rs

@@ -112,8 +112,8 @@ fn setsockopt<T>(fd: sock_t, opt: libc::c_int, val: libc::c_int,
     }
 }
 
-#[cfg(windows)] unsafe fn close(sock: sock_t) { libc::closesocket(sock); }
-#[cfg(unix)]    unsafe fn close(sock: sock_t) { libc::close(sock); }
+#[cfg(windows)] unsafe fn close(sock: sock_t) { let _ = libc::closesocket(sock); }
+#[cfg(unix)]    unsafe fn close(sock: sock_t) { let _ = libc::close(sock); }
 
 fn sockname(fd: sock_t,
             f: extern "system" unsafe fn(sock_t, *mut libc::sockaddr,

src/libnative/io/process.rs

@@ -102,9 +102,9 @@ impl Process {
                                    cwd.as_ref(), in_fd, out_fd, err_fd);
 
         unsafe {
-            for pipe in in_pipe.iter() { libc::close(pipe.input); }
-            for pipe in out_pipe.iter() { libc::close(pipe.out); }
-            for pipe in err_pipe.iter() { libc::close(pipe.out); }
+            for pipe in in_pipe.iter() { let _ = libc::close(pipe.input); }
+            for pipe in out_pipe.iter() { let _ = libc::close(pipe.out); }
+            for pipe in err_pipe.iter() { let _ = libc::close(pipe.out); }
         }
 
         match res {
@@ -149,9 +149,8 @@ impl rtio::RtioProcess for Process {
         unsafe fn killpid(pid: pid_t, signal: int) -> Result<(), io::IoError> {
             match signal {
                 io::process::PleaseExitSignal | io::process::MustDieSignal => {
-                    libc::funcs::extra::kernel32::TerminateProcess(
-                        cast::transmute(pid), 1);
-                    Ok(())
+                    let ret = libc::TerminateProcess(pid as libc::HANDLE, 1);
+                    super::mkerr_winbool(ret)
                 }
                 _ => Err(io::IoError {
                     kind: io::OtherIoError,
@@ -163,8 +162,8 @@ impl rtio::RtioProcess for Process {
 
         #[cfg(not(windows))]
         unsafe fn killpid(pid: pid_t, signal: int) -> Result<(), io::IoError> {
-            libc::funcs::posix88::signal::kill(pid, signal as c_int);
-            Ok(())
+            let r = libc::funcs::posix88::signal::kill(pid, signal as c_int);
+            super::mkerr_libc(r)
         }
     }
 }
@@ -255,9 +254,9 @@ fn spawn_process_os(prog: &str, args: &[~str],
             })
         });
 
-        CloseHandle(si.hStdInput);
-        CloseHandle(si.hStdOutput);
-        CloseHandle(si.hStdError);
+        assert!(CloseHandle(si.hStdInput) != 0);
+        assert!(CloseHandle(si.hStdOutput) != 0);
+        assert!(CloseHandle(si.hStdError) != 0);
 
         match create_err {
             Some(err) => return Err(err),
@@ -269,7 +268,7 @@ fn spawn_process_os(prog: &str, args: &[~str],
         // able to close it later. We don't close the process handle however
         // because std::we want the process id to stay valid at least until the
         // calling code closes the process handle.
-        CloseHandle(pi.hThread);
+        assert!(CloseHandle(pi.hThread) != 0);
 
         Ok(SpawnProcessResult {
             pid: pi.dwProcessId as pid_t,
@@ -445,24 +444,24 @@ fn spawn_process_os(prog: &str, args: &[~str],
         rustrt::rust_unset_sigprocmask();
 
         if in_fd == -1 {
-            libc::close(libc::STDIN_FILENO);
+            let _ = libc::close(libc::STDIN_FILENO);
         } else if retry(|| dup2(in_fd, 0)) == -1 {
             fail!("failure in dup2(in_fd, 0): {}", os::last_os_error());
         }
         if out_fd == -1 {
-            libc::close(libc::STDOUT_FILENO);
+            let _ = libc::close(libc::STDOUT_FILENO);
         } else if retry(|| dup2(out_fd, 1)) == -1 {
             fail!("failure in dup2(out_fd, 1): {}", os::last_os_error());
         }
         if err_fd == -1 {
-            libc::close(libc::STDERR_FILENO);
+            let _ = libc::close(libc::STDERR_FILENO);
         } else if retry(|| dup2(err_fd, 2)) == -1 {
             fail!("failure in dup3(err_fd, 2): {}", os::last_os_error());
         }
         // close all other fds
         for fd in range(3, getdtablesize()).rev() {
             if fd != output.fd() {
-                close(fd as c_int);
+                let _ = close(fd as c_int);
             }
         }
 
@@ -478,7 +477,7 @@ fn spawn_process_os(prog: &str, args: &[~str],
             }
         });
         with_argv(prog, args, |argv| {
-            execvp(*argv, argv);
+            let _ = execvp(*argv, argv);
             let errno = os::errno();
             let bytes = [
                 (errno << 24) as u8,
@@ -576,9 +575,9 @@ fn with_dirp<T>(d: Option<&Path>, cb: |*libc::c_char| -> T) -> T {
 
 #[cfg(windows)]
 fn free_handle(handle: *()) {
-    unsafe {
-        libc::funcs::extra::kernel32::CloseHandle(cast::transmute(handle));
-    }
+    assert!(unsafe {
+        libc::CloseHandle(cast::transmute(handle)) != 0
+    })
 }
 
 #[cfg(unix)]
@@ -629,15 +628,15 @@ fn waitpid(pid: pid_t) -> p::ProcessExit {
             loop {
                 let mut status = 0;
                 if GetExitCodeProcess(process, &mut status) == FALSE {
-                    CloseHandle(process);
+                    assert!(CloseHandle(process) != 0);
                     fail!("failure in GetExitCodeProcess: {}", os::last_os_error());
                 }
                 if status != STILL_ACTIVE {
-                    CloseHandle(process);
+                    assert!(CloseHandle(process) != 0);
                     return p::ExitStatus(status as int);
                 }
                 if WaitForSingleObject(process, INFINITE) == WAIT_FAILED {
-                    CloseHandle(process);
+                    assert!(CloseHandle(process) != 0);
                     fail!("failure in WaitForSingleObject: {}", os::last_os_error());
                 }
             }

src/libnative/io/timer_helper.rs

@@ -126,11 +126,11 @@ mod imp {
     }
 
     pub fn signal(handle: HANDLE) {
-        unsafe { SetEvent(handle); }
+        assert!(unsafe { SetEvent(handle) != 0 });
     }
 
     pub fn close(handle: HANDLE) {
-        unsafe { CloseHandle(handle); }
+        assert!(unsafe { CloseHandle(handle) != 0 });
     }
 
     extern "system" {

src/libnative/io/timer_other.rs

@@ -187,7 +187,7 @@ fn helper(input: libc::c_int, messages: Port<Req>) {
 
                 // drain the file descriptor
                 let mut buf = [0];
-                fd.inner_read(buf).unwrap();
+                assert_eq!(fd.inner_read(buf).unwrap(), 1);
             }
 
             -1 if os::errno() == libc::EINTR as int => {}
@@ -216,7 +216,8 @@ impl Timer {
     }
 
     pub fn sleep(ms: u64) {
-        unsafe { libc::usleep((ms * 1000) as libc::c_uint); }
+        // FIXME: this can fail because of EINTR, what do do?
+        let _ = unsafe { libc::usleep((ms * 1000) as libc::c_uint) };
     }
 
     fn inner(&mut self) -> ~Inner {

src/libnative/io/timer_timerfd.rs

@@ -96,7 +96,7 @@ fn helper(input: libc::c_int, messages: Port<Req>) {
             if fd == input {
                 let mut buf = [0, ..1];
                 // drain the input file descriptor of its input
-                FileDesc::new(fd, false).inner_read(buf).unwrap();
+                let _ = FileDesc::new(fd, false).inner_read(buf).unwrap();
                 incoming = true;
             } else {
                 let mut bits = [0, ..8];
@@ -104,7 +104,7 @@ fn helper(input: libc::c_int, messages: Port<Req>) {
                 //
                 // FIXME: should this perform a send() this number of
                 //      times?
-                FileDesc::new(fd, false).inner_read(bits).unwrap();
+                let _ = FileDesc::new(fd, false).inner_read(bits).unwrap();
                 let remove = {
                     match map.find(&fd).expect("fd unregistered") {
                         &(ref c, oneshot) => !c.try_send(()) || oneshot
@@ -166,7 +166,8 @@ impl Timer {
     }
 
     pub fn sleep(ms: u64) {
-        unsafe { libc::usleep((ms * 1000) as libc::c_uint); }
+        // FIXME: this can fail because of EINTR, what do do?
+        let _ = unsafe { libc::usleep((ms * 1000) as libc::c_uint) };
     }
 
     fn remove(&mut self) {

src/libnative/io/timer_win32.rs

@@ -62,8 +62,8 @@ fn helper(input: libc::HANDLE, messages: Port<Req>) {
                         c.send(());
                         match objs.iter().position(|&o| o == obj) {
                             Some(i) => {
-                                objs.remove(i);
-                                chans.remove(i - 1);
+                                drop(objs.remove(i));
+                                drop(chans.remove(i - 1));
                             }
                             None => {}
                         }
@@ -83,8 +83,8 @@ fn helper(input: libc::HANDLE, messages: Port<Req>) {
                 }
             };
             if remove {
-                objs.remove(idx as uint);
-                chans.remove(idx as uint - 1);
+                drop(objs.remove(idx as uint));
+                drop(chans.remove(idx as uint - 1));
             }
         }
     }
@@ -133,7 +133,7 @@ impl rtio::RtioTimer for Timer {
                                   ptr::mut_null(), 0)
         }, 1);
 
-        unsafe { imp::WaitForSingleObject(self.obj, libc::INFINITE); }
+        let _ = unsafe { imp::WaitForSingleObject(self.obj, libc::INFINITE) };
     }
 
     fn oneshot(&mut self, msecs: u64) -> Port<()> {
@@ -173,7 +173,7 @@ impl rtio::RtioTimer for Timer {
 impl Drop for Timer {
     fn drop(&mut self) {
         self.remove();
-        unsafe { libc::CloseHandle(self.obj); }
+        assert!(unsafe { libc::CloseHandle(self.obj) != 0 });
     }
 }
 

src/libnative/lib.rs

@@ -21,6 +21,7 @@
 #[doc(html_logo_url = "http://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
       html_favicon_url = "http://www.rust-lang.org/favicon.ico",
       html_root_url = "http://static.rust-lang.org/doc/master")];
+#[deny(unused_result, unused_must_use)];
 
 // NB this crate explicitly does *not* allow glob imports, please seriously
 //    consider whether they're needed before adding that feature here (the
@@ -61,9 +62,10 @@ pub fn start(argc: int, argv: **u8, main: proc()) -> int {
     rt::init(argc, argv);
     let mut exit_code = None;
     let mut main = Some(main);
-    task::new((my_stack_bottom, my_stack_top)).run(|| {
+    let t = task::new((my_stack_bottom, my_stack_top)).run(|| {
         exit_code = Some(run(main.take_unwrap()));
     });
+    drop(t);
     unsafe { rt::cleanup(); }
     // If the exit code wasn't set, then the task block must have failed.
     return exit_code.unwrap_or(rt::DEFAULT_ERROR_CODE);

src/libnative/task.rs

@@ -103,7 +103,8 @@ pub fn spawn_opts(opts: TaskOpts, f: proc()) {
         let mut f = Some(f);
         let mut task = task;
         task.put_runtime(ops as ~rt::Runtime);
-        task.run(|| { f.take_unwrap()() });
+        let t = task.run(|| { f.take_unwrap()() });
+        drop(t);
         bookkeeping::decrement();
     })
 }

src/librustc/back/archive.rs

@@ -17,6 +17,7 @@ use lib::llvm::{ArchiveRef, llvm};
 
 use std::cast;
 use std::io::fs;
+use std::io;
 use std::libc;
 use std::os;
 use std::run::{ProcessOptions, Process, ProcessOutput};
@@ -50,9 +51,8 @@ fn run_ar(sess: Session, args: &str, cwd: Option<&Path>,
         Some(p) => { debug!("inside {}", p.display()); }
         None => {}
     }
-    let mut opt_prog = Process::new(ar, args.as_slice(), opts);
-    match opt_prog {
-        Some(ref mut prog) => {
+    match Process::new(ar, args.as_slice(), opts) {
+        Ok(mut prog) => {
             let o = prog.finish_with_output();
             if !o.status.success() {
                 sess.err(format!("{} {} failed with: {}", ar, args.connect(" "),
@@ -63,8 +63,8 @@ fn run_ar(sess: Session, args: &str, cwd: Option<&Path>,
             }
             o
         },
-        None => {
-            sess.err(format!("could not exec `{}`", ar));
+        Err(e) => {
+            sess.err(format!("could not exec `{}`: {}", ar, e));
             sess.abort_if_errors();
             fail!("rustc::back::archive::run_ar() should not reach this point");
         }
@@ -94,7 +94,7 @@ impl Archive {
             let archive = os::make_absolute(&self.dst);
             run_ar(self.sess, "x", Some(loc.path()), [&archive,
                                                       &Path::new(file)]);
-            fs::File::open(&loc.path().join(file)).read_to_end()
+            fs::File::open(&loc.path().join(file)).read_to_end().unwrap()
         } else {
             run_ar(self.sess, "p", None, [&self.dst, &Path::new(file)]).output
         }
@@ -102,9 +102,9 @@ impl Archive {
 
     /// Adds all of the contents of a native library to this archive. This will
     /// search in the relevant locations for a library named `name`.
-    pub fn add_native_library(&mut self, name: &str) {
+    pub fn add_native_library(&mut self, name: &str) -> io::IoResult<()> {
         let location = self.find_library(name);
-        self.add_archive(&location, name, []);
+        self.add_archive(&location, name, [])
     }
 
     /// Adds all of the contents of the rlib at the specified path to this
@@ -112,14 +112,15 @@ impl Archive {
     ///
     /// This ignores adding the bytecode from the rlib, and if LTO is enabled
     /// then the object file also isn't added.
-    pub fn add_rlib(&mut self, rlib: &Path, name: &str, lto: bool) {
+    pub fn add_rlib(&mut self, rlib: &Path, name: &str,
+                    lto: bool) -> io::IoResult<()> {
         let object = format!("{}.o", name);
         let bytecode = format!("{}.bc", name);
         let mut ignore = ~[METADATA_FILENAME, bytecode.as_slice()];
         if lto {
             ignore.push(object.as_slice());
         }
-        self.add_archive(rlib, name, ignore);
+        self.add_archive(rlib, name, ignore)
     }
 
     /// Adds an arbitrary file to this archive
@@ -144,7 +145,8 @@ impl Archive {
         str::from_utf8(output.output).unwrap().lines().map(|s| s.to_owned()).collect()
     }
 
-    fn add_archive(&mut self, archive: &Path, name: &str, skip: &[&str]) {
+    fn add_archive(&mut self, archive: &Path, name: &str,
+                   skip: &[&str]) -> io::IoResult<()> {
         let loc = TempDir::new("rsar").unwrap();
 
         // First, extract the contents of the archive to a temporary directory
@@ -159,7 +161,7 @@ impl Archive {
         // We skip any files explicitly desired for skipping, and we also skip
         // all SYMDEF files as these are just magical placeholders which get
         // re-created when we make a new archive anyway.
-        let files = fs::readdir(loc.path());
+        let files = if_ok!(fs::readdir(loc.path()));
         let mut inputs = ~[];
         for file in files.iter() {
             let filename = file.filename_str().unwrap();
@@ -168,7 +170,7 @@ impl Archive {
 
             let filename = format!("r-{}-{}", name, filename);
             let new_filename = file.with_filename(filename);
-            fs::rename(file, &new_filename);
+            if_ok!(fs::rename(file, &new_filename));
             inputs.push(new_filename);
         }
 
@@ -176,6 +178,7 @@ impl Archive {
         let mut args = ~[&self.dst];
         args.extend(&mut inputs.iter());
         run_ar(self.sess, "r", None, args.as_slice());
+        Ok(())
     }
 
     fn find_library(&self, name: &str) -> Path {

src/librustc/back/link.rs

@@ -100,7 +100,6 @@ pub mod write {
     use util::common::time;
 
     use std::c_str::ToCStr;
-    use std::io;
     use std::libc::{c_uint, c_int};
     use std::path::Path;
     use std::run;
@@ -297,12 +296,8 @@ pub mod write {
             assembly.as_str().unwrap().to_owned()];
 
         debug!("{} '{}'", cc, args.connect("' '"));
-        let opt_prog = {
-            let _guard = io::ignore_io_error();
-            run::process_output(cc, args)
-        };
-        match opt_prog {
-            Some(prog) => {
+        match run::process_output(cc, args) {
+            Ok(prog) => {
                 if !prog.status.success() {
                     sess.err(format!("linking with `{}` failed: {}", cc, prog.status));
                     sess.note(format!("{} arguments: '{}'", cc, args.connect("' '")));
@@ -310,8 +305,8 @@ pub mod write {
                     sess.abort_if_errors();
                 }
             },
-            None => {
-                sess.err(format!("could not exec the linker `{}`", cc));
+            Err(e) => {
+                sess.err(format!("could not exec the linker `{}`: {}", cc, e));
                 sess.abort_if_errors();
             }
         }
@@ -768,6 +763,15 @@ fn get_system_tool(sess: Session, tool: &str) -> ~str {
     }
 }
 
+fn remove(sess: Session, path: &Path) {
+    match fs::unlink(path) {
+        Ok(..) => {}
+        Err(e) => {
+            sess.err(format!("failed to remove {}: {}", path.display(), e));
+        }
+    }
+}
+
 /// Perform the linkage portion of the compilation phase. This will generate all
 /// of the requested outputs for this compilation session.
 pub fn link_binary(sess: Session,
@@ -785,17 +789,15 @@ pub fn link_binary(sess: Session,
 
     // Remove the temporary object file and metadata if we aren't saving temps
     if !sess.opts.save_temps {
-        fs::unlink(obj_filename);
-        fs::unlink(&obj_filename.with_extension("metadata.o"));
+        remove(sess, obj_filename);
+        remove(sess, &obj_filename.with_extension("metadata.o"));
     }
 
     out_filenames
 }
 
 fn is_writeable(p: &Path) -> bool {
-    use std::io;
-
-    match io::result(|| p.stat()) {
+    match p.stat() {
         Err(..) => true,
         Ok(m) => m.perm & io::UserWrite == io::UserWrite
     }
@@ -884,7 +886,7 @@ fn link_rlib(sess: Session,
     for &(ref l, kind) in used_libraries.get().iter() {
         match kind {
             cstore::NativeStatic => {
-                a.add_native_library(l.as_slice());
+                a.add_native_library(l.as_slice()).unwrap();
             }
             cstore::NativeFramework | cstore::NativeUnknown => {}
         }
@@ -919,16 +921,23 @@ fn link_rlib(sess: Session,
             // the same filename for metadata (stomping over one another)
             let tmpdir = TempDir::new("rustc").expect("needs a temp dir");
             let metadata = tmpdir.path().join(METADATA_FILENAME);
-            fs::File::create(&metadata).write(trans.metadata);
+            match fs::File::create(&metadata).write(trans.metadata) {
+                Ok(..) => {}
+                Err(e) => {
+                    sess.err(format!("failed to write {}: {}",
+                                     metadata.display(), e));
+                    sess.abort_if_errors();
+                }
+            }
             a.add_file(&metadata, false);
-            fs::unlink(&metadata);
+            remove(sess, &metadata);
 
             // For LTO purposes, the bytecode of this library is also inserted
             // into the archive.
             let bc = obj_filename.with_extension("bc");
             a.add_file(&bc, false);
             if !sess.opts.save_temps {
-                fs::unlink(&bc);
+                remove(sess, &bc);
             }
 
             // After adding all files to the archive, we need to update the
@@ -959,7 +968,7 @@ fn link_rlib(sess: Session,
 // metadata file).
 fn link_staticlib(sess: Session, obj_filename: &Path, out_filename: &Path) {
     let mut a = link_rlib(sess, None, obj_filename, out_filename);
-    a.add_native_library("morestack");
+    a.add_native_library("morestack").unwrap();
 
     let crates = sess.cstore.get_used_crates(cstore::RequireStatic);
     for &(cnum, ref path) in crates.iter() {
@@ -970,7 +979,7 @@ fn link_staticlib(sess: Session, obj_filename: &Path, out_filename: &Path) {
                 continue
             }
         };
-        a.add_rlib(&p, name, sess.lto());
+        a.add_rlib(&p, name, sess.lto()).unwrap();
         let native_libs = csearch::get_native_libraries(sess.cstore, cnum);
         for &(kind, ref lib) in native_libs.iter() {
             let name = match kind {
@@ -1004,14 +1013,10 @@ fn link_natively(sess: Session, dylib: bool, obj_filename: &Path,
 
     // Invoke the system linker
     debug!("{} {}", cc_prog, cc_args.connect(" "));
-    let opt_prog = {
-        let _guard = io::ignore_io_error();
-        time(sess.time_passes(), "running linker", (), |()|
-             run::process_output(cc_prog, cc_args))
-    };
-
-    match opt_prog {
-        Some(prog) => {
+    let prog = time(sess.time_passes(), "running linker", (), |()|
+                    run::process_output(cc_prog, cc_args));
+    match prog {
+        Ok(prog) => {
             if !prog.status.success() {
                 sess.err(format!("linking with `{}` failed: {}", cc_prog, prog.status));
                 sess.note(format!("{} arguments: '{}'", cc_prog, cc_args.connect("' '")));
@@ -1019,8 +1024,8 @@ fn link_natively(sess: Session, dylib: bool, obj_filename: &Path,
                 sess.abort_if_errors();
             }
         },
-        None => {
-            sess.err(format!("could not exec the linker `{}`", cc_prog));
+        Err(e) => {
+            sess.err(format!("could not exec the linker `{}`: {}", cc_prog, e));
             sess.abort_if_errors();
         }
     }
@@ -1030,8 +1035,14 @@ fn link_natively(sess: Session, dylib: bool, obj_filename: &Path,
     // the symbols
     if sess.targ_cfg.os == abi::OsMacos && sess.opts.debuginfo {
         // FIXME (#9639): This needs to handle non-utf8 paths
-        run::process_status("dsymutil",
-                            [out_filename.as_str().unwrap().to_owned()]);
+        match run::process_status("dsymutil",
+                                  [out_filename.as_str().unwrap().to_owned()]) {
+            Ok(..) => {}
+            Err(e) => {
+                sess.err(format!("failed to run dsymutil: {}", e));
+                sess.abort_if_errors();
+            }
+        }
     }
 }
 
@@ -1225,7 +1236,16 @@ fn add_upstream_rust_crates(args: &mut ~[~str], sess: Session,
                     time(sess.time_passes(), format!("altering {}.rlib", name),
                          (), |()| {
                         let dst = tmpdir.join(cratepath.filename().unwrap());
-                        fs::copy(&cratepath, &dst);
+                        match fs::copy(&cratepath, &dst) {
+                            Ok(..) => {}
+                            Err(e) => {
+                                sess.err(format!("failed to copy {} to {}: {}",
+                                                 cratepath.display(),
+                                                 dst.display(),
+                                                 e));
+                                sess.abort_if_errors();
+                            }
+                        }
                         let dst_str = dst.as_str().unwrap().to_owned();
                         let mut archive = Archive::open(sess, dst);
                         archive.remove_file(format!("{}.o", name));

src/librustc/driver/driver.rs

@@ -399,7 +399,7 @@ pub fn phase_5_run_llvm_passes(sess: Session,
 
         // Remove assembly source, unless --save-temps was specified
         if !sess.opts.save_temps {
-            fs::unlink(&asm_filename);
+            fs::unlink(&asm_filename).unwrap();
         }
     } else {
         time(sess.time_passes(), "LLVM passes", (), |_|
@@ -455,33 +455,39 @@ pub fn stop_after_phase_5(sess: Session) -> bool {
     return false;
 }
 
-fn write_out_deps(sess: Session, input: &Input, outputs: &OutputFilenames, crate: &ast::Crate)
+fn write_out_deps(sess: Session, input: &Input, outputs: &OutputFilenames,
+                  crate: &ast::Crate) -> io::IoResult<()>
 {
     let lm = link::build_link_meta(sess, crate.attrs, &outputs.obj_filename,
-                                       &mut ::util::sha2::Sha256::new());
+                                   &mut ::util::sha2::Sha256::new());
 
     let sess_outputs = sess.outputs.borrow();
     let out_filenames = sess_outputs.get().iter()
-        .map(|&output| link::filename_for_input(&sess, output, &lm, &outputs.out_filename))
+        .map(|&output| link::filename_for_input(&sess, output, &lm,
+                                                &outputs.out_filename))
         .to_owned_vec();
 
-    // Write out dependency rules to the dep-info file if requested with --dep-info
+    // Write out dependency rules to the dep-info file if requested with
+    // --dep-info
     let deps_filename = match sess.opts.write_dependency_info {
         // Use filename from --dep-file argument if given
         (true, Some(ref filename)) => filename.clone(),
-        // Use default filename: crate source filename with extension replaced by ".d"
+        // Use default filename: crate source filename with extension replaced
+        // by ".d"
         (true, None) => match *input {
             FileInput(ref input_path) => {
-                let filestem = input_path.filestem().expect("input file must have stem");
-                let filename = out_filenames[0].dir_path().join(filestem).with_extension("d");
-                filename
+                let filestem = input_path.filestem().expect("input file must \
+                                                             have stem");
+                let filename = out_filenames[0].dir_path().join(filestem);
+                filename.with_extension("d")
             },
             StrInput(..) => {
-                sess.warn("can not write --dep-info without a filename when compiling stdin.");
-                return;
+                sess.warn("can not write --dep-info without a filename \
+                           when compiling stdin.");
+                return Ok(());
             },
         },
-        _ => return,
+        _ => return Ok(()),
     };
 
     // Build a list of files used to compile the output and
@@ -499,11 +505,12 @@ fn write_out_deps(sess: Session, input: &Input, outputs: &OutputFilenames, crate
              })
              .collect()
     };
-    let mut file = io::File::create(&deps_filename);
+    let mut file = if_ok!(io::File::create(&deps_filename));
     for path in out_filenames.iter() {
-        write!(&mut file as &mut Writer,
-               "{}: {}\n\n", path.display(), files.connect(" "));
+        if_ok!(write!(&mut file as &mut Writer,
+                      "{}: {}\n\n", path.display(), files.connect(" ")));
     }
+    Ok(())
 }
 
 pub fn compile_input(sess: Session, cfg: ast::CrateConfig, input: &Input,
@@ -521,7 +528,7 @@ pub fn compile_input(sess: Session, cfg: ast::CrateConfig, input: &Input,
         let outputs = build_output_filenames(input, outdir, output,
                                              expanded_crate.attrs, sess);
 
-        write_out_deps(sess, input, outputs, &expanded_crate);
+        write_out_deps(sess, input, outputs, &expanded_crate).unwrap();
 
         if stop_after_phase_2(sess) { return; }
 
@@ -541,32 +548,33 @@ struct IdentifiedAnnotation {
 }
 
 impl pprust::PpAnn for IdentifiedAnnotation {
-    fn pre(&self, node: pprust::AnnNode) {
+    fn pre(&self, node: pprust::AnnNode) -> io::IoResult<()> {
         match node {
             pprust::NodeExpr(s, _) => pprust::popen(s),
-            _ => ()
+            _ => Ok(())
         }
     }
-    fn post(&self, node: pprust::AnnNode) {
+    fn post(&self, node: pprust::AnnNode) -> io::IoResult<()> {
         match node {
             pprust::NodeItem(s, item) => {
-                pp::space(&mut s.s);
-                pprust::synth_comment(s, item.id.to_str());
+                if_ok!(pp::space(&mut s.s));
+                if_ok!(pprust::synth_comment(s, item.id.to_str()));
             }
             pprust::NodeBlock(s, blk) => {
-                pp::space(&mut s.s);
-                pprust::synth_comment(s, ~"block " + blk.id.to_str());
+                if_ok!(pp::space(&mut s.s));
+                if_ok!(pprust::synth_comment(s, ~"block " + blk.id.to_str()));
             }
             pprust::NodeExpr(s, expr) => {
-                pp::space(&mut s.s);
-                pprust::synth_comment(s, expr.id.to_str());
-                pprust::pclose(s);
+                if_ok!(pp::space(&mut s.s));
+                if_ok!(pprust::synth_comment(s, expr.id.to_str()));
+                if_ok!(pprust::pclose(s));
             }
             pprust::NodePat(s, pat) => {
-                pp::space(&mut s.s);
-                pprust::synth_comment(s, ~"pat " + pat.id.to_str());
+                if_ok!(pp::space(&mut s.s));
+                if_ok!(pprust::synth_comment(s, ~"pat " + pat.id.to_str()));
             }
         }
+        Ok(())
     }
 }
 
@@ -575,24 +583,26 @@ struct TypedAnnotation {
 }
 
 impl pprust::PpAnn for TypedAnnotation {
-    fn pre(&self, node: pprust::AnnNode) {
+    fn pre(&self, node: pprust::AnnNode) -> io::IoResult<()> {
         match node {
             pprust::NodeExpr(s, _) => pprust::popen(s),
-            _ => ()
+            _ => Ok(())
         }
     }
-    fn post(&self, node: pprust::AnnNode) {
+    fn post(&self, node: pprust::AnnNode) -> io::IoResult<()> {
         let tcx = self.analysis.ty_cx;
         match node {
             pprust::NodeExpr(s, expr) => {
-                pp::space(&mut s.s);
-                pp::word(&mut s.s, "as");
-                pp::space(&mut s.s);
-                pp::word(&mut s.s, ppaux::ty_to_str(tcx, ty::expr_ty(tcx, expr)));
-                pprust::pclose(s);
+                if_ok!(pp::space(&mut s.s));
+                if_ok!(pp::word(&mut s.s, "as"));
+                if_ok!(pp::space(&mut s.s));
+                if_ok!(pp::word(&mut s.s,
+                                ppaux::ty_to_str(tcx, ty::expr_ty(tcx, expr))));
+                if_ok!(pprust::pclose(s));
             }
             _ => ()
         }
+        Ok(())
     }
 }
 
@@ -638,7 +648,7 @@ pub fn pretty_print_input(sess: Session,
                         &mut rdr,
                         ~stdout as ~io::Writer,
                         annotation,
-                        is_expanded);
+                        is_expanded).unwrap();
 }
 
 pub fn get_os(triple: &str) -> Option<abi::Os> {
@@ -1167,10 +1177,11 @@ pub fn early_error(emitter: &diagnostic::Emitter, msg: &str) -> ! {
     fail!(diagnostic::FatalError);
 }
 
-pub fn list_metadata(sess: Session, path: &Path, out: &mut io::Writer) {
+pub fn list_metadata(sess: Session, path: &Path,
+                     out: &mut io::Writer) -> io::IoResult<()> {
     metadata::loader::list_file_metadata(
         token::get_ident_interner(),
-        session::sess_os_to_meta_os(sess.targ_cfg.os), path, out);
+        session::sess_os_to_meta_os(sess.targ_cfg.os), path, out)
 }
 
 #[cfg(test)]

src/librustc/lib.rs

@@ -54,6 +54,11 @@ use syntax::diagnostic::Emitter;
 use syntax::diagnostic;
 use syntax::parse;
 
+#[cfg(stage0)]
+macro_rules! if_ok (
+    ($e:expr) => (match $e { Ok(e) => e, Err(e) => return Err(e) })
+)
+
 pub mod middle {
     pub mod trans;
     pub mod ty;
@@ -236,8 +241,8 @@ pub fn run_compiler(args: &[~str], demitter: @diagnostic::Emitter) {
       1u => {
         let ifile = matches.free[0].as_slice();
         if ifile == "-" {
-            let src =
-                str::from_utf8_owned(io::stdin().read_to_end()).unwrap();
+            let contents = io::stdin().read_to_end().unwrap();
+            let src = str::from_utf8_owned(contents).unwrap();
             (d::StrInput(src), None)
         } else {
             (d::FileInput(Path::new(ifile)), Some(Path::new(ifile)))
@@ -267,7 +272,7 @@ pub fn run_compiler(args: &[~str], demitter: @diagnostic::Emitter) {
           d::FileInput(ref ifile) => {
             let mut stdout = io::stdout();
             d::list_metadata(sess, &(*ifile),
-                                  &mut stdout as &mut io::Writer);
+                             &mut stdout as &mut io::Writer).unwrap();
           }
           d::StrInput(_) => {
             d::early_error(demitter, "can not list metadata for stdin");

src/librustc/metadata/decoder.rs

@@ -1111,15 +1111,15 @@ fn get_attributes(md: ebml::Doc) -> ~[ast::Attribute] {
 }
 
 fn list_crate_attributes(intr: @IdentInterner, md: ebml::Doc, hash: &str,
-                         out: &mut io::Writer) {
-    write!(out, "=Crate Attributes ({})=\n", hash);
+                         out: &mut io::Writer) -> io::IoResult<()> {
+    if_ok!(write!(out, "=Crate Attributes ({})=\n", hash));
 
     let r = get_attributes(md);
     for attr in r.iter() {
-        write!(out, "{}\n", pprust::attribute_to_str(attr, intr));
+        if_ok!(write!(out, "{}\n", pprust::attribute_to_str(attr, intr)));
     }
 
-    write!(out, "\n\n");
+    write!(out, "\n\n")
 }
 
 pub fn get_crate_attributes(data: &[u8]) -> ~[ast::Attribute] {
@@ -1154,21 +1154,22 @@ pub fn get_crate_deps(data: &[u8]) -> ~[CrateDep] {
     return deps;
 }
 
-fn list_crate_deps(data: &[u8], out: &mut io::Writer) {
-    write!(out, "=External Dependencies=\n");
+fn list_crate_deps(data: &[u8], out: &mut io::Writer) -> io::IoResult<()> {
+    if_ok!(write!(out, "=External Dependencies=\n"));
 
     let r = get_crate_deps(data);
     for dep in r.iter() {
         let string = token::get_ident(dep.name.name);
-        write!(out,
-               "{} {}-{}-{}\n",
-               dep.cnum,
-               string.get(),
-               dep.hash,
-               dep.vers);
+        if_ok!(write!(out,
+                      "{} {}-{}-{}\n",
+                      dep.cnum,
+                      string.get(),
+                      dep.hash,
+                      dep.vers));
     }
 
-    write!(out, "\n");
+    if_ok!(write!(out, "\n"));
+    Ok(())
 }
 
 pub fn get_crate_hash(data: &[u8]) -> ~str {
@@ -1186,11 +1187,11 @@ pub fn get_crate_vers(data: &[u8]) -> ~str {
 }
 
 pub fn list_crate_metadata(intr: @IdentInterner, bytes: &[u8],
-                           out: &mut io::Writer) {
+                           out: &mut io::Writer) -> io::IoResult<()> {
     let hash = get_crate_hash(bytes);
     let md = reader::Doc(bytes);
-    list_crate_attributes(intr, md, hash, out);
-    list_crate_deps(bytes, out);
+    if_ok!(list_crate_attributes(intr, md, hash, out));
+    list_crate_deps(bytes, out)
 }
 
 // Translates a def_id from an external crate to a def_id for the current

src/librustc/metadata/encoder.rs

@@ -10,6 +10,7 @@
 
 // Metadata encoding
 
+#[allow(unused_must_use)]; // everything is just a MemWriter, can't fail
 
 use metadata::common::*;
 use metadata::cstore;
@@ -350,7 +351,7 @@ fn encode_enum_variant_info(ecx: &EncodeContext,
             let mut index = index.borrow_mut();
             index.get().push(entry {
                 val: variant.node.id as i64,
-                pos: ebml_w.writer.tell(),
+                pos: ebml_w.writer.tell().unwrap(),
             });
         }
         ebml_w.start_tag(tag_items_data_item);
@@ -668,10 +669,10 @@ fn encode_explicit_self(ebml_w: &mut writer::Encoder, explicit_self: ast::Explic
 
     // Encode the base self type.
     match explicit_self {
-        SelfStatic => ebml_w.writer.write(&[ 's' as u8 ]),
-        SelfValue  => ebml_w.writer.write(&[ 'v' as u8 ]),
-        SelfBox    => ebml_w.writer.write(&[ '@' as u8 ]),
-        SelfUniq   => ebml_w.writer.write(&[ '~' as u8 ]),
+        SelfStatic => { ebml_w.writer.write(&[ 's' as u8 ]); }
+        SelfValue  => { ebml_w.writer.write(&[ 'v' as u8 ]); }
+        SelfBox    => { ebml_w.writer.write(&[ '@' as u8 ]); }
+        SelfUniq   => { ebml_w.writer.write(&[ '~' as u8 ]); }
         SelfRegion(_, m) => {
             // FIXME(#4846) encode custom lifetime
             ebml_w.writer.write(&['&' as u8]);
@@ -684,8 +685,8 @@ fn encode_explicit_self(ebml_w: &mut writer::Encoder, explicit_self: ast::Explic
     fn encode_mutability(ebml_w: &writer::Encoder,
                          m: ast::Mutability) {
         match m {
-            MutImmutable => ebml_w.writer.write(&[ 'i' as u8 ]),
-            MutMutable => ebml_w.writer.write(&[ 'm' as u8 ]),
+            MutImmutable => { ebml_w.writer.write(&[ 'i' as u8 ]); }
+            MutMutable => { ebml_w.writer.write(&[ 'm' as u8 ]); }
         }
     }
 }
@@ -726,12 +727,12 @@ fn encode_info_for_struct(ecx: &EncodeContext,
         };
 
         let id = field.node.id;
-        index.push(entry {val: id as i64, pos: ebml_w.writer.tell()});
+        index.push(entry {val: id as i64, pos: ebml_w.writer.tell().unwrap()});
         {
             let mut global_index = global_index.borrow_mut();
             global_index.get().push(entry {
                 val: id as i64,
-                pos: ebml_w.writer.tell(),
+                pos: ebml_w.writer.tell().unwrap(),
             });
         }
         ebml_w.start_tag(tag_items_data_item);
@@ -758,7 +759,7 @@ fn encode_info_for_struct_ctor(ecx: &EncodeContext,
         let mut index = index.borrow_mut();
         index.get().push(entry {
             val: ctor_id as i64,
-            pos: ebml_w.writer.tell(),
+            pos: ebml_w.writer.tell().unwrap(),
         });
     }
 
@@ -921,7 +922,7 @@ fn encode_info_for_item(ecx: &EncodeContext,
         let mut index = index.borrow_mut();
         index.get().push(entry {
             val: item.id as i64,
-            pos: ebml_w.writer.tell(),
+            pos: ebml_w.writer.tell().unwrap(),
         });
     }
     let add_to_index: || = || add_to_index(item, ebml_w, index);
@@ -1157,7 +1158,7 @@ fn encode_info_for_item(ecx: &EncodeContext,
                 let mut index = index.borrow_mut();
                 index.get().push(entry {
                     val: m.def_id.node as i64,
-                    pos: ebml_w.writer.tell(),
+                    pos: ebml_w.writer.tell().unwrap(),
                 });
             }
             encode_info_for_method(ecx,
@@ -1219,7 +1220,7 @@ fn encode_info_for_item(ecx: &EncodeContext,
                 let mut index = index.borrow_mut();
                 index.get().push(entry {
                     val: method_def_id.node as i64,
-                    pos: ebml_w.writer.tell(),
+                    pos: ebml_w.writer.tell().unwrap(),
                 });
             }
 
@@ -1294,7 +1295,7 @@ fn encode_info_for_foreign_item(ecx: &EncodeContext,
         let mut index = index.borrow_mut();
         index.get().push(entry {
             val: nitem.id as i64,
-            pos: ebml_w.writer.tell(),
+            pos: ebml_w.writer.tell().unwrap(),
         });
     }
 
@@ -1418,7 +1419,7 @@ fn encode_info_for_items(ecx: &EncodeContext,
         let mut index = index.borrow_mut();
         index.get().push(entry {
             val: CRATE_NODE_ID as i64,
-            pos: ebml_w.writer.tell(),
+            pos: ebml_w.writer.tell().unwrap(),
         });
     }
     encode_info_for_mod(ecx,
@@ -1478,7 +1479,7 @@ fn encode_index<T:'static>(
     let mut bucket_locs = ~[];
     ebml_w.start_tag(tag_index_buckets);
     for bucket in buckets.iter() {
-        bucket_locs.push(ebml_w.writer.tell());
+        bucket_locs.push(ebml_w.writer.tell().unwrap());
         ebml_w.start_tag(tag_index_buckets_bucket);
         for elt in (**bucket).iter() {
             ebml_w.start_tag(tag_index_buckets_bucket_elt);
@@ -1895,58 +1896,58 @@ fn encode_metadata_inner(wr: &mut MemWriter, parms: EncodeParams, crate: &Crate)
 
     encode_hash(&mut ebml_w, ecx.link_meta.crate_hash);
 
-    let mut i = ebml_w.writer.tell();
+    let mut i = ebml_w.writer.tell().unwrap();
     let crate_attrs = synthesize_crate_attrs(&ecx, crate);
     encode_attributes(&mut ebml_w, crate_attrs);
-    ecx.stats.attr_bytes.set(ebml_w.writer.tell() - i);
+    ecx.stats.attr_bytes.set(ebml_w.writer.tell().unwrap() - i);
 
-    i = ebml_w.writer.tell();
+    i = ebml_w.writer.tell().unwrap();
     encode_crate_deps(&ecx, &mut ebml_w, ecx.cstore);
-    ecx.stats.dep_bytes.set(ebml_w.writer.tell() - i);
+    ecx.stats.dep_bytes.set(ebml_w.writer.tell().unwrap() - i);
 
     // Encode the language items.
-    i = ebml_w.writer.tell();
+    i = ebml_w.writer.tell().unwrap();
     encode_lang_items(&ecx, &mut ebml_w);
-    ecx.stats.lang_item_bytes.set(ebml_w.writer.tell() - i);
+    ecx.stats.lang_item_bytes.set(ebml_w.writer.tell().unwrap() - i);
 
     // Encode the native libraries used
-    i = ebml_w.writer.tell();
+    i = ebml_w.writer.tell().unwrap();
     encode_native_libraries(&ecx, &mut ebml_w);
-    ecx.stats.native_lib_bytes.set(ebml_w.writer.tell() - i);
+    ecx.stats.native_lib_bytes.set(ebml_w.writer.tell().unwrap() - i);
 
     // Encode the macro registrar function
-    i = ebml_w.writer.tell();
+    i = ebml_w.writer.tell().unwrap();
     encode_macro_registrar_fn(&ecx, &mut ebml_w);
-    ecx.stats.macro_registrar_fn_bytes.set(ebml_w.writer.tell() - i);
+    ecx.stats.macro_registrar_fn_bytes.set(ebml_w.writer.tell().unwrap() - i);
 
     // Encode macro definitions
-    i = ebml_w.writer.tell();
+    i = ebml_w.writer.tell().unwrap();
     encode_macro_defs(&ecx, crate, &mut ebml_w);
-    ecx.stats.macro_defs_bytes.set(ebml_w.writer.tell() - i);
+    ecx.stats.macro_defs_bytes.set(ebml_w.writer.tell().unwrap() - i);
 
     // Encode the def IDs of impls, for coherence checking.
-    i = ebml_w.writer.tell();
+    i = ebml_w.writer.tell().unwrap();
     encode_impls(&ecx, crate, &mut ebml_w);
-    ecx.stats.impl_bytes.set(ebml_w.writer.tell() - i);
+    ecx.stats.impl_bytes.set(ebml_w.writer.tell().unwrap() - i);
 
     // Encode miscellaneous info.
-    i = ebml_w.writer.tell();
+    i = ebml_w.writer.tell().unwrap();
     encode_misc_info(&ecx, crate, &mut ebml_w);
-    ecx.stats.misc_bytes.set(ebml_w.writer.tell() - i);
+    ecx.stats.misc_bytes.set(ebml_w.writer.tell().unwrap() - i);
 
     // Encode and index the items.
     ebml_w.start_tag(tag_items);
-    i = ebml_w.writer.tell();
+    i = ebml_w.writer.tell().unwrap();
     let items_index = encode_info_for_items(&ecx, &mut ebml_w, crate);
-    ecx.stats.item_bytes.set(ebml_w.writer.tell() - i);
+    ecx.stats.item_bytes.set(ebml_w.writer.tell().unwrap() - i);
 
-    i = ebml_w.writer.tell();
+    i = ebml_w.writer.tell().unwrap();
     let items_buckets = create_index(items_index);
     encode_index(&mut ebml_w, items_buckets, write_i64);
-    ecx.stats.index_bytes.set(ebml_w.writer.tell() - i);
+    ecx.stats.index_bytes.set(ebml_w.writer.tell().unwrap() - i);
     ebml_w.end_tag();
 
-    ecx.stats.total_bytes.set(ebml_w.writer.tell());
+    ecx.stats.total_bytes.set(ebml_w.writer.tell().unwrap());
 
     if tcx.sess.meta_stats() {
         for e in ebml_w.writer.get_ref().iter() {

src/librustc/metadata/filesearch.rs

@@ -11,7 +11,6 @@
 use std::cell::RefCell;
 use std::option;
 use std::os;
-use std::io;
 use std::io::fs;
 use std::hashmap::HashSet;
 
@@ -93,7 +92,7 @@ impl FileSearch {
     pub fn search(&self, pick: pick) {
         self.for_each_lib_search_path(|lib_search_path| {
             debug!("searching {}", lib_search_path.display());
-            match io::result(|| fs::readdir(lib_search_path)) {
+            match fs::readdir(lib_search_path) {
                 Ok(files) => {
                     let mut rslt = FileDoesntMatch;
                     let is_rlib = |p: & &Path| {
@@ -163,8 +162,8 @@ pub fn get_or_default_sysroot() -> Path {
     // Follow symlinks.  If the resolved path is relative, make it absolute.
     fn canonicalize(path: Option<Path>) -> Option<Path> {
         path.and_then(|mut path|
-            match io::io_error::cond.trap(|_| ()).inside(|| fs::readlink(&path)) {
-                Some(canon) => {
+            match fs::readlink(&path) {
+                Ok(canon) => {
                     if canon.is_absolute() {
                         Some(canon)
                     } else {
@@ -172,7 +171,7 @@ pub fn get_or_default_sysroot() -> Path {
                         Some(path.join(canon))
                     }
                 },
-                None => Some(path),
+                Err(..) => Some(path),
             })
     }
 

src/librustc/metadata/loader.rs

@@ -381,13 +381,13 @@ pub fn read_meta_section_name(os: Os) -> &'static str {
 pub fn list_file_metadata(intr: @IdentInterner,
                           os: Os,
                           path: &Path,
-                          out: &mut io::Writer) {
+                          out: &mut io::Writer) -> io::IoResult<()> {
     match get_metadata_section(os, path) {
       option::Some(bytes) => decoder::list_crate_metadata(intr,
                                                           bytes.as_slice(),
                                                           out),
       option::None => {
-        write!(out, "could not find metadata in {}.\n", path.display())
+          write!(out, "could not find metadata in {}.\n", path.display())
       }
     }
 }

src/librustc/metadata/tyencode.rs

@@ -10,6 +10,8 @@
 
 // Type encoding
 
+#[allow(unused_must_use)]; // as with encoding, everything is a no-fail MemWriter
+
 use std::cell::RefCell;
 use std::hashmap::HashMap;
 use std::io;
@@ -92,9 +94,9 @@ pub fn enc_ty(w: &mut MemWriter, cx: @ctxt, t: ty::t) {
                   None => {}
               }
           }
-          let pos = w.tell();
+          let pos = w.tell().unwrap();
           enc_sty(w, cx, &ty::get(t).sty);
-          let end = w.tell();
+          let end = w.tell().unwrap();
           let len = end - pos;
           fn estimate_sz(u: u64) -> u64 {
               let mut n = u;

src/librustc/middle/dataflow.rs

@@ -88,7 +88,7 @@ struct LoopScope<'a> {
 }
 
 impl<O:DataFlowOperator> pprust::PpAnn for DataFlowContext<O> {
-    fn pre(&self, node: pprust::AnnNode) {
+    fn pre(&self, node: pprust::AnnNode) -> io::IoResult<()> {
         let (ps, id) = match node {
             pprust::NodeExpr(ps, expr) => (ps, expr.id),
             pprust::NodeBlock(ps, blk) => (ps, blk.id),
@@ -117,9 +117,10 @@ impl<O:DataFlowOperator> pprust::PpAnn for DataFlowContext<O> {
 
             let comment_str = format!("id {}: {}{}{}",
                                       id, entry_str, gens_str, kills_str);
-            pprust::synth_comment(ps, comment_str);
-            pp::space(&mut ps.s);
+            if_ok!(pprust::synth_comment(ps, comment_str));
+            if_ok!(pp::space(&mut ps.s));
         }
+        Ok(())
     }
 }
 
@@ -347,18 +348,20 @@ impl<O:DataFlowOperator+Clone+'static> DataFlowContext<O> {
         debug!("Dataflow result:");
         debug!("{}", {
             let this = @(*self).clone();
-            this.pretty_print_to(~io::stderr() as ~io::Writer, blk);
+            this.pretty_print_to(~io::stderr() as ~io::Writer, blk).unwrap();
             ""
         });
     }
 
-    fn pretty_print_to(@self, wr: ~io::Writer, blk: &ast::Block) {
+    fn pretty_print_to(@self, wr: ~io::Writer,
+                       blk: &ast::Block) -> io::IoResult<()> {
         let mut ps = pprust::rust_printer_annotated(wr, self.tcx.sess.intr(),
                                                     self as @pprust::PpAnn);
-        pprust::cbox(&mut ps, pprust::indent_unit);
-        pprust::ibox(&mut ps, 0u);
-        pprust::print_block(&mut ps, blk);
-        pp::eof(&mut ps.s);
+        if_ok!(pprust::cbox(&mut ps, pprust::indent_unit));
+        if_ok!(pprust::ibox(&mut ps, 0u));
+        if_ok!(pprust::print_block(&mut ps, blk));
+        if_ok!(pp::eof(&mut ps.s));
+        Ok(())
     }
 }
 

src/librustc/middle/liveness.rs

@@ -736,14 +736,15 @@ impl Liveness {
     pub fn write_vars(&self,
                       wr: &mut io::Writer,
                       ln: LiveNode,
-                      test: |uint| -> LiveNode) {
+                      test: |uint| -> LiveNode) -> io::IoResult<()> {
         let node_base_idx = self.idx(ln, Variable(0));
         for var_idx in range(0u, self.ir.num_vars.get()) {
             let idx = node_base_idx + var_idx;
             if test(idx).is_valid() {
-                write!(wr, " {}", Variable(var_idx).to_str());
+                if_ok!(write!(wr, " {}", Variable(var_idx).to_str()));
             }
         }
+        Ok(())
     }
 
     pub fn find_loop_scope(&self,
@@ -781,6 +782,7 @@ impl Liveness {
         *loop_scope.get().last().unwrap()
     }
 
+    #[allow(unused_must_use)]
     pub fn ln_str(&self, ln: LiveNode) -> ~str {
         let mut wr = io::MemWriter::new();
         {

src/librustdoc/html/escape.rs

@@ -20,7 +20,7 @@ use std::fmt;
 pub struct Escape<'a>(&'a str);
 
 impl<'a> fmt::Show for Escape<'a> {
-    fn fmt(s: &Escape<'a>, fmt: &mut fmt::Formatter) {
+    fn fmt(s: &Escape<'a>, fmt: &mut fmt::Formatter) -> fmt::Result {
         // Because the internet is always right, turns out there's not that many
         // characters to escape: http://stackoverflow.com/questions/7381974
         let Escape(s) = *s;
@@ -29,7 +29,7 @@ impl<'a> fmt::Show for Escape<'a> {
         for (i, ch) in s.bytes().enumerate() {
             match ch as char {
                 '<' | '>' | '&' | '\'' | '"' => {
-                    fmt.buf.write(pile_o_bits.slice(last, i).as_bytes());
+                    if_ok!(fmt.buf.write(pile_o_bits.slice(last, i).as_bytes()));
                     let s = match ch as char {
                         '>' => "&gt;",
                         '<' => "&lt;",
@@ -38,7 +38,7 @@ impl<'a> fmt::Show for Escape<'a> {
                         '"' => "&quot;",
                         _ => unreachable!()
                     };
-                    fmt.buf.write(s.as_bytes());
+                    if_ok!(fmt.buf.write(s.as_bytes()));
                     last = i + 1;
                 }
                 _ => {}
@@ -46,7 +46,8 @@ impl<'a> fmt::Show for Escape<'a> {
         }
 
         if last < s.len() {
-            fmt.buf.write(pile_o_bits.slice_from(last).as_bytes());
+            if_ok!(fmt.buf.write(pile_o_bits.slice_from(last).as_bytes()));
         }
+        Ok(())
     }
 }

src/librustdoc/html/format.rs

@@ -48,85 +48,104 @@ impl PuritySpace {
 }
 
 impl fmt::Show for clean::Generics {
-    fn fmt(g: &clean::Generics, f: &mut fmt::Formatter) {
-        if g.lifetimes.len() == 0 && g.type_params.len() == 0 { return }
-        f.buf.write("<".as_bytes());
+    fn fmt(g: &clean::Generics, f: &mut fmt::Formatter) -> fmt::Result {
+        if g.lifetimes.len() == 0 && g.type_params.len() == 0 { return Ok(()) }
+        if_ok!(f.buf.write("<".as_bytes()));
 
         for (i, life) in g.lifetimes.iter().enumerate() {
-            if i > 0 { f.buf.write(", ".as_bytes()); }
-            write!(f.buf, "{}", *life);
+            if i > 0 {
+                if_ok!(f.buf.write(", ".as_bytes()));
+            }
+            if_ok!(write!(f.buf, "{}", *life));
         }
 
         if g.type_params.len() > 0 {
-            if g.lifetimes.len() > 0 { f.buf.write(", ".as_bytes()); }
+            if g.lifetimes.len() > 0 {
+                if_ok!(f.buf.write(", ".as_bytes()));
+            }
 
             for (i, tp) in g.type_params.iter().enumerate() {
-                if i > 0 { f.buf.write(", ".as_bytes()) }
-                f.buf.write(tp.name.as_bytes());
+                if i > 0 {
+                    if_ok!(f.buf.write(", ".as_bytes()))
+                }
+                if_ok!(f.buf.write(tp.name.as_bytes()));
 
                 if tp.bounds.len() > 0 {
-                    f.buf.write(": ".as_bytes());
+                    if_ok!(f.buf.write(": ".as_bytes()));
                     for (i, bound) in tp.bounds.iter().enumerate() {
-                        if i > 0 { f.buf.write(" + ".as_bytes()); }
-                        write!(f.buf, "{}", *bound);
+                        if i > 0 {
+                            if_ok!(f.buf.write(" + ".as_bytes()));
+                        }
+                        if_ok!(write!(f.buf, "{}", *bound));
                     }
                 }
             }
         }
-        f.buf.write(">".as_bytes());
+        if_ok!(f.buf.write(">".as_bytes()));
+        Ok(())
     }
 }
 
 impl fmt::Show for clean::Lifetime {
-    fn fmt(l: &clean::Lifetime, f: &mut fmt::Formatter) {
-        f.buf.write("'".as_bytes());
-        f.buf.write(l.get_ref().as_bytes());
+    fn fmt(l: &clean::Lifetime, f: &mut fmt::Formatter) -> fmt::Result {
+        if_ok!(f.buf.write("'".as_bytes()));
+        if_ok!(f.buf.write(l.get_ref().as_bytes()));
+        Ok(())
     }
 }
 
 impl fmt::Show for clean::TyParamBound {
-    fn fmt(bound: &clean::TyParamBound, f: &mut fmt::Formatter) {
+    fn fmt(bound: &clean::TyParamBound, f: &mut fmt::Formatter) -> fmt::Result {
         match *bound {
             clean::RegionBound => {
                 f.buf.write("'static".as_bytes())
             }
             clean::TraitBound(ref ty) => {
-                write!(f.buf, "{}", *ty);
+                write!(f.buf, "{}", *ty)
             }
         }
     }
 }
 
 impl fmt::Show for clean::Path {
-    fn fmt(path: &clean::Path, f: &mut fmt::Formatter) {
-        if path.global { f.buf.write("::".as_bytes()) }
+    fn fmt(path: &clean::Path, f: &mut fmt::Formatter) -> fmt::Result {
+        if path.global {
+            if_ok!(f.buf.write("::".as_bytes()))
+        }
         for (i, seg) in path.segments.iter().enumerate() {
-            if i > 0 { f.buf.write("::".as_bytes()) }
-            f.buf.write(seg.name.as_bytes());
+            if i > 0 {
+                if_ok!(f.buf.write("::".as_bytes()))
+            }
+            if_ok!(f.buf.write(seg.name.as_bytes()));
 
             if seg.lifetimes.len() > 0 || seg.types.len() > 0 {
-                f.buf.write("<".as_bytes());
+                if_ok!(f.buf.write("<".as_bytes()));
                 let mut comma = false;
                 for lifetime in seg.lifetimes.iter() {
-                    if comma { f.buf.write(", ".as_bytes()); }
+                    if comma {
+                        if_ok!(f.buf.write(", ".as_bytes()));
+                    }
                     comma = true;
-                    write!(f.buf, "{}", *lifetime);
+                    if_ok!(write!(f.buf, "{}", *lifetime));
                 }
                 for ty in seg.types.iter() {
-                    if comma { f.buf.write(", ".as_bytes()); }
+                    if comma {
+                        if_ok!(f.buf.write(", ".as_bytes()));
+                    }
                     comma = true;
-                    write!(f.buf, "{}", *ty);
+                    if_ok!(write!(f.buf, "{}", *ty));
                 }
-                f.buf.write(">".as_bytes());
+                if_ok!(f.buf.write(">".as_bytes()));
             }
         }
+        Ok(())
     }
 }
 
 /// Used when rendering a `ResolvedPath` structure. This invokes the `path`
 /// rendering function with the necessary arguments for linking to a local path.
 fn resolved_path(w: &mut io::Writer, id: ast::NodeId, p: &clean::Path,
-                 print_all: bool) {
+                 print_all: bool) -> fmt::Result {
     path(w, p, print_all,
         |_cache, loc| { Some("../".repeat(loc.len())) },
         |cache| {
@@ -134,13 +153,14 @@ fn resolved_path(w: &mut io::Writer, id: ast::NodeId, p: &clean::Path,
                 None => None,
                 Some(&(ref fqp, shortty)) => Some((fqp.clone(), shortty))
             }
-        });
+        })
 }
 
 /// Used when rendering an `ExternalPath` structure. Like `resolved_path` this
 /// will invoke `path` with proper linking-style arguments.
 fn external_path(w: &mut io::Writer, p: &clean::Path, print_all: bool,
-                 fqn: &[~str], kind: clean::TypeKind, crate: ast::CrateNum) {
+                 fqn: &[~str], kind: clean::TypeKind,
+                 crate: ast::CrateNum) -> fmt::Result {
     path(w, p, print_all,
         |cache, loc| {
             match *cache.extern_locations.get(&crate) {
@@ -161,7 +181,9 @@ fn external_path(w: &mut io::Writer, p: &clean::Path, print_all: bool,
 
 fn path(w: &mut io::Writer, path: &clean::Path, print_all: bool,
         root: |&render::Cache, &[~str]| -> Option<~str>,
-        info: |&render::Cache| -> Option<(~[~str], &'static str)>) {
+        info: |&render::Cache| -> Option<(~[~str], &'static str)>)
+    -> fmt::Result
+{
     // The generics will get written to both the title and link
     let mut generics = ~"";
     let last = path.segments.last().unwrap();
@@ -200,20 +222,20 @@ fn path(w: &mut io::Writer, path: &clean::Path, print_all: bool,
                         let mut root = root;
                         for seg in path.segments.slice_to(amt).iter() {
                             if "super" == seg.name || "self" == seg.name {
-                                write!(w, "{}::", seg.name);
+                                if_ok!(write!(w, "{}::", seg.name));
                             } else {
                                 root.push_str(seg.name);
                                 root.push_str("/");
-                                write!(w, "<a class='mod'
-                                              href='{}index.html'>{}</a>::",
-                                       root,
-                                       seg.name);
+                                if_ok!(write!(w, "<a class='mod'
+                                                    href='{}index.html'>{}</a>::",
+                                              root,
+                                              seg.name));
                             }
                         }
                     }
                     None => {
                         for seg in path.segments.slice_to(amt).iter() {
-                            write!(w, "{}::", seg.name);
+                            if_ok!(write!(w, "{}::", seg.name));
                         }
                     }
                 }
@@ -241,51 +263,57 @@ fn path(w: &mut io::Writer, path: &clean::Path, print_all: bool,
                         }
                     }
 
-                    write!(w, "<a class='{}' href='{}' title='{}'>{}</a>",
-                           shortty, url, fqp.connect("::"), last.name);
+                    if_ok!(write!(w, "<a class='{}' href='{}' title='{}'>{}</a>",
+                                  shortty, url, fqp.connect("::"), last.name));
                 }
 
                 _ => {
-                    write!(w, "{}", last.name);
+                    if_ok!(write!(w, "{}", last.name));
                 }
             }
-            write!(w, "{}", generics);
+            if_ok!(write!(w, "{}", generics));
+            Ok(())
         })
     })
 }
 
 /// Helper to render type parameters
-fn typarams(w: &mut io::Writer, typarams: &Option<~[clean::TyParamBound]>) {
+fn typarams(w: &mut io::Writer,
+            typarams: &Option<~[clean::TyParamBound]>) -> fmt::Result {
     match *typarams {
         Some(ref params) => {
-            write!(w, "&lt;");
+            if_ok!(write!(w, "&lt;"));
             for (i, param) in params.iter().enumerate() {
-                if i > 0 { write!(w, ", "); }
-                write!(w, "{}", *param);
+                if i > 0 {
+                    if_ok!(write!(w, ", "));
+                }
+                if_ok!(write!(w, "{}", *param));
             }
-            write!(w, "&gt;");
+            if_ok!(write!(w, "&gt;"));
+            Ok(())
         }
-        None => {}
+        None => Ok(())
     }
 }
 
 impl fmt::Show for clean::Type {
-    fn fmt(g: &clean::Type, f: &mut fmt::Formatter) {
+    fn fmt(g: &clean::Type, f: &mut fmt::Formatter) -> fmt::Result {
         match *g {
             clean::TyParamBinder(id) | clean::Generic(id) => {
                 local_data::get(cache_key, |cache| {
                     let m = cache.unwrap().get();
-                    f.buf.write(m.typarams.get(&id).as_bytes());
+                    f.buf.write(m.typarams.get(&id).as_bytes())
                 })
             }
             clean::ResolvedPath{id, typarams: ref tp, path: ref path} => {
-                resolved_path(f.buf, id, path, false);
-                typarams(f.buf, tp);
+                if_ok!(resolved_path(f.buf, id, path, false));
+                typarams(f.buf, tp)
             }
             clean::ExternalPath{path: ref path, typarams: ref tp,
                                 fqn: ref fqn, kind, crate} => {
-                external_path(f.buf, path, false, fqn.as_slice(), kind, crate);
-                typarams(f.buf, tp);
+                if_ok!(external_path(f.buf, path, false, fqn.as_slice(), kind,
+                                     crate))
+                typarams(f.buf, tp)
             }
             clean::Self(..) => f.buf.write("Self".as_bytes()),
             clean::Primitive(prim) => {
@@ -306,7 +334,7 @@ impl fmt::Show for clean::Type {
                     ast::TyBool => "bool",
                     ast::TyChar => "char",
                 };
-                f.buf.write(s.as_bytes());
+                f.buf.write(s.as_bytes())
             }
             clean::Closure(ref decl) => {
                 let region = match decl.region {
@@ -322,7 +350,7 @@ impl fmt::Show for clean::Type {
                            ast::ManagedSigil => format!("@{}fn({})", region, decl.decl.inputs),
                        },
                        arrow = match decl.decl.output { clean::Unit => "no", _ => "yes" },
-                       ret = decl.decl.output);
+                       ret = decl.decl.output)
                 // FIXME: where are bounds and lifetimes printed?!
             }
             clean::BareFunction(ref decl) => {
@@ -333,19 +361,21 @@ impl fmt::Show for clean::Type {
                            ref s => " " + *s + " ",
                        },
                        decl.generics,
-                       decl.decl);
+                       decl.decl)
             }
             clean::Tuple(ref typs) => {
-                f.buf.write("(".as_bytes());
+                if_ok!(f.buf.write("(".as_bytes()));
                 for (i, typ) in typs.iter().enumerate() {
-                    if i > 0 { f.buf.write(", ".as_bytes()) }
-                    write!(f.buf, "{}", *typ);
+                    if i > 0 {
+                        if_ok!(f.buf.write(", ".as_bytes()))
+                    }
+                    if_ok!(write!(f.buf, "{}", *typ));
                 }
-                f.buf.write(")".as_bytes());
+                f.buf.write(")".as_bytes())
             }
             clean::Vector(ref t) => write!(f.buf, "[{}]", **t),
             clean::FixedVector(ref t, ref s) => {
-                write!(f.buf, "[{}, ..{}]", **t, *s);
+                write!(f.buf, "[{}, ..{}]", **t, *s)
             }
             clean::String => f.buf.write("str".as_bytes()),
             clean::Bool => f.buf.write("bool".as_bytes()),
@@ -368,23 +398,23 @@ impl fmt::Show for clean::Type {
                            clean::Mutable => "mut ",
                            clean::Immutable => "",
                        },
-                       **ty);
+                       **ty)
             }
         }
     }
 }
 
 impl fmt::Show for clean::FnDecl {
-    fn fmt(d: &clean::FnDecl, f: &mut fmt::Formatter) {
+    fn fmt(d: &clean::FnDecl, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f.buf, "({args}){arrow, select, yes{ -&gt; {ret}} other{}}",
                args = d.inputs,
                arrow = match d.output { clean::Unit => "no", _ => "yes" },
-               ret = d.output);
+               ret = d.output)
     }
 }
 
 impl fmt::Show for ~[clean::Argument] {
-    fn fmt(inputs: &~[clean::Argument], f: &mut fmt::Formatter) {
+    fn fmt(inputs: &~[clean::Argument], f: &mut fmt::Formatter) -> fmt::Result {
         let mut args = ~"";
         for (i, input) in inputs.iter().enumerate() {
             if i > 0 { args.push_str(", "); }
@@ -393,12 +423,12 @@ impl fmt::Show for ~[clean::Argument] {
             }
             args.push_str(format!("{}", input.type_));
         }
-        f.buf.write(args.as_bytes());
+        f.buf.write(args.as_bytes())
     }
 }
 
 impl<'a> fmt::Show for Method<'a> {
-    fn fmt(m: &Method<'a>, f: &mut fmt::Formatter) {
+    fn fmt(m: &Method<'a>, f: &mut fmt::Formatter) -> fmt::Result {
         let Method(selfty, d) = *m;
         let mut args = ~"";
         match *selfty {
@@ -429,74 +459,79 @@ impl<'a> fmt::Show for Method<'a> {
         write!(f.buf, "({args}){arrow, select, yes{ -&gt; {ret}} other{}}",
                args = args,
                arrow = match d.output { clean::Unit => "no", _ => "yes" },
-               ret = d.output);
+               ret = d.output)
     }
 }
 
 impl fmt::Show for VisSpace {
-    fn fmt(v: &VisSpace, f: &mut fmt::Formatter) {
+    fn fmt(v: &VisSpace, f: &mut fmt::Formatter) -> fmt::Result {
         match v.get() {
-            Some(ast::Public) => { write!(f.buf, "pub "); }
-            Some(ast::Private) => { write!(f.buf, "priv "); }
-            Some(ast::Inherited) | None => {}
+            Some(ast::Public) => write!(f.buf, "pub "),
+            Some(ast::Private) => write!(f.buf, "priv "),
+            Some(ast::Inherited) | None => Ok(())
         }
     }
 }
 
 impl fmt::Show for PuritySpace {
-    fn fmt(p: &PuritySpace, f: &mut fmt::Formatter) {
+    fn fmt(p: &PuritySpace, f: &mut fmt::Formatter) -> fmt::Result {
         match p.get() {
             ast::UnsafeFn => write!(f.buf, "unsafe "),
             ast::ExternFn => write!(f.buf, "extern "),
-            ast::ImpureFn => {}
+            ast::ImpureFn => Ok(())
         }
     }
 }
 
 impl fmt::Show for clean::ViewPath {
-    fn fmt(v: &clean::ViewPath, f: &mut fmt::Formatter) {
+    fn fmt(v: &clean::ViewPath, f: &mut fmt::Formatter) -> fmt::Result {
         match *v {
             clean::SimpleImport(ref name, ref src) => {
                 if *name == src.path.segments.last().unwrap().name {
-                    write!(f.buf, "use {};", *src);
+                    write!(f.buf, "use {};", *src)
                 } else {
-                    write!(f.buf, "use {} = {};", *name, *src);
+                    write!(f.buf, "use {} = {};", *name, *src)
                 }
             }
             clean::GlobImport(ref src) => {
-                write!(f.buf, "use {}::*;", *src);
+                write!(f.buf, "use {}::*;", *src)
             }
             clean::ImportList(ref src, ref names) => {
-                write!(f.buf, "use {}::\\{", *src);
+                if_ok!(write!(f.buf, "use {}::\\{", *src));
                 for (i, n) in names.iter().enumerate() {
-                    if i > 0 { write!(f.buf, ", "); }
-                    write!(f.buf, "{}", *n);
+                    if i > 0 {
+                        if_ok!(write!(f.buf, ", "));
+                    }
+                    if_ok!(write!(f.buf, "{}", *n));
                 }
-                write!(f.buf, "\\};");
+                write!(f.buf, "\\};")
             }
         }
     }
 }
 
 impl fmt::Show for clean::ImportSource {
-    fn fmt(v: &clean::ImportSource, f: &mut fmt::Formatter) {
+    fn fmt(v: &clean::ImportSource, f: &mut fmt::Formatter) -> fmt::Result {
         match v.did {
             // FIXME: shouldn't be restricted to just local imports
             Some(did) if ast_util::is_local(did) => {
-                resolved_path(f.buf, did.node, &v.path, true);
+                resolved_path(f.buf, did.node, &v.path, true)
             }
             _ => {
                 for (i, seg) in v.path.segments.iter().enumerate() {
-                    if i > 0 { write!(f.buf, "::") }
-                    write!(f.buf, "{}", seg.name);
+                    if i > 0 {
+                        if_ok!(write!(f.buf, "::"))
+                    }
+                    if_ok!(write!(f.buf, "{}", seg.name));
                 }
+                Ok(())
             }
         }
     }
 }
 
 impl fmt::Show for clean::ViewListIdent {
-    fn fmt(v: &clean::ViewListIdent, f: &mut fmt::Formatter) {
+    fn fmt(v: &clean::ViewListIdent, f: &mut fmt::Formatter) -> fmt::Result {
         match v.source {
             // FIXME: shouldn't be limited to just local imports
             Some(did) if ast_util::is_local(did) => {
@@ -508,7 +543,7 @@ impl fmt::Show for clean::ViewListIdent {
                         types: ~[],
                     }]
                 };
-                resolved_path(f.buf, did.node, &path, false);
+                resolved_path(f.buf, did.node, &path, false)
             }
             _ => write!(f.buf, "{}", v.name),
         }

src/librustdoc/html/layout.rs

@@ -26,6 +26,7 @@ pub struct Page<'a> {
 
 pub fn render<T: fmt::Show, S: fmt::Show>(
     dst: &mut io::Writer, layout: &Layout, page: &Page, sidebar: &S, t: &T)
+    -> fmt::Result
 {
     write!(dst,
 "<!DOCTYPE html>
@@ -121,7 +122,7 @@ pub fn render<T: fmt::Show, S: fmt::Show>(
     favicon   = nonestr(layout.favicon),
     sidebar   = *sidebar,
     crate     = layout.crate,
-    );
+    )
 }
 
 fn nonestr<'a>(s: &'a str) -> &'a str {

src/librustdoc/html/markdown.rs

@@ -109,7 +109,7 @@ fn stripped_filtered_line<'a>(s: &'a str) -> Option<&'a str> {
     }
 }
 
-pub fn render(w: &mut io::Writer, s: &str) {
+pub fn render(w: &mut io::Writer, s: &str) -> fmt::Result {
     extern fn block(ob: *buf, text: *buf, lang: *buf, opaque: *libc::c_void) {
         unsafe {
             let my_opaque: &my_opaque = cast::transmute(opaque);
@@ -159,11 +159,12 @@ pub fn render(w: &mut io::Writer, s: &str) {
         sd_markdown_render(ob, s.as_ptr(), s.len() as libc::size_t, markdown);
         sd_markdown_free(markdown);
 
-        vec::raw::buf_as_slice((*ob).data, (*ob).size as uint, |buf| {
-            w.write(buf);
+        let ret = vec::raw::buf_as_slice((*ob).data, (*ob).size as uint, |buf| {
+            w.write(buf)
         });
 
         bufrelease(ob);
+        ret
     }
 }
 
@@ -210,10 +211,10 @@ pub fn find_testable_code(doc: &str, tests: &mut ::test::Collector) {
 }
 
 impl<'a> fmt::Show for Markdown<'a> {
-    fn fmt(md: &Markdown<'a>, fmt: &mut fmt::Formatter) {
+    fn fmt(md: &Markdown<'a>, fmt: &mut fmt::Formatter) -> fmt::Result {
         let Markdown(md) = *md;
         // This is actually common enough to special-case
-        if md.len() == 0 { return; }
-        render(fmt.buf, md.as_slice());
+        if md.len() == 0 { return Ok(()) }
+        render(fmt.buf, md.as_slice())
     }
 }

src/librustdoc/lib.rs

@@ -162,10 +162,16 @@ pub fn main_args(args: &[~str]) -> int {
     let output = matches.opt_str("o").map(|s| Path::new(s));
     match matches.opt_str("w") {
         Some(~"html") | None => {
-            html::render::run(crate, output.unwrap_or(Path::new("doc")))
+            match html::render::run(crate, output.unwrap_or(Path::new("doc"))) {
+                Ok(()) => {}
+                Err(e) => fail!("failed to generate documentation: {}", e),
+            }
         }
         Some(~"json") => {
-            json_output(crate, res, output.unwrap_or(Path::new("doc.json")))
+            match json_output(crate, res, output.unwrap_or(Path::new("doc.json"))) {
+                Ok(()) => {}
+                Err(e) => fail!("failed to write json: {}", e),
+            }
         }
         Some(s) => {
             println!("unknown output format: {}", s);
@@ -276,8 +282,8 @@ fn rust_input(cratefile: &str, matches: &getopts::Matches) -> Output {
 /// run over the deserialized output.
 fn json_input(input: &str) -> Result<Output, ~str> {
     let mut input = match File::open(&Path::new(input)) {
-        Some(f) => f,
-        None => return Err(format!("couldn't open {} for reading", input)),
+        Ok(f) => f,
+        Err(e) => return Err(format!("couldn't open {}: {}", input, e)),
     };
     match json::from_reader(&mut input) {
         Err(s) => Err(s.to_str()),
@@ -312,7 +318,8 @@ fn json_input(input: &str) -> Result<Output, ~str> {
 
 /// Outputs the crate/plugin json as a giant json blob at the specified
 /// destination.
-fn json_output(crate: clean::Crate, res: ~[plugins::PluginJson], dst: Path) {
+fn json_output(crate: clean::Crate, res: ~[plugins::PluginJson],
+               dst: Path) -> io::IoResult<()> {
     // {
     //   "schema": version,
     //   "crate": { parsed crate ... },
@@ -340,6 +347,7 @@ fn json_output(crate: clean::Crate, res: ~[plugins::PluginJson], dst: Path) {
     json.insert(~"crate", crate_json);
     json.insert(~"plugins", json::Object(plugins_json));
 
-    let mut file = File::create(&dst).unwrap();
-    json::Object(json).to_writer(&mut file);
+    let mut file = if_ok!(File::create(&dst));
+    if_ok!(json::Object(json).to_writer(&mut file));
+    Ok(())
 }

src/librustdoc/test.rs

@@ -127,8 +127,8 @@ fn runtest(test: &str, cratename: &str, libs: HashSet<Path>) {
     let exe = outdir.path().join("rust_out");
     let out = run::process_output(exe.as_str().unwrap(), []);
     match out {
-        None => fail!("couldn't run the test"),
-        Some(out) => {
+        Err(e) => fail!("couldn't run the test: {}", e),
+        Ok(out) => {
             if !out.status.success() {
                 fail!("test executable failed:\n{}",
                       str::from_utf8(out.error));

src/librustuv/file.rs

@@ -140,9 +140,9 @@ impl FsRequest {
             let mut paths = ~[];
             let path = CString::new(path.with_ref(|p| p), false);
             let parent = Path::new(path);
-            c_str::from_c_multistring(req.get_ptr() as *libc::c_char,
-                                      Some(req.get_result() as uint),
-                                      |rel| {
+            let _ = c_str::from_c_multistring(req.get_ptr() as *libc::c_char,
+                                              Some(req.get_result() as uint),
+                                              |rel| {
                 let p = rel.as_bytes();
                 paths.push(parent.join(p.slice_to(rel.len())));
             });
@@ -378,7 +378,8 @@ impl Drop for FileWatcher {
             rtio::CloseAsynchronously => {
                 unsafe {
                     let req = uvll::malloc_req(uvll::UV_FS);
-                    uvll::uv_fs_close(self.loop_.handle, req, self.fd, close_cb);
+                    assert_eq!(uvll::uv_fs_close(self.loop_.handle, req,
+                                                 self.fd, close_cb), 0);
                 }
 
                 extern fn close_cb(req: *uvll::uv_fs_t) {

src/librustuv/homing.rs

@@ -176,7 +176,7 @@ mod test {
         });
 
         let task = pool.task(TaskOpts::new(), proc() {
-            port.recv();
+            drop(port.recv());
         });
         pool.spawn_sched().send(sched::TaskFromFriend(task));
 
@@ -197,7 +197,7 @@ mod test {
             let listener = UdpWatcher::bind(local_loop(), addr2);
             chan.send((listener.unwrap(), addr1));
             let mut listener = UdpWatcher::bind(local_loop(), addr1).unwrap();
-            listener.sendto([1, 2, 3, 4], addr2);
+            listener.sendto([1, 2, 3, 4], addr2).unwrap();
         });
 
         let task = pool.task(TaskOpts::new(), proc() {

src/librustuv/idle.rs

@@ -52,7 +52,7 @@ impl IdleWatcher {
                 let data = uvll::get_data_for_uv_handle(handle);
                 let f: ~proc() = cast::transmute(data);
                 (*f)();
-                uvll::uv_idle_stop(handle);
+                assert_eq!(uvll::uv_idle_stop(handle), 0);
                 uvll::uv_close(handle, close_cb);
             }
         }
@@ -122,7 +122,7 @@ mod test {
                     }
                 }
             };
-            task.wake().map(|t| t.reawaken(true));
+            let _ = task.wake().map(|t| t.reawaken(true));
         }
     }
 

src/librustuv/lib.rs

@@ -40,6 +40,7 @@ via `close` and `delete` methods.
 #[crate_type = "dylib"];
 
 #[feature(macro_rules)];
+#[deny(unused_result, unused_must_use)];
 
 #[cfg(test)] extern mod green;
 
@@ -207,7 +208,7 @@ fn wait_until_woken_after(slot: *mut Option<BlockedTask>, f: ||) {
 
 fn wakeup(slot: &mut Option<BlockedTask>) {
     assert!(slot.is_some());
-    slot.take_unwrap().wake().map(|t| t.reawaken(true));
+    let _ = slot.take_unwrap().wake().map(|t| t.reawaken(true));
 }
 
 pub struct Request {
@@ -276,7 +277,7 @@ impl Loop {
     pub fn wrap(handle: *uvll::uv_loop_t) -> Loop { Loop { handle: handle } }
 
     pub fn run(&mut self) {
-        unsafe { uvll::uv_run(self.handle, uvll::RUN_DEFAULT) };
+        assert_eq!(unsafe { uvll::uv_run(self.handle, uvll::RUN_DEFAULT) }, 0);
     }
 
     pub fn close(&mut self) {

src/librustuv/macros.rs

@@ -33,14 +33,15 @@ pub fn dumb_println(args: &fmt::Arguments) {
 
     struct Stderr;
     impl io::Writer for Stderr {
-        fn write(&mut self, data: &[u8]) {
-            unsafe {
+        fn write(&mut self, data: &[u8]) -> io::IoResult<()> {
+            let _ = unsafe {
                 libc::write(libc::STDERR_FILENO,
                             data.as_ptr() as *libc::c_void,
-                            data.len() as libc::size_t);
-            }
+                            data.len() as libc::size_t)
+            };
+            Ok(()) // just ignore the errors
         }
     }
     let mut w = Stderr;
-    fmt::writeln(&mut w as &mut io::Writer, args);
+    let _ = fmt::writeln(&mut w as &mut io::Writer, args);
 }

src/librustuv/net.rs

@@ -953,11 +953,11 @@ mod test {
         spawn(proc() {
             let port2 = port.recv();
             let mut stream = TcpWatcher::connect(local_loop(), addr).unwrap();
-            stream.write([0, 1, 2, 3, 4, 5, 6, 7]);
-            stream.write([0, 1, 2, 3, 4, 5, 6, 7]);
+            stream.write([0, 1, 2, 3, 4, 5, 6, 7]).unwrap();
+            stream.write([0, 1, 2, 3, 4, 5, 6, 7]).unwrap();
             port2.recv();
-            stream.write([0, 1, 2, 3, 4, 5, 6, 7]);
-            stream.write([0, 1, 2, 3, 4, 5, 6, 7]);
+            stream.write([0, 1, 2, 3, 4, 5, 6, 7]).unwrap();
+            stream.write([0, 1, 2, 3, 4, 5, 6, 7]).unwrap();
             port2.recv();
         });
 
@@ -1008,7 +1008,7 @@ mod test {
         while stream.is_err() {
             stream = TcpWatcher::connect(local_loop(), addr);
         }
-        stream.unwrap().write([0, 1, 2, 3, 4, 5, 6, 7]);
+        stream.unwrap().write([0, 1, 2, 3, 4, 5, 6, 7]).unwrap();
     }
 
     #[should_fail] #[test]
@@ -1028,7 +1028,7 @@ mod test {
             let w = TcpListener::bind(local_loop(), addr).unwrap();
             let mut w = w.listen().unwrap();
             chan.send(());
-            w.accept();
+            drop(w.accept().unwrap());
         });
         port.recv();
         let _w = TcpWatcher::connect(local_loop(), addr).unwrap();

src/librustuv/pipe.rs

@@ -306,7 +306,7 @@ mod tests {
             let p = PipeListener::bind(local_loop(), &path2.to_c_str()).unwrap();
             let mut p = p.listen().unwrap();
             chan.send(());
-            p.accept();
+            drop(p.accept().unwrap());
         });
         port.recv();
         let _c = PipeWatcher::connect(local_loop(), &path.to_c_str()).unwrap();

src/librustuv/queue.rs

@@ -67,7 +67,7 @@ extern fn async_cb(handle: *uvll::uv_async_t, status: c_int) {
     loop {
         match state.consumer.pop() {
             mpsc::Data(Task(task)) => {
-                task.wake().map(|t| t.reawaken(true));
+                let _ = task.wake().map(|t| t.reawaken(true));
             }
             mpsc::Data(Increment) => unsafe {
                 if state.refcnt == 0 {

src/librustuv/signal.rs

@@ -86,7 +86,7 @@ mod test {
                                          chan);
 
         spawn(proc() {
-            port.try_recv();
+            let _ = port.recv_opt();
         });
 
         // when we drop the SignalWatcher we're going to destroy the channel,

src/librustuv/timer.rs

@@ -138,11 +138,11 @@ extern fn timer_cb(handle: *uvll::uv_timer_t, status: c_int) {
 
     match timer.action.take_unwrap() {
         WakeTask(task) => {
-            task.wake().map(|t| t.reawaken(true));
+            let _ = task.wake().map(|t| t.reawaken(true));
         }
-        SendOnce(chan) => { chan.try_send(()); }
+        SendOnce(chan) => { let _ = chan.try_send(()); }
         SendMany(chan, id) => {
-            chan.try_send(());
+            let _ = chan.try_send(());
 
             // Note that the above operation could have performed some form of
             // scheduling. This means that the timer may have decided to insert
@@ -246,7 +246,7 @@ mod test {
         let timer_port = timer.period(1000);
 
         spawn(proc() {
-            timer_port.recv_opt();
+            let _ = timer_port.recv_opt();
         });
 
         // when we drop the TimerWatcher we're going to destroy the channel,
@@ -260,10 +260,10 @@ mod test {
         let timer_port = timer.period(1000);
 
         spawn(proc() {
-            timer_port.recv_opt();
+            let _ = timer_port.recv_opt();
         });
 
-        timer.oneshot(1);
+        drop(timer.oneshot(1));
     }
     #[test]
     fn reset_doesnt_switch_tasks2() {
@@ -272,7 +272,7 @@ mod test {
         let timer_port = timer.period(1000);
 
         spawn(proc() {
-            timer_port.recv_opt();
+            let _ = timer_port.recv_opt();
         });
 
         timer.sleep(1);
@@ -299,7 +299,7 @@ mod test {
     #[test]
     fn receiver_goes_away_oneshot() {
         let mut timer1 = TimerWatcher::new(local_loop());
-        timer1.oneshot(1);
+        drop(timer1.oneshot(1));
         let mut timer2 = TimerWatcher::new(local_loop());
         // while sleeping, the prevous timer should fire and not have its
         // callback do something terrible.
@@ -309,7 +309,7 @@ mod test {
     #[test]
     fn receiver_goes_away_period() {
         let mut timer1 = TimerWatcher::new(local_loop());
-        timer1.period(1);
+        drop(timer1.period(1));
         let mut timer2 = TimerWatcher::new(local_loop());
         // while sleeping, the prevous timer should fire and not have its
         // callback do something terrible.

src/librustuv/uvio.rs

@@ -71,7 +71,7 @@ impl Drop for UvEventLoop {
         // after the loop has been closed because during the closing of the loop
         // the handle is required to be used apparently.
         let handle = self.uvio.handle_pool.get_ref().handle();
-        self.uvio.handle_pool.take();
+        drop(self.uvio.handle_pool.take());
         self.uvio.loop_.close();
         unsafe { uvll::free_handle(handle) }
     }

src/libstd/comm/mod.rs

@@ -1252,7 +1252,7 @@ mod test {
             spawn(proc() {
                 let _p = port;
             });
-            task::try(proc() {
+            let _ = task::try(proc() {
                 chan.send(1);
             });
         }

src/libstd/fmt/mod.rs

@@ -163,9 +163,10 @@ method of the signature:
 
 ```rust
 # use std;
+# mod fmt { pub type Result = (); }
 # struct T;
 # trait SomeName<T> {
-fn fmt(value: &T, f: &mut std::fmt::Formatter);
+fn fmt(value: &T, f: &mut std::fmt::Formatter) -> fmt::Result;
 # }
 ```
 
@@ -174,7 +175,14 @@ emit output into the `f.buf` stream. It is up to each format trait
 implementation to correctly adhere to the requested formatting parameters. The
 values of these parameters will be listed in the fields of the `Formatter`
 struct. In order to help with this, the `Formatter` struct also provides some
-helper methods. An example of implementing the formatting traits would look
+helper methods.
+
+Additionally, the return value of this function is `fmt::Result` which is a
+typedef to `Result<(), IoError>` (also known as `IoError<()>`). Formatting
+implementations should ensure that they return errors from `write!` correctly
+(propagating errors upward).
+
+An example of implementing the formatting traits would look
 like:
 
 ```rust
@@ -187,7 +195,7 @@ struct Vector2D {
 }
 
 impl fmt::Show for Vector2D {
-    fn fmt(obj: &Vector2D, f: &mut fmt::Formatter) {
+    fn fmt(obj: &Vector2D, f: &mut fmt::Formatter) -> fmt::Result {
         // The `f.buf` value is of the type `&mut io::Writer`, which is what th
         // write! macro is expecting. Note that this formatting ignores the
         // various flags provided to format strings.
@@ -198,7 +206,7 @@ impl fmt::Show for Vector2D {
 // Different traits allow different forms of output of a type. The meaning of
 // this format is to print the magnitude of a vector.
 impl fmt::Binary for Vector2D {
-    fn fmt(obj: &Vector2D, f: &mut fmt::Formatter) {
+    fn fmt(obj: &Vector2D, f: &mut fmt::Formatter) -> fmt::Result {
         let magnitude = (obj.x * obj.x + obj.y * obj.y) as f64;
         let magnitude = magnitude.sqrt();
 
@@ -207,7 +215,7 @@ impl fmt::Binary for Vector2D {
         // for details, and the function `pad` can be used to pad strings.
         let decimals = f.precision.unwrap_or(3);
         let string = f64::to_str_exact(magnitude, decimals);
-        f.pad_integral(string.as_bytes(), "", true);
+        f.pad_integral(string.as_bytes(), "", true)
     }
 }
 
@@ -242,6 +250,7 @@ strings and instead directly write the output. Under the hood, this function is
 actually invoking the `write` function defined in this module. Example usage is:
 
 ```rust
+# #[allow(unused_must_use)];
 use std::io;
 
 let mut w = io::MemWriter::new();
@@ -468,16 +477,20 @@ will look like `"\\{"`.
 
 */
 
-#[cfg(not(stage0))]
-use prelude::*;
-
 use cast;
 use char::Char;
+use container::Container;
 use io::MemWriter;
 use io;
-use str;
+use iter::{Iterator, range};
+use num::Signed;
+use option::{Option,Some,None};
 use repr;
+use result::{Ok, Err};
+use str::StrSlice;
+use str;
 use util;
+use vec::ImmutableVector;
 use vec;
 
 // NOTE this is just because the `prelude::*` import above includes
@@ -485,22 +498,11 @@ use vec;
 #[cfg(stage0)]
 pub use Default = fmt::Show; // export required for `format!()` etc.
 
-#[cfg(stage0)]
-use container::Container;
-#[cfg(stage0)]
-use iter::{Iterator, range};
-#[cfg(stage0)]
-use option::{Option,Some,None};
-#[cfg(stage0)]
-use vec::ImmutableVector;
-#[cfg(stage0)]
-use str::StrSlice;
-#[cfg(stage0)]
-use num::Signed;
-
 pub mod parse;
 pub mod rt;
 
+pub type Result = io::IoResult<()>;
+
 /// A struct to represent both where to emit formatting strings to and how they
 /// should be formatted. A mutable version of this is passed to all formatting
 /// traits.
@@ -527,7 +529,7 @@ pub struct Formatter<'a> {
 /// compile time it is ensured that the function and the value have the correct
 /// types, and then this struct is used to canonicalize arguments to one type.
 pub struct Argument<'a> {
-    priv formatter: extern "Rust" fn(&util::Void, &mut Formatter),
+    priv formatter: extern "Rust" fn(&util::Void, &mut Formatter) -> Result,
     priv value: &'a util::Void,
 }
 
@@ -561,50 +563,50 @@ pub struct Arguments<'a> {
 /// to this trait. There is not an explicit way of selecting this trait to be
 /// used for formatting, it is only if no other format is specified.
 #[allow(missing_doc)]
-pub trait Show { fn fmt(&Self, &mut Formatter); }
+pub trait Show { fn fmt(&Self, &mut Formatter) -> Result; }
 
 /// Format trait for the `b` character
 #[allow(missing_doc)]
-pub trait Bool { fn fmt(&Self, &mut Formatter); }
+pub trait Bool { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `c` character
 #[allow(missing_doc)]
-pub trait Char { fn fmt(&Self, &mut Formatter); }
+pub trait Char { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `i` and `d` characters
 #[allow(missing_doc)]
-pub trait Signed { fn fmt(&Self, &mut Formatter); }
+pub trait Signed { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `u` character
 #[allow(missing_doc)]
-pub trait Unsigned { fn fmt(&Self, &mut Formatter); }
+pub trait Unsigned { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `o` character
 #[allow(missing_doc)]
-pub trait Octal { fn fmt(&Self, &mut Formatter); }
+pub trait Octal { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `b` character
 #[allow(missing_doc)]
-pub trait Binary { fn fmt(&Self, &mut Formatter); }
+pub trait Binary { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `x` character
 #[allow(missing_doc)]
-pub trait LowerHex { fn fmt(&Self, &mut Formatter); }
+pub trait LowerHex { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `X` character
 #[allow(missing_doc)]
-pub trait UpperHex { fn fmt(&Self, &mut Formatter); }
+pub trait UpperHex { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `s` character
 #[allow(missing_doc)]
-pub trait String { fn fmt(&Self, &mut Formatter); }
+pub trait String { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `?` character
 #[allow(missing_doc)]
-pub trait Poly { fn fmt(&Self, &mut Formatter); }
+pub trait Poly { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `p` character
 #[allow(missing_doc)]
-pub trait Pointer { fn fmt(&Self, &mut Formatter); }
+pub trait Pointer { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `f` character
 #[allow(missing_doc)]
-pub trait Float { fn fmt(&Self, &mut Formatter); }
+pub trait Float { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `e` character
 #[allow(missing_doc)]
-pub trait LowerExp { fn fmt(&Self, &mut Formatter); }
+pub trait LowerExp { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `E` character
 #[allow(missing_doc)]
-pub trait UpperExp { fn fmt(&Self, &mut Formatter); }
+pub trait UpperExp { fn fmt(&Self, &mut Formatter) -> Result; }
 
 // FIXME #11938 - UFCS would make us able call the above methods
 // directly Show::show(x, fmt).
@@ -617,7 +619,7 @@ macro_rules! uniform_fn_call_workaround {
     ($( $name: ident, $trait_: ident; )*) => {
         $(
             #[doc(hidden)]
-            pub fn $name<T: $trait_>(x: &T, fmt: &mut Formatter) {
+            pub fn $name<T: $trait_>(x: &T, fmt: &mut Formatter) -> Result {
                 $trait_::fmt(x, fmt)
             }
             )*
@@ -653,21 +655,22 @@ uniform_fn_call_workaround! {
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::fmt;
 /// use std::io;
 ///
 /// let w = &mut io::stdout() as &mut io::Writer;
-/// format_args!(|args| { fmt::write(w, args) }, "Hello, {}!", "world");
+/// format_args!(|args| { fmt::write(w, args); }, "Hello, {}!", "world");
 /// ```
-pub fn write(output: &mut io::Writer, args: &Arguments) {
+pub fn write(output: &mut io::Writer, args: &Arguments) -> Result {
     unsafe { write_unsafe(output, args.fmt, args.args) }
 }
 
 /// The `writeln` function takes the same arguments as `write`, except that it
 /// will also write a newline (`\n`) character at the end of the format string.
-pub fn writeln(output: &mut io::Writer, args: &Arguments) {
-    unsafe { write_unsafe(output, args.fmt, args.args) }
-    output.write(['\n' as u8]);
+pub fn writeln(output: &mut io::Writer, args: &Arguments) -> Result {
+    let first = unsafe { write_unsafe(output, args.fmt, args.args) };
+    first.and_then(|()| output.write(['\n' as u8]))
 }
 
 /// The `write_unsafe` function takes an output stream, a precompiled format
@@ -692,7 +695,7 @@ pub fn writeln(output: &mut io::Writer, args: &Arguments) {
 /// format string.
 pub unsafe fn write_unsafe(output: &mut io::Writer,
                            fmt: &[rt::Piece],
-                           args: &[Argument]) {
+                           args: &[Argument]) -> Result {
     let mut formatter = Formatter {
         flags: 0,
         width: None,
@@ -704,8 +707,9 @@ pub unsafe fn write_unsafe(output: &mut io::Writer,
         curarg: args.iter(),
     };
     for piece in fmt.iter() {
-        formatter.run(piece, None);
+        if_ok!(formatter.run(piece, None));
     }
+    Ok(())
 }
 
 /// The format function takes a precompiled format string and a list of
@@ -752,7 +756,7 @@ pub fn format(args: &Arguments) -> ~str {
 /// format string.
 pub unsafe fn format_unsafe(fmt: &[rt::Piece], args: &[Argument]) -> ~str {
     let mut output = MemWriter::new();
-    write_unsafe(&mut output as &mut io::Writer, fmt, args);
+    write_unsafe(&mut output as &mut io::Writer, fmt, args).unwrap();
     return str::from_utf8_owned(output.unwrap()).unwrap();
 }
 
@@ -762,10 +766,10 @@ impl<'a> Formatter<'a> {
     // at runtime. This consumes all of the compile-time statics generated by
     // the format! syntax extension.
 
-    fn run(&mut self, piece: &rt::Piece, cur: Option<&str>) {
+    fn run(&mut self, piece: &rt::Piece, cur: Option<&str>) -> Result {
         match *piece {
-            rt::String(s) => { self.buf.write(s.as_bytes()); }
-            rt::CurrentArgument(()) => { self.buf.write(cur.unwrap().as_bytes()); }
+            rt::String(s) => self.buf.write(s.as_bytes()),
+            rt::CurrentArgument(()) => self.buf.write(cur.unwrap().as_bytes()),
             rt::Argument(ref arg) => {
                 // Fill in the format parameters into the formatter
                 self.fill = arg.format.fill;
@@ -782,8 +786,8 @@ impl<'a> Formatter<'a> {
 
                 // Then actually do some printing
                 match arg.method {
-                    None => { (value.formatter)(value.value, self); }
-                    Some(ref method) => { self.execute(*method, value); }
+                    None => (value.formatter)(value.value, self),
+                    Some(ref method) => self.execute(*method, value)
                 }
             }
         }
@@ -804,7 +808,7 @@ impl<'a> Formatter<'a> {
         }
     }
 
-    fn execute(&mut self, method: &rt::Method, arg: Argument) {
+    fn execute(&mut self, method: &rt::Method, arg: Argument) -> Result {
         match *method {
             // Pluralization is selection upon a numeric value specified as the
             // parameter.
@@ -847,7 +851,7 @@ impl<'a> Formatter<'a> {
                     }
                 }
 
-                self.runplural(value, *default);
+                self.runplural(value, *default)
             }
 
             // Select is just a matching against the string specified.
@@ -860,24 +864,26 @@ impl<'a> Formatter<'a> {
                 for s in selectors.iter() {
                     if s.selector == value {
                         for piece in s.result.iter() {
-                            self.run(piece, Some(value));
+                            if_ok!(self.run(piece, Some(value)));
                         }
-                        return;
+                        return Ok(());
                     }
                 }
                 for piece in default.iter() {
-                    self.run(piece, Some(value));
+                    if_ok!(self.run(piece, Some(value)));
                 }
+                Ok(())
             }
         }
     }
 
-    fn runplural(&mut self, value: uint, pieces: &[rt::Piece]) {
+    fn runplural(&mut self, value: uint, pieces: &[rt::Piece]) -> Result {
         ::uint::to_str_bytes(value, 10, |buf| {
             let valuestr = str::from_utf8(buf).unwrap();
             for piece in pieces.iter() {
-                self.run(piece, Some(valuestr));
+                if_ok!(self.run(piece, Some(valuestr)));
             }
+            Ok(())
         })
     }
 
@@ -899,7 +905,7 @@ impl<'a> Formatter<'a> {
     /// This function will correctly account for the flags provided as well as
     /// the minimum width. It will not take precision into account.
     pub fn pad_integral(&mut self, s: &[u8], alternate_prefix: &str,
-                        positive: bool) {
+                        positive: bool) -> Result {
         use fmt::parse::{FlagAlternate, FlagSignPlus, FlagSignAwareZeroPad};
 
         let mut actual_len = s.len();
@@ -916,32 +922,32 @@ impl<'a> Formatter<'a> {
         let sign = |this: &mut Formatter| {
             if !signprinted {
                 if this.flags & 1 << (FlagSignPlus as uint) != 0 && positive {
-                    this.buf.write(['+' as u8]);
+                    if_ok!(this.buf.write(['+' as u8]));
                 } else if !positive {
-                    this.buf.write(['-' as u8]);
+                    if_ok!(this.buf.write(['-' as u8]));
                 }
                 if this.flags & 1 << (FlagAlternate as uint) != 0 {
-                    this.buf.write(alternate_prefix.as_bytes());
+                    if_ok!(this.buf.write(alternate_prefix.as_bytes()));
                 }
                 signprinted = true;
             }
+            Ok(())
         };
 
         let emit = |this: &mut Formatter| {
-            sign(this);
-            this.buf.write(s);
+            sign(this).and_then(|()| this.buf.write(s))
         };
 
         match self.width {
-            None => { emit(self) }
-            Some(min) if actual_len >= min => { emit(self) }
+            None => emit(self),
+            Some(min) if actual_len >= min => emit(self),
             Some(min) => {
                 if self.flags & 1 << (FlagSignAwareZeroPad as uint) != 0 {
                     self.fill = '0';
-                    sign(self);
+                    if_ok!(sign(self));
                 }
                 self.with_padding(min - actual_len, parse::AlignRight, |me| {
-                    emit(me);
+                    emit(me)
                 })
             }
         }
@@ -958,11 +964,10 @@ impl<'a> Formatter<'a> {
     ///               is longer than this length
     ///
     /// Notably this function ignored the `flag` parameters
-    pub fn pad(&mut self, s: &str) {
+    pub fn pad(&mut self, s: &str) -> Result {
         // Make sure there's a fast path up front
         if self.width.is_none() && self.precision.is_none() {
-            self.buf.write(s.as_bytes());
-            return
+            return self.buf.write(s.as_bytes());
         }
         // The `precision` field can be interpreted as a `max-width` for the
         // string being formatted
@@ -974,8 +979,7 @@ impl<'a> Formatter<'a> {
                 let char_len = s.char_len();
                 if char_len >= max {
                     let nchars = ::cmp::min(max, char_len);
-                    self.buf.write(s.slice_chars(0, nchars).as_bytes());
-                    return
+                    return self.buf.write(s.slice_chars(0, nchars).as_bytes());
                 }
             }
             None => {}
@@ -985,7 +989,7 @@ impl<'a> Formatter<'a> {
         match self.width {
             // If we're under the maximum length, and there's no minimum length
             // requirements, then we can just emit the string
-            None => { self.buf.write(s.as_bytes()) }
+            None => self.buf.write(s.as_bytes()),
 
             // If we're under the maximum width, check if we're over the minimum
             // width, if so it's as easy as just emitting the string.
@@ -997,7 +1001,7 @@ impl<'a> Formatter<'a> {
             // up the minimum width with the specified string + some alignment.
             Some(width) => {
                 self.with_padding(width - s.len(), parse::AlignLeft, |me| {
-                    me.buf.write(s.as_bytes());
+                    me.buf.write(s.as_bytes())
                 })
             }
         }
@@ -1006,29 +1010,30 @@ impl<'a> Formatter<'a> {
     fn with_padding(&mut self,
                     padding: uint,
                     default: parse::Alignment,
-                    f: |&mut Formatter|) {
+                    f: |&mut Formatter| -> Result) -> Result {
         let align = match self.align {
             parse::AlignUnknown => default,
             parse::AlignLeft | parse::AlignRight => self.align
         };
         if align == parse::AlignLeft {
-            f(self);
+            if_ok!(f(self));
         }
         let mut fill = [0u8, ..4];
         let len = self.fill.encode_utf8(fill);
         for _ in range(0, padding) {
-            self.buf.write(fill.slice_to(len));
+            if_ok!(self.buf.write(fill.slice_to(len)));
         }
         if align == parse::AlignRight {
-            f(self);
+            if_ok!(f(self));
         }
+        Ok(())
     }
 }
 
 /// This is a function which calls are emitted to by the compiler itself to
 /// create the Argument structures that are passed into the `format` function.
 #[doc(hidden)] #[inline]
-pub fn argument<'a, T>(f: extern "Rust" fn(&T, &mut Formatter),
+pub fn argument<'a, T>(f: extern "Rust" fn(&T, &mut Formatter) -> Result,
                        t: &'a T) -> Argument<'a> {
     unsafe {
         Argument {
@@ -1055,41 +1060,41 @@ pub fn argumentuint<'a>(s: &'a uint) -> Argument<'a> {
 // Implementations of the core formatting traits
 
 impl Bool for bool {
-    fn fmt(b: &bool, f: &mut Formatter) {
-        String::fmt(&(if *b {"true"} else {"false"}), f);
+    fn fmt(b: &bool, f: &mut Formatter) -> Result {
+        String::fmt(&(if *b {"true"} else {"false"}), f)
     }
 }
 
 impl<'a, T: str::Str> String for T {
-    fn fmt(s: &T, f: &mut Formatter) {
-        f.pad(s.as_slice());
+    fn fmt(s: &T, f: &mut Formatter) -> Result {
+        f.pad(s.as_slice())
     }
 }
 
 impl Char for char {
-    fn fmt(c: &char, f: &mut Formatter) {
+    fn fmt(c: &char, f: &mut Formatter) -> Result {
         let mut utf8 = [0u8, ..4];
         let amt = c.encode_utf8(utf8);
         let s: &str = unsafe { cast::transmute(utf8.slice_to(amt)) };
-        String::fmt(&s, f);
+        String::fmt(&s, f)
     }
 }
 
 macro_rules! int_base(($ty:ident, $into:ident, $base:expr,
                        $name:ident, $prefix:expr) => {
     impl $name for $ty {
-        fn fmt(c: &$ty, f: &mut Formatter) {
+        fn fmt(c: &$ty, f: &mut Formatter) -> Result {
             ::$into::to_str_bytes(*c as $into, $base, |buf| {
-                f.pad_integral(buf, $prefix, true);
+                f.pad_integral(buf, $prefix, true)
             })
         }
     }
 })
 macro_rules! upper_hex(($ty:ident, $into:ident) => {
     impl UpperHex for $ty {
-        fn fmt(c: &$ty, f: &mut Formatter) {
+        fn fmt(c: &$ty, f: &mut Formatter) -> Result {
             ::$into::to_str_bytes(*c as $into, 16, |buf| {
-                upperhex(buf, f);
+                upperhex(buf, f)
             })
         }
     }
@@ -1097,7 +1102,7 @@ macro_rules! upper_hex(($ty:ident, $into:ident) => {
 // Not sure why, but this causes an "unresolved enum variant, struct or const"
 // when inlined into the above macro...
 #[doc(hidden)]
-pub fn upperhex(buf: &[u8], f: &mut Formatter) {
+pub fn upperhex(buf: &[u8], f: &mut Formatter) -> Result {
     let mut local = [0u8, ..16];
     for i in ::iter::range(0, buf.len()) {
         local[i] = match buf[i] as char {
@@ -1105,16 +1110,16 @@ pub fn upperhex(buf: &[u8], f: &mut Formatter) {
             c => c as u8,
         }
     }
-    f.pad_integral(local.slice_to(buf.len()), "0x", true);
+    f.pad_integral(local.slice_to(buf.len()), "0x", true)
 }
 
 macro_rules! integer(($signed:ident, $unsigned:ident) => {
     // Signed is special because it actuall emits the negative sign,
     // nothing else should do that, however.
     impl Signed for $signed {
-        fn fmt(c: &$signed, f: &mut Formatter) {
+        fn fmt(c: &$signed, f: &mut Formatter) -> Result {
             ::$unsigned::to_str_bytes(c.abs() as $unsigned, 10, |buf| {
-                f.pad_integral(buf, "", *c >= 0);
+                f.pad_integral(buf, "", *c >= 0)
             })
         }
     }
@@ -1138,35 +1143,35 @@ integer!(i64, u64)
 
 macro_rules! floating(($ty:ident) => {
     impl Float for $ty {
-        fn fmt(f: &$ty, fmt: &mut Formatter) {
+        fn fmt(f: &$ty, fmt: &mut Formatter) -> Result {
             // FIXME: this shouldn't perform an allocation
             let s = match fmt.precision {
                 Some(i) => ::$ty::to_str_exact(f.abs(), i),
                 None => ::$ty::to_str_digits(f.abs(), 6)
             };
-            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0);
+            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0)
         }
     }
 
     impl LowerExp for $ty {
-        fn fmt(f: &$ty, fmt: &mut Formatter) {
+        fn fmt(f: &$ty, fmt: &mut Formatter) -> Result {
             // FIXME: this shouldn't perform an allocation
             let s = match fmt.precision {
                 Some(i) => ::$ty::to_str_exp_exact(f.abs(), i, false),
                 None => ::$ty::to_str_exp_digits(f.abs(), 6, false)
             };
-            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0);
+            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0)
         }
     }
 
     impl UpperExp for $ty {
-        fn fmt(f: &$ty, fmt: &mut Formatter) {
+        fn fmt(f: &$ty, fmt: &mut Formatter) -> Result {
             // FIXME: this shouldn't perform an allocation
             let s = match fmt.precision {
                 Some(i) => ::$ty::to_str_exp_exact(f.abs(), i, true),
                 None => ::$ty::to_str_exp_digits(f.abs(), 6, true)
             };
-            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0);
+            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0)
         }
     }
 })
@@ -1174,39 +1179,41 @@ floating!(f32)
 floating!(f64)
 
 impl<T> Poly for T {
-    fn fmt(t: &T, f: &mut Formatter) {
+    fn fmt(t: &T, f: &mut Formatter) -> Result {
         match (f.width, f.precision) {
             (None, None) => {
-                repr::write_repr(f.buf, t);
+                repr::write_repr(f.buf, t)
             }
 
             // If we have a specified width for formatting, then we have to make
             // this allocation of a new string
             _ => {
                 let s = repr::repr_to_str(t);
-                f.pad(s);
+                f.pad(s)
             }
         }
     }
 }
 
 impl<T> Pointer for *T {
-    fn fmt(t: &*T, f: &mut Formatter) {
+    fn fmt(t: &*T, f: &mut Formatter) -> Result {
         f.flags |= 1 << (parse::FlagAlternate as uint);
         ::uint::to_str_bytes(*t as uint, 16, |buf| {
-            f.pad_integral(buf, "0x", true);
+            f.pad_integral(buf, "0x", true)
         })
     }
 }
 impl<T> Pointer for *mut T {
-    fn fmt(t: &*mut T, f: &mut Formatter) { Pointer::fmt(&(*t as *T), f) }
+    fn fmt(t: &*mut T, f: &mut Formatter) -> Result {
+        Pointer::fmt(&(*t as *T), f)
+    }
 }
 
 // Implementation of Show for various core types
 
 macro_rules! delegate(($ty:ty to $other:ident) => {
     impl<'a> Show for $ty {
-        fn fmt(me: &$ty, f: &mut Formatter) {
+        fn fmt(me: &$ty, f: &mut Formatter) -> Result {
             $other::fmt(me, f)
         }
     }
@@ -1229,10 +1236,10 @@ delegate!(f32 to Float)
 delegate!(f64 to Float)
 
 impl<T> Show for *T {
-    fn fmt(me: &*T, f: &mut Formatter) { Pointer::fmt(me, f) }
+    fn fmt(me: &*T, f: &mut Formatter) -> Result { Pointer::fmt(me, f) }
 }
 impl<T> Show for *mut T {
-    fn fmt(me: &*mut T, f: &mut Formatter) { Pointer::fmt(me, f) }
+    fn fmt(me: &*mut T, f: &mut Formatter) -> Result { Pointer::fmt(me, f) }
 }
 
 // If you expected tests to be here, look instead at the run-pass/ifmt.rs test,

src/libstd/hash.rs

@@ -27,13 +27,14 @@
 #[allow(missing_doc)];
 
 use container::Container;
+use io::{Writer, IoResult};
 use iter::Iterator;
+use num::ToStrRadix;
 use option::{Some, None};
-use io::Writer;
+use result::Ok;
 use str::OwnedStr;
 use to_bytes::IterBytes;
 use vec::ImmutableVector;
-use num::ToStrRadix;
 
 // Alias `SipState` to `State`.
 pub use State = hash::SipState;
@@ -164,7 +165,7 @@ macro_rules! compress (
 impl Writer for SipState {
     // Methods for io::writer
     #[inline]
-    fn write(&mut self, msg: &[u8]) {
+    fn write(&mut self, msg: &[u8]) -> IoResult<()> {
         let length = msg.len();
         self.length += length;
 
@@ -180,7 +181,7 @@ impl Writer for SipState {
                     t += 1;
                 }
                 self.ntail += length;
-                return;
+                return Ok(())
             }
 
             let mut t = 0;
@@ -222,17 +223,14 @@ impl Writer for SipState {
             t += 1
         }
         self.ntail = left;
-    }
-
-    fn flush(&mut self) {
-        // No-op
+        Ok(())
     }
 }
 
 impl Streaming for SipState {
     #[inline]
     fn input(&mut self, buf: &[u8]) {
-        self.write(buf);
+        self.write(buf).unwrap();
     }
 
     #[inline]

src/libstd/io/buffered.rs

@@ -11,10 +11,11 @@
 //! Buffering wrappers for I/O traits
 
 use container::Container;
-use io::{Reader, Writer, Stream, Buffer, DEFAULT_BUF_SIZE};
+use io::{Reader, Writer, Stream, Buffer, DEFAULT_BUF_SIZE, IoResult};
 use iter::ExactSize;
 use num;
-use option::{Option, Some, None};
+use option::{Some, None};
+use result::{Ok, Err};
 use vec::{OwnedVector, ImmutableVector, MutableVector};
 use vec;
 
@@ -30,14 +31,13 @@ use vec;
 /// ```rust
 /// use std::io::{BufferedReader, File};
 ///
-/// # let _g = ::std::io::ignore_io_error();
 /// let file = File::open(&Path::new("message.txt"));
 /// let mut reader = BufferedReader::new(file);
 ///
 /// let mut buf = [0, ..100];
 /// match reader.read(buf) {
-///     Some(nread) => println!("Read {} bytes", nread),
-///     None => println!("At the end of the file!")
+///     Ok(nread) => println!("Read {} bytes", nread),
+///     Err(e) => println!("error reading: {}", e)
 /// }
 /// ```
 pub struct BufferedReader<R> {
@@ -86,17 +86,12 @@ impl<R: Reader> BufferedReader<R> {
 }
 
 impl<R: Reader> Buffer for BufferedReader<R> {
-    fn fill<'a>(&'a mut self) -> &'a [u8] {
+    fn fill<'a>(&'a mut self) -> IoResult<&'a [u8]> {
         if self.pos == self.cap {
-            match self.inner.read(self.buf) {
-                Some(cap) => {
-                    self.pos = 0;
-                    self.cap = cap;
-                }
-                None => { self.eof = true; }
-            }
+            self.cap = if_ok!(self.inner.read(self.buf));
+            self.pos = 0;
         }
-        return self.buf.slice(self.pos, self.cap);
+        Ok(self.buf.slice(self.pos, self.cap))
     }
 
     fn consume(&mut self, amt: uint) {
@@ -106,18 +101,15 @@ impl<R: Reader> Buffer for BufferedReader<R> {
 }
 
 impl<R: Reader> Reader for BufferedReader<R> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
         let nread = {
-            let available = self.fill();
+            let available = if_ok!(self.fill());
             let nread = num::min(available.len(), buf.len());
             vec::bytes::copy_memory(buf, available.slice_to(nread));
             nread
         };
         self.pos += nread;
-        if nread == 0 && buf.len() != 0 && self.eof {
-            return None;
-        }
-        Some(nread)
+        Ok(nread)
     }
 }
 
@@ -128,9 +120,9 @@ impl<R: Reader> Reader for BufferedReader<R> {
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::{BufferedWriter, File};
 ///
-/// # let _g = ::std::io::ignore_io_error();
 /// let file = File::open(&Path::new("message.txt"));
 /// let mut writer = BufferedWriter::new(file);
 ///
@@ -161,10 +153,13 @@ impl<W: Writer> BufferedWriter<W> {
         BufferedWriter::with_capacity(DEFAULT_BUF_SIZE, inner)
     }
 
-    fn flush_buf(&mut self) {
+    fn flush_buf(&mut self) -> IoResult<()> {
         if self.pos != 0 {
-            self.inner.write(self.buf.slice_to(self.pos));
+            let ret = self.inner.write(self.buf.slice_to(self.pos));
             self.pos = 0;
+            ret
+        } else {
+            Ok(())
         }
     }
 
@@ -178,29 +173,30 @@ impl<W: Writer> BufferedWriter<W> {
     ///
     /// The buffer is flushed before returning the writer.
     pub fn unwrap(mut self) -> W {
-        self.flush_buf();
+        // FIXME: is failing the right thing to do if flushing fails?
+        self.flush_buf().unwrap();
         self.inner
     }
 }
 
 impl<W: Writer> Writer for BufferedWriter<W> {
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
         if self.pos + buf.len() > self.buf.len() {
-            self.flush_buf();
+            if_ok!(self.flush_buf());
         }
 
         if buf.len() > self.buf.len() {
-            self.inner.write(buf);
+            self.inner.write(buf)
         } else {
             let dst = self.buf.mut_slice_from(self.pos);
             vec::bytes::copy_memory(dst, buf);
             self.pos += buf.len();
+            Ok(())
         }
     }
 
-    fn flush(&mut self) {
-        self.flush_buf();
-        self.inner.flush();
+    fn flush(&mut self) -> IoResult<()> {
+        self.flush_buf().and_then(|()| self.inner.flush())
     }
 }
 
@@ -234,18 +230,19 @@ impl<W: Writer> LineBufferedWriter<W> {
 }
 
 impl<W: Writer> Writer for LineBufferedWriter<W> {
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
         match buf.iter().rposition(|&b| b == '\n' as u8) {
             Some(i) => {
-                self.inner.write(buf.slice_to(i + 1));
-                self.inner.flush();
-                self.inner.write(buf.slice_from(i + 1));
+                if_ok!(self.inner.write(buf.slice_to(i + 1)));
+                if_ok!(self.inner.flush());
+                if_ok!(self.inner.write(buf.slice_from(i + 1)));
+                Ok(())
             }
             None => self.inner.write(buf),
         }
     }
 
-    fn flush(&mut self) { self.inner.flush() }
+    fn flush(&mut self) -> IoResult<()> { self.inner.flush() }
 }
 
 struct InternalBufferedWriter<W>(BufferedWriter<W>);
@@ -258,7 +255,9 @@ impl<W> InternalBufferedWriter<W> {
 }
 
 impl<W: Reader> Reader for InternalBufferedWriter<W> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.get_mut_ref().inner.read(buf) }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
+        self.get_mut_ref().inner.read(buf)
+    }
 }
 
 /// Wraps a Stream and buffers input and output to and from it
@@ -268,9 +267,9 @@ impl<W: Reader> Reader for InternalBufferedWriter<W> {
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::{BufferedStream, File};
 ///
-/// # let _g = ::std::io::ignore_io_error();
 /// let file = File::open(&Path::new("message.txt"));
 /// let mut stream = BufferedStream::new(file);
 ///
@@ -279,8 +278,8 @@ impl<W: Reader> Reader for InternalBufferedWriter<W> {
 ///
 /// let mut buf = [0, ..100];
 /// match stream.read(buf) {
-///     Some(nread) => println!("Read {} bytes", nread),
-///     None => println!("At the end of the stream!")
+///     Ok(nread) => println!("Read {} bytes", nread),
+///     Err(e) => println!("error reading: {}", e)
 /// }
 /// ```
 pub struct BufferedStream<S> {
@@ -326,17 +325,23 @@ impl<S: Stream> BufferedStream<S> {
 }
 
 impl<S: Stream> Buffer for BufferedStream<S> {
-    fn fill<'a>(&'a mut self) -> &'a [u8] { self.inner.fill() }
+    fn fill<'a>(&'a mut self) -> IoResult<&'a [u8]> { self.inner.fill() }
     fn consume(&mut self, amt: uint) { self.inner.consume(amt) }
 }
 
 impl<S: Stream> Reader for BufferedStream<S> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.inner.read(buf) }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
+        self.inner.read(buf)
+    }
 }
 
 impl<S: Stream> Writer for BufferedStream<S> {
-    fn write(&mut self, buf: &[u8]) { self.inner.inner.get_mut_ref().write(buf) }
-    fn flush(&mut self) { self.inner.inner.get_mut_ref().flush() }
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
+        self.inner.inner.get_mut_ref().write(buf)
+    }
+    fn flush(&mut self) -> IoResult<()> {
+        self.inner.inner.get_mut_ref().flush()
+    }
 }
 
 #[cfg(test)]
@@ -354,13 +359,13 @@ mod test {
     pub struct NullStream;
 
     impl Reader for NullStream {
-        fn read(&mut self, _: &mut [u8]) -> Option<uint> {
-            None
+        fn read(&mut self, _: &mut [u8]) -> io::IoResult<uint> {
+            Err(io::standard_error(io::EndOfFile))
         }
     }
 
     impl Writer for NullStream {
-        fn write(&mut self, _: &[u8]) { }
+        fn write(&mut self, _: &[u8]) -> io::IoResult<()> { Ok(()) }
     }
 
     /// A dummy reader intended at testing short-reads propagation.
@@ -369,8 +374,11 @@ mod test {
     }
 
     impl Reader for ShortReader {
-        fn read(&mut self, _: &mut [u8]) -> Option<uint> {
-            self.lengths.shift()
+        fn read(&mut self, _: &mut [u8]) -> io::IoResult<uint> {
+            match self.lengths.shift() {
+                Some(i) => Ok(i),
+                None => Err(io::standard_error(io::EndOfFile))
+            }
         }
     }
 
@@ -381,24 +389,24 @@ mod test {
 
         let mut buf = [0, 0, 0];
         let nread = reader.read(buf);
-        assert_eq!(Some(2), nread);
+        assert_eq!(Ok(2), nread);
         assert_eq!([0, 1, 0], buf);
 
         let mut buf = [0];
         let nread = reader.read(buf);
-        assert_eq!(Some(1), nread);
+        assert_eq!(Ok(1), nread);
         assert_eq!([2], buf);
 
         let mut buf = [0, 0, 0];
         let nread = reader.read(buf);
-        assert_eq!(Some(1), nread);
+        assert_eq!(Ok(1), nread);
         assert_eq!([3, 0, 0], buf);
 
         let nread = reader.read(buf);
-        assert_eq!(Some(1), nread);
+        assert_eq!(Ok(1), nread);
         assert_eq!([4, 0, 0], buf);
 
-        assert_eq!(None, reader.read(buf));
+        assert!(reader.read(buf).is_err());
     }
 
     #[test]
@@ -406,35 +414,35 @@ mod test {
         let inner = MemWriter::new();
         let mut writer = BufferedWriter::with_capacity(2, inner);
 
-        writer.write([0, 1]);
+        writer.write([0, 1]).unwrap();
         assert_eq!([], writer.get_ref().get_ref());
 
-        writer.write([2]);
+        writer.write([2]).unwrap();
         assert_eq!([0, 1], writer.get_ref().get_ref());
 
-        writer.write([3]);
+        writer.write([3]).unwrap();
         assert_eq!([0, 1], writer.get_ref().get_ref());
 
-        writer.flush();
+        writer.flush().unwrap();
         assert_eq!([0, 1, 2, 3], writer.get_ref().get_ref());
 
-        writer.write([4]);
-        writer.write([5]);
+        writer.write([4]).unwrap();
+        writer.write([5]).unwrap();
         assert_eq!([0, 1, 2, 3], writer.get_ref().get_ref());
 
-        writer.write([6]);
+        writer.write([6]).unwrap();
         assert_eq!([0, 1, 2, 3, 4, 5],
                    writer.get_ref().get_ref());
 
-        writer.write([7, 8]);
+        writer.write([7, 8]).unwrap();
         assert_eq!([0, 1, 2, 3, 4, 5, 6],
                    writer.get_ref().get_ref());
 
-        writer.write([9, 10, 11]);
+        writer.write([9, 10, 11]).unwrap();
         assert_eq!([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
                    writer.get_ref().get_ref());
 
-        writer.flush();
+        writer.flush().unwrap();
         assert_eq!([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
                    writer.get_ref().get_ref());
     }
@@ -442,7 +450,7 @@ mod test {
     #[test]
     fn test_buffered_writer_inner_flushes() {
         let mut w = BufferedWriter::with_capacity(3, MemWriter::new());
-        w.write([0, 1]);
+        w.write([0, 1]).unwrap();
         assert_eq!([], w.get_ref().get_ref());
         let w = w.unwrap();
         assert_eq!([0, 1], w.get_ref());
@@ -455,47 +463,49 @@ mod test {
         struct S;
 
         impl io::Writer for S {
-            fn write(&mut self, _: &[u8]) {}
+            fn write(&mut self, _: &[u8]) -> io::IoResult<()> { Ok(()) }
         }
 
         impl io::Reader for S {
-            fn read(&mut self, _: &mut [u8]) -> Option<uint> { None }
+            fn read(&mut self, _: &mut [u8]) -> io::IoResult<uint> {
+                Err(io::standard_error(io::EndOfFile))
+            }
         }
 
         let mut stream = BufferedStream::new(S);
         let mut buf = [];
-        stream.read(buf);
-        stream.write(buf);
-        stream.flush();
+        assert!(stream.read(buf).is_err());
+        stream.write(buf).unwrap();
+        stream.flush().unwrap();
     }
 
     #[test]
     fn test_read_until() {
         let inner = MemReader::new(~[0, 1, 2, 1, 0]);
         let mut reader = BufferedReader::with_capacity(2, inner);
-        assert_eq!(reader.read_until(0), Some(~[0]));
-        assert_eq!(reader.read_until(2), Some(~[1, 2]));
-        assert_eq!(reader.read_until(1), Some(~[1]));
-        assert_eq!(reader.read_until(8), Some(~[0]));
-        assert_eq!(reader.read_until(9), None);
+        assert_eq!(reader.read_until(0), Ok(~[0]));
+        assert_eq!(reader.read_until(2), Ok(~[1, 2]));
+        assert_eq!(reader.read_until(1), Ok(~[1]));
+        assert_eq!(reader.read_until(8), Ok(~[0]));
+        assert!(reader.read_until(9).is_err());
     }
 
     #[test]
     fn test_line_buffer() {
         let mut writer = LineBufferedWriter::new(MemWriter::new());
-        writer.write([0]);
+        writer.write([0]).unwrap();
         assert_eq!(writer.get_ref().get_ref(), []);
-        writer.write([1]);
+        writer.write([1]).unwrap();
         assert_eq!(writer.get_ref().get_ref(), []);
-        writer.flush();
+        writer.flush().unwrap();
         assert_eq!(writer.get_ref().get_ref(), [0, 1]);
-        writer.write([0, '\n' as u8, 1, '\n' as u8, 2]);
+        writer.write([0, '\n' as u8, 1, '\n' as u8, 2]).unwrap();
         assert_eq!(writer.get_ref().get_ref(),
             [0, 1, 0, '\n' as u8, 1, '\n' as u8]);
-        writer.flush();
+        writer.flush().unwrap();
         assert_eq!(writer.get_ref().get_ref(),
             [0, 1, 0, '\n' as u8, 1, '\n' as u8, 2]);
-        writer.write([3, '\n' as u8]);
+        writer.write([3, '\n' as u8]).unwrap();
         assert_eq!(writer.get_ref().get_ref(),
             [0, 1, 0, '\n' as u8, 1, '\n' as u8, 2, 3, '\n' as u8]);
     }
@@ -504,10 +514,10 @@ mod test {
     fn test_read_line() {
         let in_buf = MemReader::new(bytes!("a\nb\nc").to_owned());
         let mut reader = BufferedReader::with_capacity(2, in_buf);
-        assert_eq!(reader.read_line(), Some(~"a\n"));
-        assert_eq!(reader.read_line(), Some(~"b\n"));
-        assert_eq!(reader.read_line(), Some(~"c"));
-        assert_eq!(reader.read_line(), None);
+        assert_eq!(reader.read_line(), Ok(~"a\n"));
+        assert_eq!(reader.read_line(), Ok(~"b\n"));
+        assert_eq!(reader.read_line(), Ok(~"c"));
+        assert!(reader.read_line().is_err());
     }
 
     #[test]
@@ -526,20 +536,20 @@ mod test {
         let inner = ShortReader{lengths: ~[0, 1, 2, 0, 1, 0]};
         let mut reader = BufferedReader::new(inner);
         let mut buf = [0, 0];
-        assert_eq!(reader.read(buf), Some(0));
-        assert_eq!(reader.read(buf), Some(1));
-        assert_eq!(reader.read(buf), Some(2));
-        assert_eq!(reader.read(buf), Some(0));
-        assert_eq!(reader.read(buf), Some(1));
-        assert_eq!(reader.read(buf), Some(0));
-        assert_eq!(reader.read(buf), None);
+        assert_eq!(reader.read(buf), Ok(0));
+        assert_eq!(reader.read(buf), Ok(1));
+        assert_eq!(reader.read(buf), Ok(2));
+        assert_eq!(reader.read(buf), Ok(0));
+        assert_eq!(reader.read(buf), Ok(1));
+        assert_eq!(reader.read(buf), Ok(0));
+        assert!(reader.read(buf).is_err());
     }
 
     #[test]
     fn read_char_buffered() {
         let buf = [195u8, 159u8];
         let mut reader = BufferedReader::with_capacity(1, BufReader::new(buf));
-        assert_eq!(reader.read_char(), Some('ß'));
+        assert_eq!(reader.read_char(), Ok('ß'));
     }
 
     #[bench]

src/libstd/io/comm_adapters.rs

@@ -14,7 +14,7 @@ use comm::{Port, Chan};
 use cmp;
 use io;
 use option::{None, Option, Some};
-use super::{Reader, Writer};
+use super::{Reader, Writer, IoResult};
 use vec::{bytes, CloneableVector, MutableVector, ImmutableVector};
 
 /// Allows reading from a port.
@@ -49,7 +49,7 @@ impl PortReader {
 }
 
 impl Reader for PortReader {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
         let mut num_read = 0;
         loop {
             match self.buf {
@@ -71,10 +71,9 @@ impl Reader for PortReader {
             self.closed = self.buf.is_none();
         }
         if self.closed && num_read == 0 {
-            io::io_error::cond.raise(io::standard_error(io::EndOfFile));
-            None
+            Err(io::standard_error(io::EndOfFile))
         } else {
-            Some(num_read)
+            Ok(num_read)
         }
     }
 }
@@ -98,13 +97,15 @@ impl ChanWriter {
 }
 
 impl Writer for ChanWriter {
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
         if !self.chan.try_send(buf.to_owned()) {
-            io::io_error::cond.raise(io::IoError {
+            Err(io::IoError {
                 kind: io::BrokenPipe,
                 desc: "Pipe closed",
                 detail: None
-            });
+            })
+        } else {
+            Ok(())
         }
     }
 }
@@ -132,36 +133,28 @@ mod test {
         let mut buf = ~[0u8, ..3];
 
 
-        assert_eq!(Some(0), reader.read([]));
+        assert_eq!(Ok(0), reader.read([]));
 
-        assert_eq!(Some(3), reader.read(buf));
+        assert_eq!(Ok(3), reader.read(buf));
         assert_eq!(~[1,2,3], buf);
 
-        assert_eq!(Some(3), reader.read(buf));
+        assert_eq!(Ok(3), reader.read(buf));
         assert_eq!(~[4,5,6], buf);
 
-        assert_eq!(Some(2), reader.read(buf));
+        assert_eq!(Ok(2), reader.read(buf));
         assert_eq!(~[7,8,6], buf);
 
-        let mut err = None;
-        let result = io::io_error::cond.trap(|io::standard_error(k, _, _)| {
-            err = Some(k)
-        }).inside(|| {
-            reader.read(buf)
-        });
-        assert_eq!(Some(io::EndOfFile), err);
-        assert_eq!(None, result);
+        match reader.read(buf) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::EndOfFile),
+        }
         assert_eq!(~[7,8,6], buf);
 
         // Ensure it continues to fail in the same way.
-        err = None;
-        let result = io::io_error::cond.trap(|io::standard_error(k, _, _)| {
-            err = Some(k)
-        }).inside(|| {
-            reader.read(buf)
-        });
-        assert_eq!(Some(io::EndOfFile), err);
-        assert_eq!(None, result);
+        match reader.read(buf) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::EndOfFile),
+        }
         assert_eq!(~[7,8,6], buf);
     }
 
@@ -169,18 +162,15 @@ mod test {
     fn test_chan_writer() {
         let (port, chan) = Chan::new();
         let mut writer = ChanWriter::new(chan);
-        writer.write_be_u32(42);
+        writer.write_be_u32(42).unwrap();
 
         let wanted = ~[0u8, 0u8, 0u8, 42u8];
         let got = task::try(proc() { port.recv() }).unwrap();
         assert_eq!(wanted, got);
 
-        let mut err = None;
-        io::io_error::cond.trap(|io::IoError { kind, .. } | {
-            err = Some(kind)
-        }).inside(|| {
-            writer.write_u8(1)
-        });
-        assert_eq!(Some(io::BrokenPipe), err);
+        match writer.write_u8(1) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::BrokenPipe),
+        }
     }
 }

src/libstd/io/extensions.rs

@@ -46,7 +46,7 @@ impl<'r, R: Reader> Bytes<'r, R> {
 impl<'r, R: Reader> Iterator<u8> for Bytes<'r, R> {
     #[inline]
     fn next(&mut self) -> Option<u8> {
-        self.reader.read_byte()
+        self.reader.read_byte().ok()
     }
 }
 
@@ -125,23 +125,22 @@ pub fn u64_from_be_bytes(data: &[u8],
 
 #[cfg(test)]
 mod test {
-    use unstable::finally::Finally;
     use prelude::*;
+    use io;
     use io::{MemReader, MemWriter};
-    use io::{io_error, placeholder_error};
 
     struct InitialZeroByteReader {
         count: int,
     }
 
     impl Reader for InitialZeroByteReader {
-        fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
             if self.count == 0 {
                 self.count = 1;
-                Some(0)
+                Ok(0)
             } else {
                 buf[0] = 10;
-                Some(1)
+                Ok(1)
             }
         }
     }
@@ -149,17 +148,16 @@ mod test {
     struct EofReader;
 
     impl Reader for EofReader {
-        fn read(&mut self, _: &mut [u8]) -> Option<uint> {
-            None
+        fn read(&mut self, _: &mut [u8]) -> io::IoResult<uint> {
+            Err(io::standard_error(io::EndOfFile))
         }
     }
 
     struct ErroringReader;
 
     impl Reader for ErroringReader {
-        fn read(&mut self, _: &mut [u8]) -> Option<uint> {
-            io_error::cond.raise(placeholder_error());
-            None
+        fn read(&mut self, _: &mut [u8]) -> io::IoResult<uint> {
+            Err(io::standard_error(io::InvalidInput))
         }
     }
 
@@ -168,16 +166,16 @@ mod test {
     }
 
     impl Reader for PartialReader {
-        fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
             if self.count == 0 {
                 self.count = 1;
                 buf[0] = 10;
                 buf[1] = 11;
-                Some(2)
+                Ok(2)
             } else {
                 buf[0] = 12;
                 buf[1] = 13;
-                Some(2)
+                Ok(2)
             }
         }
     }
@@ -187,14 +185,13 @@ mod test {
     }
 
     impl Reader for ErroringLaterReader {
-        fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
             if self.count == 0 {
                 self.count = 1;
                 buf[0] = 10;
-                Some(1)
+                Ok(1)
             } else {
-                io_error::cond.raise(placeholder_error());
-                None
+                Err(io::standard_error(io::InvalidInput))
             }
         }
     }
@@ -204,19 +201,19 @@ mod test {
     }
 
     impl Reader for ThreeChunkReader {
-        fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
             if self.count == 0 {
                 self.count = 1;
                 buf[0] = 10;
                 buf[1] = 11;
-                Some(2)
+                Ok(2)
             } else if self.count == 1 {
                 self.count = 2;
                 buf[0] = 12;
                 buf[1] = 13;
-                Some(2)
+                Ok(2)
             } else {
-                None
+                Err(io::standard_error(io::EndOfFile))
             }
         }
     }
@@ -225,7 +222,7 @@ mod test {
     fn read_byte() {
         let mut reader = MemReader::new(~[10]);
         let byte = reader.read_byte();
-        assert!(byte == Some(10));
+        assert!(byte == Ok(10));
     }
 
     #[test]
@@ -234,24 +231,21 @@ mod test {
             count: 0,
         };
         let byte = reader.read_byte();
-        assert!(byte == Some(10));
+        assert!(byte == Ok(10));
     }
 
     #[test]
     fn read_byte_eof() {
         let mut reader = EofReader;
         let byte = reader.read_byte();
-        assert!(byte == None);
+        assert!(byte.is_err());
     }
 
     #[test]
     fn read_byte_error() {
         let mut reader = ErroringReader;
-        io_error::cond.trap(|_| {
-        }).inside(|| {
-            let byte = reader.read_byte();
-            assert!(byte == None);
-        });
+        let byte = reader.read_byte();
+        assert!(byte.is_err());
     }
 
     #[test]
@@ -267,23 +261,21 @@ mod test {
     fn bytes_eof() {
         let mut reader = EofReader;
         let byte = reader.bytes().next();
-        assert!(byte == None);
+        assert!(byte.is_none());
     }
 
     #[test]
     fn bytes_error() {
         let mut reader = ErroringReader;
         let mut it = reader.bytes();
-        io_error::cond.trap(|_| ()).inside(|| {
-            let byte = it.next();
-            assert!(byte == None);
-        })
+        let byte = it.next();
+        assert!(byte.is_none());
     }
 
     #[test]
     fn read_bytes() {
         let mut reader = MemReader::new(~[10, 11, 12, 13]);
-        let bytes = reader.read_bytes(4);
+        let bytes = reader.read_bytes(4).unwrap();
         assert!(bytes == ~[10, 11, 12, 13]);
     }
 
@@ -292,24 +284,21 @@ mod test {
         let mut reader = PartialReader {
             count: 0,
         };
-        let bytes = reader.read_bytes(4);
+        let bytes = reader.read_bytes(4).unwrap();
         assert!(bytes == ~[10, 11, 12, 13]);
     }
 
     #[test]
     fn read_bytes_eof() {
         let mut reader = MemReader::new(~[10, 11]);
-        io_error::cond.trap(|_| {
-        }).inside(|| {
-            assert!(reader.read_bytes(4) == ~[10, 11]);
-        })
+        assert!(reader.read_bytes(4).is_err());
     }
 
     #[test]
     fn push_bytes() {
         let mut reader = MemReader::new(~[10, 11, 12, 13]);
         let mut buf = ~[8, 9];
-        reader.push_bytes(&mut buf, 4);
+        reader.push_bytes(&mut buf, 4).unwrap();
         assert!(buf == ~[8, 9, 10, 11, 12, 13]);
     }
 
@@ -319,7 +308,7 @@ mod test {
             count: 0,
         };
         let mut buf = ~[8, 9];
-        reader.push_bytes(&mut buf, 4);
+        reader.push_bytes(&mut buf, 4).unwrap();
         assert!(buf == ~[8, 9, 10, 11, 12, 13]);
     }
 
@@ -327,11 +316,8 @@ mod test {
     fn push_bytes_eof() {
         let mut reader = MemReader::new(~[10, 11]);
         let mut buf = ~[8, 9];
-        io_error::cond.trap(|_| {
-        }).inside(|| {
-            reader.push_bytes(&mut buf, 4);
-            assert!(buf == ~[8, 9, 10, 11]);
-        })
+        assert!(reader.push_bytes(&mut buf, 4).is_err());
+        assert!(buf == ~[8, 9, 10, 11]);
     }
 
     #[test]
@@ -340,38 +326,16 @@ mod test {
             count: 0,
         };
         let mut buf = ~[8, 9];
-        io_error::cond.trap(|_| { } ).inside(|| {
-            reader.push_bytes(&mut buf, 4);
-        });
+        assert!(reader.push_bytes(&mut buf, 4).is_err());
         assert!(buf == ~[8, 9, 10]);
     }
 
-    #[test]
-    #[should_fail]
-    #[ignore] // borrow issues with RefCell
-    fn push_bytes_fail_reset_len() {
-        // push_bytes unsafely sets the vector length. This is testing that
-        // upon failure the length is reset correctly.
-        let _reader = ErroringLaterReader {
-            count: 0,
-        };
-        // FIXME (#7049): Figure out some other way to do this.
-        //let buf = RefCell::new(~[8, 9]);
-        (|| {
-            //reader.push_bytes(buf.borrow_mut().get(), 4);
-        }).finally(|| {
-            // NB: Using rtassert here to trigger abort on failure since this is a should_fail test
-            // FIXME: #7049 This fails because buf is still borrowed
-            //rtassert!(buf.borrow().get() == ~[8, 9, 10]);
-        })
-    }
-
     #[test]
     fn read_to_end() {
         let mut reader = ThreeChunkReader {
             count: 0,
         };
-        let buf = reader.read_to_end();
+        let buf = reader.read_to_end().unwrap();
         assert!(buf == ~[10, 11, 12, 13]);
     }
 
@@ -381,7 +345,7 @@ mod test {
         let mut reader = ThreeChunkReader {
             count: 0,
         };
-        let buf = reader.read_to_end();
+        let buf = reader.read_to_end().unwrap();
         assert!(buf == ~[10, 11]);
     }
 
@@ -391,12 +355,12 @@ mod test {
 
         let mut writer = MemWriter::new();
         for i in uints.iter() {
-            writer.write_le_u64(*i);
+            writer.write_le_u64(*i).unwrap();
         }
 
         let mut reader = MemReader::new(writer.unwrap());
         for i in uints.iter() {
-            assert!(reader.read_le_u64() == *i);
+            assert!(reader.read_le_u64().unwrap() == *i);
         }
     }
 
@@ -407,12 +371,12 @@ mod test {
 
         let mut writer = MemWriter::new();
         for i in uints.iter() {
-            writer.write_be_u64(*i);
+            writer.write_be_u64(*i).unwrap();
         }
 
         let mut reader = MemReader::new(writer.unwrap());
         for i in uints.iter() {
-            assert!(reader.read_be_u64() == *i);
+            assert!(reader.read_be_u64().unwrap() == *i);
         }
     }
 
@@ -422,14 +386,14 @@ mod test {
 
         let mut writer = MemWriter::new();
         for i in ints.iter() {
-            writer.write_be_i32(*i);
+            writer.write_be_i32(*i).unwrap();
         }
 
         let mut reader = MemReader::new(writer.unwrap());
         for i in ints.iter() {
             // this tests that the sign extension is working
             // (comparing the values as i32 would not test this)
-            assert!(reader.read_be_int_n(4) == *i as i64);
+            assert!(reader.read_be_int_n(4).unwrap() == *i as i64);
         }
     }
 
@@ -439,10 +403,10 @@ mod test {
         let buf = ~[0x41, 0x02, 0x00, 0x00];
 
         let mut writer = MemWriter::new();
-        writer.write(buf);
+        writer.write(buf).unwrap();
 
         let mut reader = MemReader::new(writer.unwrap());
-        let f = reader.read_be_f32();
+        let f = reader.read_be_f32().unwrap();
         assert!(f == 8.1250);
     }
 
@@ -451,12 +415,12 @@ mod test {
         let f:f32 = 8.1250;
 
         let mut writer = MemWriter::new();
-        writer.write_be_f32(f);
-        writer.write_le_f32(f);
+        writer.write_be_f32(f).unwrap();
+        writer.write_le_f32(f).unwrap();
 
         let mut reader = MemReader::new(writer.unwrap());
-        assert!(reader.read_be_f32() == 8.1250);
-        assert!(reader.read_le_f32() == 8.1250);
+        assert!(reader.read_be_f32().unwrap() == 8.1250);
+        assert!(reader.read_le_f32().unwrap() == 8.1250);
     }
 
     #[test]

src/libstd/io/mem.rs

@@ -13,9 +13,10 @@
 use cmp::max;
 use cmp::min;
 use container::Container;
-use option::{Option, Some, None};
-use super::{Reader, Writer, Seek, Buffer, IoError, SeekStyle, io_error,
-            OtherIoError};
+use option::None;
+use result::{Err, Ok};
+use io;
+use io::{Reader, Writer, Seek, Buffer, IoError, SeekStyle, IoResult};
 use vec;
 use vec::{Vector, ImmutableVector, MutableVector, OwnedCloneableVector};
 
@@ -24,6 +25,7 @@ use vec::{Vector, ImmutableVector, MutableVector, OwnedCloneableVector};
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::MemWriter;
 ///
 /// let mut w = MemWriter::new();
@@ -59,7 +61,7 @@ impl MemWriter {
 }
 
 impl Writer for MemWriter {
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
         // Make sure the internal buffer is as least as big as where we
         // currently are
         let difference = self.pos as i64 - self.buf.len() as i64;
@@ -86,14 +88,15 @@ impl Writer for MemWriter {
 
         // Bump us forward
         self.pos += buf.len();
+        Ok(())
     }
 }
 
 // FIXME(#10432)
 impl Seek for MemWriter {
-    fn tell(&self) -> u64 { self.pos as u64 }
+    fn tell(&self) -> IoResult<u64> { Ok(self.pos as u64) }
 
-    fn seek(&mut self, pos: i64, style: SeekStyle) {
+    fn seek(&mut self, pos: i64, style: SeekStyle) -> IoResult<()> {
         // compute offset as signed and clamp to prevent overflow
         let offset = match style {
             SeekSet => { 0 }
@@ -102,6 +105,7 @@ impl Seek for MemWriter {
         } as i64;
 
         self.pos = max(0, offset+pos) as uint;
+        Ok(())
     }
 }
 
@@ -110,11 +114,12 @@ impl Seek for MemWriter {
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::MemReader;
 ///
 /// let mut r = MemReader::new(~[0, 1, 2]);
 ///
-/// assert_eq!(r.read_to_end(), ~[0, 1, 2]);
+/// assert_eq!(r.read_to_end().unwrap(), ~[0, 1, 2]);
 /// ```
 pub struct MemReader {
     priv buf: ~[u8],
@@ -148,8 +153,8 @@ impl MemReader {
 }
 
 impl Reader for MemReader {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        if self.eof() { return None }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
+        if self.eof() { return Err(io::standard_error(io::EndOfFile)) }
 
         let write_len = min(buf.len(), self.buf.len() - self.pos);
         {
@@ -161,28 +166,31 @@ impl Reader for MemReader {
         self.pos += write_len;
         assert!(self.pos <= self.buf.len());
 
-        return Some(write_len);
+        return Ok(write_len);
     }
 }
 
 impl Seek for MemReader {
-    fn tell(&self) -> u64 { self.pos as u64 }
-    fn seek(&mut self, _pos: i64, _style: SeekStyle) { fail!() }
+    fn tell(&self) -> IoResult<u64> { Ok(self.pos as u64) }
+    fn seek(&mut self, _pos: i64, _style: SeekStyle) -> IoResult<()> { fail!() }
 }
 
 impl Buffer for MemReader {
-    fn fill<'a>(&'a mut self) -> &'a [u8] { self.buf.slice_from(self.pos) }
+    fn fill<'a>(&'a mut self) -> IoResult<&'a [u8]> {
+        Ok(self.buf.slice_from(self.pos))
+    }
     fn consume(&mut self, amt: uint) { self.pos += amt; }
 }
 
 /// Writes to a fixed-size byte slice
 ///
-/// If a write will not fit in the buffer, it raises the `io_error`
-/// condition and does not write any data.
+/// If a write will not fit in the buffer, it returns an error and does not
+/// write any data.
 ///
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::BufWriter;
 ///
 /// let mut buf = [0, ..4];
@@ -207,28 +215,28 @@ impl<'a> BufWriter<'a> {
 }
 
 impl<'a> Writer for BufWriter<'a> {
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
         // raises a condition if the entire write does not fit in the buffer
         let max_size = self.buf.len();
         if self.pos >= max_size || (self.pos + buf.len()) > max_size {
-            io_error::cond.raise(IoError {
-                kind: OtherIoError,
+            return Err(IoError {
+                kind: io::OtherIoError,
                 desc: "Trying to write past end of buffer",
                 detail: None
-            });
-            return;
+            })
         }
 
         vec::bytes::copy_memory(self.buf.mut_slice_from(self.pos), buf);
         self.pos += buf.len();
+        Ok(())
     }
 }
 
 // FIXME(#10432)
 impl<'a> Seek for BufWriter<'a> {
-    fn tell(&self) -> u64 { self.pos as u64 }
+    fn tell(&self) -> IoResult<u64> { Ok(self.pos as u64) }
 
-    fn seek(&mut self, pos: i64, style: SeekStyle) {
+    fn seek(&mut self, pos: i64, style: SeekStyle) -> IoResult<()> {
         // compute offset as signed and clamp to prevent overflow
         let offset = match style {
             SeekSet => { 0 }
@@ -237,6 +245,7 @@ impl<'a> Seek for BufWriter<'a> {
         } as i64;
 
         self.pos = max(0, offset+pos) as uint;
+        Ok(())
     }
 }
 
@@ -246,12 +255,13 @@ impl<'a> Seek for BufWriter<'a> {
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::BufReader;
 ///
 /// let mut buf = [0, 1, 2, 3];
 /// let mut r = BufReader::new(buf);
 ///
-/// assert_eq!(r.read_to_end(), ~[0, 1, 2, 3]);
+/// assert_eq!(r.read_to_end().unwrap(), ~[0, 1, 2, 3]);
 /// ```
 pub struct BufReader<'a> {
     priv buf: &'a [u8],
@@ -274,8 +284,8 @@ impl<'a> BufReader<'a> {
 }
 
 impl<'a> Reader for BufReader<'a> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        if self.eof() { return None }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
+        if self.eof() { return Err(io::standard_error(io::EndOfFile)) }
 
         let write_len = min(buf.len(), self.buf.len() - self.pos);
         {
@@ -287,18 +297,19 @@ impl<'a> Reader for BufReader<'a> {
         self.pos += write_len;
         assert!(self.pos <= self.buf.len());
 
-        return Some(write_len);
+        return Ok(write_len);
      }
 }
 
 impl<'a> Seek for BufReader<'a> {
-    fn tell(&self) -> u64 { self.pos as u64 }
-
-    fn seek(&mut self, _pos: i64, _style: SeekStyle) { fail!() }
+    fn tell(&self) -> IoResult<u64> { Ok(self.pos as u64) }
+    fn seek(&mut self, _pos: i64, _style: SeekStyle) -> IoResult<()> { fail!() }
 }
 
 impl<'a> Buffer for BufReader<'a> {
-    fn fill<'a>(&'a mut self) -> &'a [u8] { self.buf.slice_from(self.pos) }
+    fn fill<'a>(&'a mut self) -> IoResult<&'a [u8]> {
+        Ok(self.buf.slice_from(self.pos))
+    }
     fn consume(&mut self, amt: uint) { self.pos += amt; }
 }
 
@@ -307,33 +318,34 @@ mod test {
     use prelude::*;
     use super::*;
     use io::*;
+    use io;
 
     #[test]
     fn test_mem_writer() {
         let mut writer = MemWriter::new();
-        assert_eq!(writer.tell(), 0);
-        writer.write([0]);
-        assert_eq!(writer.tell(), 1);
-        writer.write([1, 2, 3]);
-        writer.write([4, 5, 6, 7]);
-        assert_eq!(writer.tell(), 8);
+        assert_eq!(writer.tell(), Ok(0));
+        writer.write([0]).unwrap();
+        assert_eq!(writer.tell(), Ok(1));
+        writer.write([1, 2, 3]).unwrap();
+        writer.write([4, 5, 6, 7]).unwrap();
+        assert_eq!(writer.tell(), Ok(8));
         assert_eq!(writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7]);
 
-        writer.seek(0, SeekSet);
-        assert_eq!(writer.tell(), 0);
-        writer.write([3, 4]);
+        writer.seek(0, SeekSet).unwrap();
+        assert_eq!(writer.tell(), Ok(0));
+        writer.write([3, 4]).unwrap();
         assert_eq!(writer.get_ref(), [3, 4, 2, 3, 4, 5, 6, 7]);
 
-        writer.seek(1, SeekCur);
-        writer.write([0, 1]);
+        writer.seek(1, SeekCur).unwrap();
+        writer.write([0, 1]).unwrap();
         assert_eq!(writer.get_ref(), [3, 4, 2, 0, 1, 5, 6, 7]);
 
-        writer.seek(-1, SeekEnd);
-        writer.write([1, 2]);
+        writer.seek(-1, SeekEnd).unwrap();
+        writer.write([1, 2]).unwrap();
         assert_eq!(writer.get_ref(), [3, 4, 2, 0, 1, 5, 6, 1, 2]);
 
-        writer.seek(1, SeekEnd);
-        writer.write([1]);
+        writer.seek(1, SeekEnd).unwrap();
+        writer.write([1]).unwrap();
         assert_eq!(writer.get_ref(), [3, 4, 2, 0, 1, 5, 6, 1, 2, 0, 1]);
     }
 
@@ -342,12 +354,12 @@ mod test {
         let mut buf = [0 as u8, ..8];
         {
             let mut writer = BufWriter::new(buf);
-            assert_eq!(writer.tell(), 0);
-            writer.write([0]);
-            assert_eq!(writer.tell(), 1);
-            writer.write([1, 2, 3]);
-            writer.write([4, 5, 6, 7]);
-            assert_eq!(writer.tell(), 8);
+            assert_eq!(writer.tell(), Ok(0));
+            writer.write([0]).unwrap();
+            assert_eq!(writer.tell(), Ok(1));
+            writer.write([1, 2, 3]).unwrap();
+            writer.write([4, 5, 6, 7]).unwrap();
+            assert_eq!(writer.tell(), Ok(8));
         }
         assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7]);
     }
@@ -357,24 +369,24 @@ mod test {
         let mut buf = [0 as u8, ..8];
         {
             let mut writer = BufWriter::new(buf);
-            assert_eq!(writer.tell(), 0);
-            writer.write([1]);
-            assert_eq!(writer.tell(), 1);
+            assert_eq!(writer.tell(), Ok(0));
+            writer.write([1]).unwrap();
+            assert_eq!(writer.tell(), Ok(1));
 
-            writer.seek(2, SeekSet);
-            assert_eq!(writer.tell(), 2);
-            writer.write([2]);
-            assert_eq!(writer.tell(), 3);
+            writer.seek(2, SeekSet).unwrap();
+            assert_eq!(writer.tell(), Ok(2));
+            writer.write([2]).unwrap();
+            assert_eq!(writer.tell(), Ok(3));
 
-            writer.seek(-2, SeekCur);
-            assert_eq!(writer.tell(), 1);
-            writer.write([3]);
-            assert_eq!(writer.tell(), 2);
+            writer.seek(-2, SeekCur).unwrap();
+            assert_eq!(writer.tell(), Ok(1));
+            writer.write([3]).unwrap();
+            assert_eq!(writer.tell(), Ok(2));
 
-            writer.seek(-1, SeekEnd);
-            assert_eq!(writer.tell(), 7);
-            writer.write([4]);
-            assert_eq!(writer.tell(), 8);
+            writer.seek(-1, SeekEnd).unwrap();
+            assert_eq!(writer.tell(), Ok(7));
+            writer.write([4]).unwrap();
+            assert_eq!(writer.tell(), Ok(8));
 
         }
         assert_eq!(buf, [1, 3, 2, 0, 0, 0, 0, 4]);
@@ -384,35 +396,31 @@ mod test {
     fn test_buf_writer_error() {
         let mut buf = [0 as u8, ..2];
         let mut writer = BufWriter::new(buf);
-        writer.write([0]);
+        writer.write([0]).unwrap();
 
-        let mut called = false;
-        io_error::cond.trap(|err| {
-            assert_eq!(err.kind, OtherIoError);
-            called = true;
-        }).inside(|| {
-            writer.write([0, 0]);
-        });
-        assert!(called);
+        match writer.write([0, 0]) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::OtherIoError),
+        }
     }
 
     #[test]
     fn test_mem_reader() {
         let mut reader = MemReader::new(~[0, 1, 2, 3, 4, 5, 6, 7]);
         let mut buf = [];
-        assert_eq!(reader.read(buf), Some(0));
-        assert_eq!(reader.tell(), 0);
+        assert_eq!(reader.read(buf), Ok(0));
+        assert_eq!(reader.tell(), Ok(0));
         let mut buf = [0];
-        assert_eq!(reader.read(buf), Some(1));
-        assert_eq!(reader.tell(), 1);
+        assert_eq!(reader.read(buf), Ok(1));
+        assert_eq!(reader.tell(), Ok(1));
         assert_eq!(buf, [0]);
         let mut buf = [0, ..4];
-        assert_eq!(reader.read(buf), Some(4));
-        assert_eq!(reader.tell(), 5);
+        assert_eq!(reader.read(buf), Ok(4));
+        assert_eq!(reader.tell(), Ok(5));
         assert_eq!(buf, [1, 2, 3, 4]);
-        assert_eq!(reader.read(buf), Some(3));
+        assert_eq!(reader.read(buf), Ok(3));
         assert_eq!(buf.slice(0, 3), [5, 6, 7]);
-        assert_eq!(reader.read(buf), None);
+        assert!(reader.read(buf).is_err());
     }
 
     #[test]
@@ -420,64 +428,64 @@ mod test {
         let in_buf = ~[0, 1, 2, 3, 4, 5, 6, 7];
         let mut reader = BufReader::new(in_buf);
         let mut buf = [];
-        assert_eq!(reader.read(buf), Some(0));
-        assert_eq!(reader.tell(), 0);
+        assert_eq!(reader.read(buf), Ok(0));
+        assert_eq!(reader.tell(), Ok(0));
         let mut buf = [0];
-        assert_eq!(reader.read(buf), Some(1));
-        assert_eq!(reader.tell(), 1);
+        assert_eq!(reader.read(buf), Ok(1));
+        assert_eq!(reader.tell(), Ok(1));
         assert_eq!(buf, [0]);
         let mut buf = [0, ..4];
-        assert_eq!(reader.read(buf), Some(4));
-        assert_eq!(reader.tell(), 5);
+        assert_eq!(reader.read(buf), Ok(4));
+        assert_eq!(reader.tell(), Ok(5));
         assert_eq!(buf, [1, 2, 3, 4]);
-        assert_eq!(reader.read(buf), Some(3));
+        assert_eq!(reader.read(buf), Ok(3));
         assert_eq!(buf.slice(0, 3), [5, 6, 7]);
-        assert_eq!(reader.read(buf), None);
+        assert!(reader.read(buf).is_err());
     }
 
     #[test]
     fn test_read_char() {
         let b = bytes!("Việt");
         let mut r = BufReader::new(b);
-        assert_eq!(r.read_char(), Some('V'));
-        assert_eq!(r.read_char(), Some('i'));
-        assert_eq!(r.read_char(), Some('ệ'));
-        assert_eq!(r.read_char(), Some('t'));
-        assert_eq!(r.read_char(), None);
+        assert_eq!(r.read_char(), Ok('V'));
+        assert_eq!(r.read_char(), Ok('i'));
+        assert_eq!(r.read_char(), Ok('ệ'));
+        assert_eq!(r.read_char(), Ok('t'));
+        assert!(r.read_char().is_err());
     }
 
     #[test]
     fn test_read_bad_char() {
         let b = bytes!(0x80);
         let mut r = BufReader::new(b);
-        assert_eq!(r.read_char(), None);
+        assert!(r.read_char().is_err());
     }
 
     #[test]
     fn test_write_strings() {
         let mut writer = MemWriter::new();
-        writer.write_str("testing");
-        writer.write_line("testing");
-        writer.write_str("testing");
+        writer.write_str("testing").unwrap();
+        writer.write_line("testing").unwrap();
+        writer.write_str("testing").unwrap();
         let mut r = BufReader::new(writer.get_ref());
-        assert_eq!(r.read_to_str(), ~"testingtesting\ntesting");
+        assert_eq!(r.read_to_str().unwrap(), ~"testingtesting\ntesting");
     }
 
     #[test]
     fn test_write_char() {
         let mut writer = MemWriter::new();
-        writer.write_char('a');
-        writer.write_char('\n');
-        writer.write_char('ệ');
+        writer.write_char('a').unwrap();
+        writer.write_char('\n').unwrap();
+        writer.write_char('ệ').unwrap();
         let mut r = BufReader::new(writer.get_ref());
-        assert_eq!(r.read_to_str(), ~"a\nệ");
+        assert_eq!(r.read_to_str().unwrap(), ~"a\nệ");
     }
 
     #[test]
     fn test_read_whole_string_bad() {
         let buf = [0xff];
         let mut r = BufReader::new(buf);
-        match result(|| r.read_to_str()) {
+        match r.read_to_str() {
             Ok(..) => fail!(),
             Err(..) => {}
         }

src/libstd/io/net/addrinfo.rs

@@ -17,8 +17,9 @@ getaddrinfo()
 
 */
 
-use option::{Option, Some, None};
+use io::IoResult;
 use io::net::ip::{SocketAddr, IpAddr};
+use option::{Option, Some, None};
 use rt::rtio::{IoFactory, LocalIo};
 use vec::ImmutableVector;
 
@@ -69,11 +70,7 @@ pub struct Info {
 
 /// Easy name resolution. Given a hostname, returns the list of IP addresses for
 /// that hostname.
-///
-/// # Failure
-///
-/// On failure, this will raise on the `io_error` condition.
-pub fn get_host_addresses(host: &str) -> Option<~[IpAddr]> {
+pub fn get_host_addresses(host: &str) -> IoResult<~[IpAddr]> {
     lookup(Some(host), None, None).map(|a| a.map(|i| i.address.ip))
 }
 
@@ -87,14 +84,10 @@ pub fn get_host_addresses(host: &str) -> Option<~[IpAddr]> {
 /// * hint - see the hint structure, and "man -s 3 getaddrinfo", for how this
 ///          controls lookup
 ///
-/// # Failure
-///
-/// On failure, this will raise on the `io_error` condition.
-///
 /// FIXME: this is not public because the `Hint` structure is not ready for public
 ///      consumption just yet.
 fn lookup(hostname: Option<&str>, servname: Option<&str>, hint: Option<Hint>)
-          -> Option<~[Info]> {
+          -> IoResult<~[Info]> {
     LocalIo::maybe_raise(|io| io.get_host_addresses(hostname, servname, hint))
 }
 
@@ -115,6 +108,6 @@ mod test {
     iotest!(fn issue_10663() {
         // Something should happen here, but this certainly shouldn't cause
         // everything to die. The actual outcome we don't care too much about.
-        get_host_addresses("example.com");
+        get_host_addresses("example.com").unwrap();
     } #[ignore])
 }

src/libstd/io/net/tcp.rs

@@ -8,11 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use option::{Option, Some, None};
-use result::{Ok, Err};
 use io::net::ip::SocketAddr;
-use io::{Reader, Writer, Listener, Acceptor};
-use io::{io_error, EndOfFile};
+use io::{Reader, Writer, Listener, Acceptor, IoResult};
 use rt::rtio::{IoFactory, LocalIo, RtioSocket, RtioTcpListener};
 use rt::rtio::{RtioTcpAcceptor, RtioTcpStream};
 
@@ -25,57 +22,27 @@ impl TcpStream {
         TcpStream { obj: s }
     }
 
-    pub fn connect(addr: SocketAddr) -> Option<TcpStream> {
+    pub fn connect(addr: SocketAddr) -> IoResult<TcpStream> {
         LocalIo::maybe_raise(|io| {
             io.tcp_connect(addr).map(TcpStream::new)
         })
     }
 
-    pub fn peer_name(&mut self) -> Option<SocketAddr> {
-        match self.obj.peer_name() {
-            Ok(pn) => Some(pn),
-            Err(ioerr) => {
-                debug!("failed to get peer name: {:?}", ioerr);
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    pub fn peer_name(&mut self) -> IoResult<SocketAddr> {
+        self.obj.peer_name()
     }
 
-    pub fn socket_name(&mut self) -> Option<SocketAddr> {
-        match self.obj.socket_name() {
-            Ok(sn) => Some(sn),
-            Err(ioerr) => {
-                debug!("failed to get socket name: {:?}", ioerr);
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    pub fn socket_name(&mut self) -> IoResult<SocketAddr> {
+        self.obj.socket_name()
     }
 }
 
 impl Reader for TcpStream {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        match self.obj.read(buf) {
-            Ok(read) => Some(read),
-            Err(ioerr) => {
-                // EOF is indicated by returning None
-                if ioerr.kind != EndOfFile {
-                    io_error::cond.raise(ioerr);
-                }
-                return None;
-            }
-        }
-    }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> { self.obj.read(buf) }
 }
 
 impl Writer for TcpStream {
-    fn write(&mut self, buf: &[u8]) {
-        match self.obj.write(buf) {
-            Ok(_) => (),
-            Err(ioerr) => io_error::cond.raise(ioerr),
-        }
-    }
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.obj.write(buf) }
 }
 
 pub struct TcpListener {
@@ -83,33 +50,20 @@ pub struct TcpListener {
 }
 
 impl TcpListener {
-    pub fn bind(addr: SocketAddr) -> Option<TcpListener> {
+    pub fn bind(addr: SocketAddr) -> IoResult<TcpListener> {
         LocalIo::maybe_raise(|io| {
             io.tcp_bind(addr).map(|l| TcpListener { obj: l })
         })
     }
 
-    pub fn socket_name(&mut self) -> Option<SocketAddr> {
-        match self.obj.socket_name() {
-            Ok(sn) => Some(sn),
-            Err(ioerr) => {
-                debug!("failed to get socket name: {:?}", ioerr);
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    pub fn socket_name(&mut self) -> IoResult<SocketAddr> {
+        self.obj.socket_name()
     }
 }
 
 impl Listener<TcpStream, TcpAcceptor> for TcpListener {
-    fn listen(self) -> Option<TcpAcceptor> {
-        match self.obj.listen() {
-            Ok(acceptor) => Some(TcpAcceptor { obj: acceptor }),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    fn listen(self) -> IoResult<TcpAcceptor> {
+        self.obj.listen().map(|acceptor| TcpAcceptor { obj: acceptor })
     }
 }
 
@@ -118,14 +72,8 @@ pub struct TcpAcceptor {
 }
 
 impl Acceptor<TcpStream> for TcpAcceptor {
-    fn accept(&mut self) -> Option<TcpStream> {
-        match self.obj.accept() {
-            Ok(s) => Some(TcpStream::new(s)),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    fn accept(&mut self) -> IoResult<TcpStream> {
+        self.obj.accept().map(TcpStream::new)
     }
 }
 
@@ -138,29 +86,19 @@ mod test {
 
     // FIXME #11530 this fails on android because tests are run as root
     iotest!(fn bind_error() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert!(e.kind == PermissionDenied);
-            called = true;
-        }).inside(|| {
-            let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
-            let listener = TcpListener::bind(addr);
-            assert!(listener.is_none());
-        });
-        assert!(called);
+        let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
+        match TcpListener::bind(addr) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, PermissionDenied),
+        }
     } #[ignore(cfg(windows))] #[ignore(cfg(target_os = "android"))])
 
     iotest!(fn connect_error() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert_eq!(e.kind, ConnectionRefused);
-            called = true;
-        }).inside(|| {
-            let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
-            let stream = TcpStream::connect(addr);
-            assert!(stream.is_none());
-        });
-        assert!(called);
+        let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
+        match TcpStream::connect(addr) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, ConnectionRefused),
+        }
     })
 
     iotest!(fn smoke_test_ip4() {
@@ -170,14 +108,14 @@ mod test {
         spawn(proc() {
             port.recv();
             let mut stream = TcpStream::connect(addr);
-            stream.write([99]);
+            stream.write([99]).unwrap();
         });
 
         let mut acceptor = TcpListener::bind(addr).listen();
         chan.send(());
         let mut stream = acceptor.accept();
         let mut buf = [0];
-        stream.read(buf);
+        stream.read(buf).unwrap();
         assert!(buf[0] == 99);
     })
 
@@ -188,14 +126,14 @@ mod test {
         spawn(proc() {
             port.recv();
             let mut stream = TcpStream::connect(addr);
-            stream.write([99]);
+            stream.write([99]).unwrap();
         });
 
         let mut acceptor = TcpListener::bind(addr).listen();
         chan.send(());
         let mut stream = acceptor.accept();
         let mut buf = [0];
-        stream.read(buf);
+        stream.read(buf).unwrap();
         assert!(buf[0] == 99);
     })
 
@@ -214,7 +152,7 @@ mod test {
         let mut stream = acceptor.accept();
         let mut buf = [0];
         let nread = stream.read(buf);
-        assert!(nread.is_none());
+        assert!(nread.is_err());
     })
 
     iotest!(fn read_eof_ip6() {
@@ -232,7 +170,7 @@ mod test {
         let mut stream = acceptor.accept();
         let mut buf = [0];
         let nread = stream.read(buf);
-        assert!(nread.is_none());
+        assert!(nread.is_err());
     })
 
     iotest!(fn read_eof_twice_ip4() {
@@ -250,17 +188,15 @@ mod test {
         let mut stream = acceptor.accept();
         let mut buf = [0];
         let nread = stream.read(buf);
-        assert!(nread.is_none());
-        io_error::cond.trap(|e| {
-            if cfg!(windows) {
-                assert_eq!(e.kind, NotConnected);
-            } else {
-                fail!();
+        assert!(nread.is_err());
+
+        match stream.read(buf) {
+            Ok(..) => fail!(),
+            Err(ref e) => {
+                assert!(e.kind == NotConnected || e.kind == EndOfFile,
+                        "unknown kind: {:?}", e.kind);
             }
-        }).inside(|| {
-            let nread = stream.read(buf);
-            assert!(nread.is_none());
-        })
+        }
     })
 
     iotest!(fn read_eof_twice_ip6() {
@@ -278,17 +214,15 @@ mod test {
         let mut stream = acceptor.accept();
         let mut buf = [0];
         let nread = stream.read(buf);
-        assert!(nread.is_none());
-        io_error::cond.trap(|e| {
-            if cfg!(windows) {
-                assert_eq!(e.kind, NotConnected);
-            } else {
-                fail!();
+        assert!(nread.is_err());
+
+        match stream.read(buf) {
+            Ok(..) => fail!(),
+            Err(ref e) => {
+                assert!(e.kind == NotConnected || e.kind == EndOfFile,
+                        "unknown kind: {:?}", e.kind);
             }
-        }).inside(|| {
-            let nread = stream.read(buf);
-            assert!(nread.is_none());
-        })
+        }
     })
 
     iotest!(fn write_close_ip4() {
@@ -306,19 +240,16 @@ mod test {
         let mut stream = acceptor.accept();
         let buf = [0];
         loop {
-            let mut stop = false;
-            io_error::cond.trap(|e| {
-                // NB: ECONNRESET on linux, EPIPE on mac, ECONNABORTED
-                //     on windows
-                assert!(e.kind == ConnectionReset ||
-                        e.kind == BrokenPipe ||
-                        e.kind == ConnectionAborted,
-                        "unknown error: {:?}", e);
-                stop = true;
-            }).inside(|| {
-                stream.write(buf);
-            });
-            if stop { break }
+            match stream.write(buf) {
+                Ok(..) => {}
+                Err(e) => {
+                    assert!(e.kind == ConnectionReset ||
+                            e.kind == BrokenPipe ||
+                            e.kind == ConnectionAborted,
+                            "unknown error: {:?}", e);
+                    break;
+                }
+            }
         }
     })
 
@@ -337,19 +268,16 @@ mod test {
         let mut stream = acceptor.accept();
         let buf = [0];
         loop {
-            let mut stop = false;
-            io_error::cond.trap(|e| {
-                // NB: ECONNRESET on linux, EPIPE on mac, ECONNABORTED
-                //     on windows
-                assert!(e.kind == ConnectionReset ||
-                        e.kind == BrokenPipe ||
-                        e.kind == ConnectionAborted,
-                        "unknown error: {:?}", e);
-                stop = true;
-            }).inside(|| {
-                stream.write(buf);
-            });
-            if stop { break }
+            match stream.write(buf) {
+                Ok(..) => {}
+                Err(e) => {
+                    assert!(e.kind == ConnectionReset ||
+                            e.kind == BrokenPipe ||
+                            e.kind == ConnectionAborted,
+                            "unknown error: {:?}", e);
+                    break;
+                }
+            }
         }
     })
 
@@ -362,7 +290,7 @@ mod test {
             port.recv();
             for _ in range(0, max) {
                 let mut stream = TcpStream::connect(addr);
-                stream.write([99]);
+                stream.write([99]).unwrap();
             }
         });
 
@@ -370,7 +298,7 @@ mod test {
         chan.send(());
         for ref mut stream in acceptor.incoming().take(max) {
             let mut buf = [0];
-            stream.read(buf);
+            stream.read(buf).unwrap();
             assert_eq!(buf[0], 99);
         }
     })
@@ -384,7 +312,7 @@ mod test {
             port.recv();
             for _ in range(0, max) {
                 let mut stream = TcpStream::connect(addr);
-                stream.write([99]);
+                stream.write([99]).unwrap();
             }
         });
 
@@ -392,7 +320,7 @@ mod test {
         chan.send(());
         for ref mut stream in acceptor.incoming().take(max) {
             let mut buf = [0];
-            stream.read(buf);
+            stream.read(buf).unwrap();
             assert_eq!(buf[0], 99);
         }
     })
@@ -410,7 +338,7 @@ mod test {
                 spawn(proc() {
                     let mut stream = stream;
                     let mut buf = [0];
-                    stream.read(buf);
+                    stream.read(buf).unwrap();
                     assert!(buf[0] == i as u8);
                     debug!("read");
                 });
@@ -429,7 +357,7 @@ mod test {
                 // Connect again before writing
                 connect(i + 1, addr);
                 debug!("writing");
-                stream.write([i as u8]);
+                stream.write([i as u8]).unwrap();
             });
         }
     })
@@ -447,7 +375,7 @@ mod test {
                 spawn(proc() {
                     let mut stream = stream;
                     let mut buf = [0];
-                    stream.read(buf);
+                    stream.read(buf).unwrap();
                     assert!(buf[0] == i as u8);
                     debug!("read");
                 });
@@ -466,7 +394,7 @@ mod test {
                 // Connect again before writing
                 connect(i + 1, addr);
                 debug!("writing");
-                stream.write([i as u8]);
+                stream.write([i as u8]).unwrap();
             });
         }
     })
@@ -484,7 +412,7 @@ mod test {
                 spawn(proc() {
                     let mut stream = stream;
                     let mut buf = [0];
-                    stream.read(buf);
+                    stream.read(buf).unwrap();
                     assert!(buf[0] == 99);
                     debug!("read");
                 });
@@ -503,7 +431,7 @@ mod test {
                 // Connect again before writing
                 connect(i + 1, addr);
                 debug!("writing");
-                stream.write([99]);
+                stream.write([99]).unwrap();
             });
         }
     })
@@ -521,7 +449,7 @@ mod test {
                 spawn(proc() {
                     let mut stream = stream;
                     let mut buf = [0];
-                    stream.read(buf);
+                    stream.read(buf).unwrap();
                     assert!(buf[0] == 99);
                     debug!("read");
                 });
@@ -540,7 +468,7 @@ mod test {
                 // Connect again before writing
                 connect(i + 1, addr);
                 debug!("writing");
-                stream.write([99]);
+                stream.write([99]).unwrap();
             });
         }
     })
@@ -551,7 +479,7 @@ mod test {
         // Make sure socket_name gives
         // us the socket we binded to.
         let so_name = listener.socket_name();
-        assert!(so_name.is_some());
+        assert!(so_name.is_ok());
         assert_eq!(addr, so_name.unwrap());
     }
 
@@ -561,20 +489,20 @@ mod test {
         spawn(proc() {
             let mut acceptor = TcpListener::bind(addr).listen();
             chan.send(());
-            acceptor.accept();
+            acceptor.accept().unwrap();
         });
 
         port.recv();
         let stream = TcpStream::connect(addr);
 
-        assert!(stream.is_some());
+        assert!(stream.is_ok());
         let mut stream = stream.unwrap();
 
         // Make sure peer_name gives us the
         // address/port of the peer we've
         // connected to.
         let peer_name = stream.peer_name();
-        assert!(peer_name.is_some());
+        assert!(peer_name.is_ok());
         assert_eq!(addr, peer_name.unwrap());
     }
 
@@ -593,37 +521,33 @@ mod test {
         let addr = next_test_ip4();
         let (p, c) = Chan::new();
         spawn(proc() {
-            let mut srv = TcpListener::bind(addr).listen();
+            let mut srv = TcpListener::bind(addr).listen().unwrap();
             c.send(());
             let mut cl = srv.accept().unwrap();
-            cl.write([10]);
+            cl.write([10]).unwrap();
             let mut b = [0];
-            cl.read(b);
+            cl.read(b).unwrap();
             c.send(());
         });
 
         p.recv();
         let mut c = TcpStream::connect(addr).unwrap();
         let mut b = [0, ..10];
-        assert_eq!(c.read(b), Some(1));
-        c.write([1]);
+        assert_eq!(c.read(b), Ok(1));
+        c.write([1]).unwrap();
         p.recv();
     })
 
     iotest!(fn double_bind() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert!(e.kind == ConnectionRefused || e.kind == OtherIoError);
-            called = true;
-        }).inside(|| {
-            let addr = next_test_ip4();
-            let listener = TcpListener::bind(addr).unwrap().listen();
-            assert!(listener.is_some());
-            let listener2 = TcpListener::bind(addr).and_then(|l|
-                                                    l.listen());
-            assert!(listener2.is_none());
-        });
-        assert!(called);
+        let addr = next_test_ip4();
+        let listener = TcpListener::bind(addr).unwrap().listen();
+        assert!(listener.is_ok());
+        match TcpListener::bind(addr).listen() {
+            Ok(..) => fail!(),
+            Err(e) => {
+                assert!(e.kind == ConnectionRefused || e.kind == OtherIoError);
+            }
+        }
     })
 
     iotest!(fn fast_rebind() {
@@ -632,7 +556,7 @@ mod test {
 
         spawn(proc() {
             port.recv();
-            let _stream = TcpStream::connect(addr);
+            let _stream = TcpStream::connect(addr).unwrap();
             // Close
             port.recv();
         });
@@ -641,7 +565,7 @@ mod test {
             let mut acceptor = TcpListener::bind(addr).listen();
             chan.send(());
             {
-                let _stream = acceptor.accept();
+                let _stream = acceptor.accept().unwrap();
                 // Close client
                 chan.send(());
             }

src/libstd/io/net/udp.rs

@@ -8,11 +8,9 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use option::{Option, Some, None};
 use result::{Ok, Err};
 use io::net::ip::SocketAddr;
-use io::{Reader, Writer};
-use io::{io_error, EndOfFile};
+use io::{Reader, Writer, IoResult};
 use rt::rtio::{RtioSocket, RtioUdpSocket, IoFactory, LocalIo};
 
 pub struct UdpSocket {
@@ -20,45 +18,26 @@ pub struct UdpSocket {
 }
 
 impl UdpSocket {
-    pub fn bind(addr: SocketAddr) -> Option<UdpSocket> {
+    pub fn bind(addr: SocketAddr) -> IoResult<UdpSocket> {
         LocalIo::maybe_raise(|io| {
             io.udp_bind(addr).map(|s| UdpSocket { obj: s })
         })
     }
 
-    pub fn recvfrom(&mut self, buf: &mut [u8]) -> Option<(uint, SocketAddr)> {
-        match self.obj.recvfrom(buf) {
-            Ok((nread, src)) => Some((nread, src)),
-            Err(ioerr) => {
-                // EOF is indicated by returning None
-                if ioerr.kind != EndOfFile {
-                    io_error::cond.raise(ioerr);
-                }
-                None
-            }
-        }
+    pub fn recvfrom(&mut self, buf: &mut [u8]) -> IoResult<(uint, SocketAddr)> {
+        self.obj.recvfrom(buf)
     }
 
-    pub fn sendto(&mut self, buf: &[u8], dst: SocketAddr) {
-        match self.obj.sendto(buf, dst) {
-            Ok(_) => (),
-            Err(ioerr) => io_error::cond.raise(ioerr),
-        }
+    pub fn sendto(&mut self, buf: &[u8], dst: SocketAddr) -> IoResult<()> {
+        self.obj.sendto(buf, dst)
     }
 
     pub fn connect(self, other: SocketAddr) -> UdpStream {
         UdpStream { socket: self, connectedTo: other }
     }
 
-    pub fn socket_name(&mut self) -> Option<SocketAddr> {
-        match self.obj.socket_name() {
-            Ok(sn) => Some(sn),
-            Err(ioerr) => {
-                debug!("failed to get socket name: {:?}", ioerr);
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    pub fn socket_name(&mut self) -> IoResult<SocketAddr> {
+        self.obj.socket_name()
     }
 }
 
@@ -76,21 +55,21 @@ impl UdpStream {
 }
 
 impl Reader for UdpStream {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
         let peer = self.connectedTo;
         self.as_socket(|sock| {
             match sock.recvfrom(buf) {
-                Some((_nread, src)) if src != peer => Some(0),
-                Some((nread, _src)) => Some(nread),
-                None => None,
+                Ok((_nread, src)) if src != peer => Ok(0),
+                Ok((nread, _src)) => Ok(nread),
+                Err(e) => Err(e),
             }
         })
     }
 }
 
 impl Writer for UdpStream {
-    fn write(&mut self, buf: &[u8]) {
-        self.as_socket(|sock| sock.sendto(buf, self.connectedTo));
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
+        self.as_socket(|sock| sock.sendto(buf, self.connectedTo))
     }
 }
 
@@ -101,16 +80,11 @@ mod test {
 
     // FIXME #11530 this fails on android because tests are run as root
     iotest!(fn bind_error() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert_eq!(e.kind, PermissionDenied);
-            called = true;
-        }).inside(|| {
-            let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
-            let socket = UdpSocket::bind(addr);
-            assert!(socket.is_none());
-        });
-        assert!(called);
+        let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
+        match UdpSocket::bind(addr) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, PermissionDenied),
+        }
     } #[ignore(cfg(windows))] #[ignore(cfg(target_os = "android"))])
 
     iotest!(fn socket_smoke_test_ip4() {
@@ -121,29 +95,29 @@ mod test {
 
         spawn(proc() {
             match UdpSocket::bind(client_ip) {
-                Some(ref mut client) => {
+                Ok(ref mut client) => {
                     port.recv();
-                    client.sendto([99], server_ip)
+                    client.sendto([99], server_ip).unwrap()
                 }
-                None => fail!()
+                Err(..) => fail!()
             }
             chan2.send(());
         });
 
         match UdpSocket::bind(server_ip) {
-            Some(ref mut server) => {
+            Ok(ref mut server) => {
                 chan.send(());
                 let mut buf = [0];
                 match server.recvfrom(buf) {
-                    Some((nread, src)) => {
+                    Ok((nread, src)) => {
                         assert_eq!(nread, 1);
                         assert_eq!(buf[0], 99);
                         assert_eq!(src, client_ip);
                     }
-                    None => fail!()
+                    Err(..) => fail!()
                 }
             }
-            None => fail!()
+            Err(..) => fail!()
         }
         port2.recv();
     })
@@ -155,28 +129,28 @@ mod test {
 
         spawn(proc() {
             match UdpSocket::bind(client_ip) {
-                Some(ref mut client) => {
+                Ok(ref mut client) => {
                     port.recv();
-                    client.sendto([99], server_ip)
+                    client.sendto([99], server_ip).unwrap()
                 }
-                None => fail!()
+                Err(..) => fail!()
             }
         });
 
         match UdpSocket::bind(server_ip) {
-            Some(ref mut server) => {
+            Ok(ref mut server) => {
                 chan.send(());
                 let mut buf = [0];
                 match server.recvfrom(buf) {
-                    Some((nread, src)) => {
+                    Ok((nread, src)) => {
                         assert_eq!(nread, 1);
                         assert_eq!(buf[0], 99);
                         assert_eq!(src, client_ip);
                     }
-                    None => fail!()
+                    Err(..) => fail!()
                 }
             }
-            None => fail!()
+            Err(..) => fail!()
         }
     })
 
@@ -188,32 +162,32 @@ mod test {
 
         spawn(proc() {
             match UdpSocket::bind(client_ip) {
-                Some(client) => {
+                Ok(client) => {
                     let client = ~client;
                     let mut stream = client.connect(server_ip);
                     port.recv();
-                    stream.write([99]);
+                    stream.write([99]).unwrap();
                 }
-                None => fail!()
+                Err(..) => fail!()
             }
             chan2.send(());
         });
 
         match UdpSocket::bind(server_ip) {
-            Some(server) => {
+            Ok(server) => {
                 let server = ~server;
                 let mut stream = server.connect(client_ip);
                 chan.send(());
                 let mut buf = [0];
                 match stream.read(buf) {
-                    Some(nread) => {
+                    Ok(nread) => {
                         assert_eq!(nread, 1);
                         assert_eq!(buf[0], 99);
                     }
-                    None => fail!()
+                    Err(..) => fail!()
                 }
             }
-            None => fail!()
+            Err(..) => fail!()
         }
         port2.recv();
     })
@@ -226,32 +200,32 @@ mod test {
 
         spawn(proc() {
             match UdpSocket::bind(client_ip) {
-                Some(client) => {
+                Ok(client) => {
                     let client = ~client;
                     let mut stream = client.connect(server_ip);
                     port.recv();
-                    stream.write([99]);
+                    stream.write([99]).unwrap();
                 }
-                None => fail!()
+                Err(..) => fail!()
             }
             chan2.send(());
         });
 
         match UdpSocket::bind(server_ip) {
-            Some(server) => {
+            Ok(server) => {
                 let server = ~server;
                 let mut stream = server.connect(client_ip);
                 chan.send(());
                 let mut buf = [0];
                 match stream.read(buf) {
-                    Some(nread) => {
+                    Ok(nread) => {
                         assert_eq!(nread, 1);
                         assert_eq!(buf[0], 99);
                     }
-                    None => fail!()
+                    Err(..) => fail!()
                 }
             }
-            None => fail!()
+            Err(..) => fail!()
         }
         port2.recv();
     })
@@ -259,13 +233,13 @@ mod test {
     pub fn socket_name(addr: SocketAddr) {
         let server = UdpSocket::bind(addr);
 
-        assert!(server.is_some());
+        assert!(server.is_ok());
         let mut server = server.unwrap();
 
         // Make sure socket_name gives
         // us the socket we binded to.
         let so_name = server.socket_name();
-        assert!(so_name.is_some());
+        assert!(so_name.is_ok());
         assert_eq!(addr, so_name.unwrap());
     }
 

src/libstd/io/net/unix.rs

@@ -28,7 +28,7 @@ use c_str::ToCStr;
 use rt::rtio::{IoFactory, LocalIo, RtioUnixListener};
 use rt::rtio::{RtioUnixAcceptor, RtioPipe};
 use io::pipe::PipeStream;
-use io::{io_error, Listener, Acceptor, Reader, Writer};
+use io::{Listener, Acceptor, Reader, Writer, IoResult};
 
 /// A stream which communicates over a named pipe.
 pub struct UnixStream {
@@ -45,20 +45,17 @@ impl UnixStream {
     ///
     /// The returned stream will be closed when the object falls out of scope.
     ///
-    /// # Failure
-    ///
-    /// This function will raise on the `io_error` condition if the connection
-    /// could not be made.
-    ///
     /// # Example
     ///
-    ///     use std::io::net::unix::UnixStream;
+    /// ```rust
+    /// # #[allow(unused_must_use)];
+    /// use std::io::net::unix::UnixStream;
     ///
-    ///     let server = Path("path/to/my/socket");
-    ///     let mut stream = UnixStream::connect(&server);
-    ///     stream.write([1, 2, 3]);
-    ///
-    pub fn connect<P: ToCStr>(path: &P) -> Option<UnixStream> {
+    /// let server = Path::new("path/to/my/socket");
+    /// let mut stream = UnixStream::connect(&server);
+    /// stream.write([1, 2, 3]);
+    /// ```
+    pub fn connect<P: ToCStr>(path: &P) -> IoResult<UnixStream> {
         LocalIo::maybe_raise(|io| {
             io.unix_connect(&path.to_c_str()).map(UnixStream::new)
         })
@@ -66,11 +63,11 @@ impl UnixStream {
 }
 
 impl Reader for UnixStream {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.obj.read(buf) }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> { self.obj.read(buf) }
 }
 
 impl Writer for UnixStream {
-    fn write(&mut self, buf: &[u8]) { self.obj.write(buf) }
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.obj.write(buf) }
 }
 
 pub struct UnixListener {
@@ -84,23 +81,20 @@ impl UnixListener {
     ///
     /// This listener will be closed when it falls out of scope.
     ///
-    /// # Failure
-    ///
-    /// This function will raise on the `io_error` condition if the specified
-    /// path could not be bound.
-    ///
     /// # Example
     ///
-    ///     use std::io::net::unix::UnixListener;
+    /// ```
+    /// use std::io::net::unix::UnixListener;
+    /// use std::io::Listener;
     ///
-    ///     let server = Path("path/to/my/socket");
-    ///     let mut stream = UnixListener::bind(&server);
-    ///     for client in stream.incoming() {
-    ///         let mut client = client;
-    ///         client.write([1, 2, 3, 4]);
-    ///     }
-    ///
-    pub fn bind<P: ToCStr>(path: &P) -> Option<UnixListener> {
+    /// let server = Path::new("path/to/my/socket");
+    /// let mut stream = UnixListener::bind(&server);
+    /// for client in stream.incoming() {
+    ///     let mut client = client;
+    ///     client.write([1, 2, 3, 4]);
+    /// }
+    /// ```
+    pub fn bind<P: ToCStr>(path: &P) -> IoResult<UnixListener> {
         LocalIo::maybe_raise(|io| {
             io.unix_bind(&path.to_c_str()).map(|s| UnixListener { obj: s })
         })
@@ -108,14 +102,8 @@ impl UnixListener {
 }
 
 impl Listener<UnixStream, UnixAcceptor> for UnixListener {
-    fn listen(self) -> Option<UnixAcceptor> {
-        match self.obj.listen() {
-            Ok(acceptor) => Some(UnixAcceptor { obj: acceptor }),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    fn listen(self) -> IoResult<UnixAcceptor> {
+        self.obj.listen().map(|obj| UnixAcceptor { obj: obj })
     }
 }
 
@@ -124,14 +112,8 @@ pub struct UnixAcceptor {
 }
 
 impl Acceptor<UnixStream> for UnixAcceptor {
-    fn accept(&mut self) -> Option<UnixStream> {
-        match self.obj.accept() {
-            Ok(s) => Some(UnixStream::new(s)),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    fn accept(&mut self) -> IoResult<UnixStream> {
+        self.obj.accept().map(UnixStream::new)
     }
 }
 
@@ -159,39 +141,29 @@ mod tests {
 
     #[test]
     fn bind_error() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert!(e.kind == PermissionDenied);
-            called = true;
-        }).inside(|| {
-            let listener = UnixListener::bind(&("path/to/nowhere"));
-            assert!(listener.is_none());
-        });
-        assert!(called);
+        match UnixListener::bind(&("path/to/nowhere")) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, PermissionDenied),
+        }
     }
 
     #[test]
     fn connect_error() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert_eq!(e.kind,
-                       if cfg!(windows) {OtherIoError} else {FileNotFound});
-            called = true;
-        }).inside(|| {
-            let stream = UnixStream::connect(&("path/to/nowhere"));
-            assert!(stream.is_none());
-        });
-        assert!(called);
+        match UnixStream::connect(&("path/to/nowhere")) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind,
+                        if cfg!(windows) {OtherIoError} else {FileNotFound})
+        }
     }
 
     #[test]
     fn smoke() {
         smalltest(proc(mut server) {
             let mut buf = [0];
-            server.read(buf);
+            server.read(buf).unwrap();
             assert!(buf[0] == 99);
         }, proc(mut client) {
-            client.write([99]);
+            client.write([99]).unwrap();
         })
     }
 
@@ -199,8 +171,8 @@ mod tests {
     fn read_eof() {
         smalltest(proc(mut server) {
             let mut buf = [0];
-            assert!(server.read(buf).is_none());
-            assert!(server.read(buf).is_none());
+            assert!(server.read(buf).is_err());
+            assert!(server.read(buf).is_err());
         }, proc(_client) {
             // drop the client
         })
@@ -210,15 +182,15 @@ mod tests {
     fn write_begone() {
         smalltest(proc(mut server) {
             let buf = [0];
-            let mut stop = false;
-            while !stop{
-                io_error::cond.trap(|e| {
-                    assert!(e.kind == BrokenPipe || e.kind == NotConnected,
-                            "unknown error {:?}", e);
-                    stop = true;
-                }).inside(|| {
-                    server.write(buf);
-                })
+            loop {
+                match server.write(buf) {
+                    Ok(..) => {}
+                    Err(e) => {
+                        assert!(e.kind == BrokenPipe || e.kind == NotConnected,
+                                "unknown error {:?}", e);
+                        break;
+                    }
+                }
             }
         }, proc(_client) {
             // drop the client
@@ -236,7 +208,7 @@ mod tests {
             port.recv();
             for _ in range(0, times) {
                 let mut stream = UnixStream::connect(&path2);
-                stream.write([100]);
+                stream.write([100]).unwrap();
             }
         });
 
@@ -245,7 +217,7 @@ mod tests {
         for _ in range(0, times) {
             let mut client = acceptor.accept();
             let mut buf = [0];
-            client.read(buf);
+            client.read(buf).unwrap();
             assert_eq!(buf[0], 100);
         }
     }

src/libstd/io/option.rs

@@ -1,154 +0,0 @@
-// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-//! Implementations of I/O traits for the Option type
-//!
-//! I/O constructors return option types to allow errors to be handled.
-//! These implementations allow e.g. `Option<File>` to be used
-//! as a `Reader` without unwrapping the option first.
-
-use option::*;
-use super::{Reader, Writer, Listener, Acceptor, Seek, SeekStyle};
-use super::{standard_error, PreviousIoError, io_error, IoError};
-
-fn prev_io_error() -> IoError {
-    standard_error(PreviousIoError)
-}
-
-impl<W: Writer> Writer for Option<W> {
-    fn write(&mut self, buf: &[u8]) {
-        match *self {
-            Some(ref mut writer) => writer.write(buf),
-            None => io_error::cond.raise(prev_io_error())
-        }
-    }
-
-    fn flush(&mut self) {
-        match *self {
-            Some(ref mut writer) => writer.flush(),
-            None => io_error::cond.raise(prev_io_error())
-        }
-    }
-}
-
-impl<R: Reader> Reader for Option<R> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        match *self {
-            Some(ref mut reader) => reader.read(buf),
-            None => {
-                io_error::cond.raise(prev_io_error());
-                None
-            }
-        }
-    }
-}
-
-impl<S: Seek> Seek for Option<S> {
-    fn tell(&self) -> u64 {
-        match *self {
-            Some(ref seeker) => seeker.tell(),
-            None => {
-                io_error::cond.raise(prev_io_error());
-                0
-            }
-        }
-    }
-    fn seek(&mut self, pos: i64, style: SeekStyle) {
-        match *self {
-            Some(ref mut seeker) => seeker.seek(pos, style),
-            None => io_error::cond.raise(prev_io_error())
-        }
-    }
-}
-
-impl<T, A: Acceptor<T>, L: Listener<T, A>> Listener<T, A> for Option<L> {
-    fn listen(self) -> Option<A> {
-        match self {
-            Some(listener) => listener.listen(),
-            None => {
-                io_error::cond.raise(prev_io_error());
-                None
-            }
-        }
-    }
-}
-
-impl<T, A: Acceptor<T>> Acceptor<T> for Option<A> {
-    fn accept(&mut self) -> Option<T> {
-        match *self {
-            Some(ref mut acceptor) => acceptor.accept(),
-            None => {
-                io_error::cond.raise(prev_io_error());
-                None
-            }
-        }
-    }
-}
-
-#[cfg(test)]
-mod test {
-    use prelude::*;
-    use super::super::mem::*;
-    use super::super::{PreviousIoError, io_error};
-
-    #[test]
-    fn test_option_writer() {
-        let mut writer: Option<MemWriter> = Some(MemWriter::new());
-        writer.write([0, 1, 2]);
-        writer.flush();
-        assert_eq!(writer.unwrap().unwrap(), ~[0, 1, 2]);
-    }
-
-    #[test]
-    fn test_option_writer_error() {
-        let mut writer: Option<MemWriter> = None;
-
-        let mut called = false;
-        io_error::cond.trap(|err| {
-            assert_eq!(err.kind, PreviousIoError);
-            called = true;
-        }).inside(|| {
-            writer.write([0, 0, 0]);
-        });
-        assert!(called);
-
-        let mut called = false;
-        io_error::cond.trap(|err| {
-            assert_eq!(err.kind, PreviousIoError);
-            called = true;
-        }).inside(|| {
-            writer.flush();
-        });
-        assert!(called);
-    }
-
-    #[test]
-    fn test_option_reader() {
-        let mut reader: Option<MemReader> = Some(MemReader::new(~[0, 1, 2, 3]));
-        let mut buf = [0, 0];
-        reader.read(buf);
-        assert_eq!(buf, [0, 1]);
-    }
-
-    #[test]
-    fn test_option_reader_error() {
-        let mut reader: Option<MemReader> = None;
-        let mut buf = [];
-
-        let mut called = false;
-        io_error::cond.trap(|err| {
-            assert_eq!(err.kind, PreviousIoError);
-            called = true;
-        }).inside(|| {
-            reader.read(buf);
-        });
-        assert!(called);
-    }
-}

src/libstd/io/pipe.rs

@@ -14,7 +14,7 @@
 //! enough so that pipes can be created to child processes.
 
 use prelude::*;
-use io::{io_error, EndOfFile};
+use io::IoResult;
 use libc;
 use rt::rtio::{RtioPipe, LocalIo};
 
@@ -32,17 +32,15 @@ impl PipeStream {
     ///
     /// # Example
     ///
-    ///     use std::libc;
-    ///     use std::io::pipe;
+    /// ```rust
+    /// # #[allow(unused_must_use)];
+    /// use std::libc;
+    /// use std::io::pipe::PipeStream;
     ///
-    ///     let mut pipe = PipeStream::open(libc::STDERR_FILENO);
-    ///     pipe.write(bytes!("Hello, stderr!"));
-    ///
-    /// # Failure
-    ///
-    /// If the pipe cannot be created, an error will be raised on the
-    /// `io_error` condition.
-    pub fn open(fd: libc::c_int) -> Option<PipeStream> {
+    /// let mut pipe = PipeStream::open(libc::STDERR_FILENO);
+    /// pipe.write(bytes!("Hello, stderr!"));
+    /// ```
+    pub fn open(fd: libc::c_int) -> IoResult<PipeStream> {
         LocalIo::maybe_raise(|io| {
             io.pipe_open(fd).map(|obj| PipeStream { obj: obj })
         })
@@ -54,29 +52,11 @@ impl PipeStream {
 }
 
 impl Reader for PipeStream {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        match self.obj.read(buf) {
-            Ok(read) => Some(read),
-            Err(ioerr) => {
-                // EOF is indicated by returning None
-                if ioerr.kind != EndOfFile {
-                    io_error::cond.raise(ioerr);
-                }
-                return None;
-            }
-        }
-    }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> { self.obj.read(buf) }
 }
 
 impl Writer for PipeStream {
-    fn write(&mut self, buf: &[u8]) {
-        match self.obj.write(buf) {
-            Ok(_) => (),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-            }
-        }
-    }
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.obj.write(buf) }
 }
 
 #[cfg(test)]
@@ -91,12 +71,12 @@ mod test {
         let (p, c) = Chan::new();
         spawn(proc() {
             let mut out = out;
-            out.write([10]);
+            out.write([10]).unwrap();
             p.recv(); // don't close the pipe until the other read has finished
         });
 
         let mut buf = [0, ..10];
-        input.read(buf);
+        input.read(buf).unwrap();
         c.send(());
     })
 }

src/libstd/io/process.rs

@@ -14,7 +14,7 @@ use prelude::*;
 
 use libc;
 use io;
-use io::io_error;
+use io::IoResult;
 use rt::rtio::{RtioProcess, IoFactory, LocalIo};
 
 use fmt;
@@ -93,7 +93,7 @@ pub enum ProcessExit {
 
 impl fmt::Show for ProcessExit {
     /// Format a ProcessExit enum, to nicely present the information.
-    fn fmt(obj: &ProcessExit, f: &mut fmt::Formatter) {
+    fn fmt(obj: &ProcessExit, f: &mut fmt::Formatter) -> fmt::Result {
         match *obj {
             ExitStatus(code) =>  write!(f.buf, "exit code: {}", code),
             ExitSignal(code) =>  write!(f.buf, "signal: {}", code),
@@ -118,7 +118,7 @@ impl ProcessExit {
 impl Process {
     /// Creates a new pipe initialized, but not bound to any particular
     /// source/destination
-    pub fn new(config: ProcessConfig) -> Option<Process> {
+    pub fn new(config: ProcessConfig) -> IoResult<Process> {
         let mut config = Some(config);
         LocalIo::maybe_raise(|io| {
             io.spawn(config.take_unwrap()).map(|(p, io)| {
@@ -141,14 +141,9 @@ impl Process {
     /// Note that this is purely a wrapper around libuv's `uv_process_kill`
     /// function.
     ///
-    /// If the signal delivery fails, then the `io_error` condition is raised on
-    pub fn signal(&mut self, signal: int) {
-        match self.handle.kill(signal) {
-            Ok(()) => {}
-            Err(err) => {
-                io_error::cond.raise(err)
-            }
-        }
+    /// If the signal delivery fails, the corresponding error is returned.
+    pub fn signal(&mut self, signal: int) -> IoResult<()> {
+        self.handle.kill(signal)
     }
 
     /// Wait for the child to exit completely, returning the status that it
@@ -176,7 +171,6 @@ impl Drop for Process {
 mod tests {
     use io::process::{ProcessConfig, Process};
     use prelude::*;
-    use str;
 
     // FIXME(#10380)
     #[cfg(unix, not(target_os="android"))]
@@ -190,7 +184,7 @@ mod tests {
             io: io,
         };
         let p = Process::new(args);
-        assert!(p.is_some());
+        assert!(p.is_ok());
         let mut p = p.unwrap();
         assert!(p.wait().success());
     })
@@ -206,7 +200,7 @@ mod tests {
             cwd: None,
             io: io,
         };
-        match io::result(|| Process::new(args)) {
+        match Process::new(args) {
             Ok(..) => fail!(),
             Err(..) => {}
         }
@@ -224,7 +218,7 @@ mod tests {
             io: io,
         };
         let p = Process::new(args);
-        assert!(p.is_some());
+        assert!(p.is_ok());
         let mut p = p.unwrap();
         assert!(p.wait().matches_exit_status(1));
     })
@@ -240,7 +234,7 @@ mod tests {
             io: io,
         };
         let p = Process::new(args);
-        assert!(p.is_some());
+        assert!(p.is_ok());
         let mut p = p.unwrap();
         match p.wait() {
             process::ExitSignal(1) => {},
@@ -249,20 +243,12 @@ mod tests {
     })
 
     pub fn read_all(input: &mut Reader) -> ~str {
-        let mut ret = ~"";
-        let mut buf = [0, ..1024];
-        loop {
-            match input.read(buf) {
-                None => { break }
-                Some(n) => { ret.push_str(str::from_utf8(buf.slice_to(n)).unwrap()); }
-            }
-        }
-        return ret;
+        input.read_to_str().unwrap()
     }
 
     pub fn run_output(args: ProcessConfig) -> ~str {
         let p = Process::new(args);
-        assert!(p.is_some());
+        assert!(p.is_ok());
         let mut p = p.unwrap();
         assert!(p.io[0].is_none());
         assert!(p.io[1].is_some());
@@ -312,8 +298,8 @@ mod tests {
             cwd: None,
             io: io,
         };
-        let mut p = Process::new(args).expect("didn't create a proces?!");
-        p.io[0].get_mut_ref().write("foobar".as_bytes());
+        let mut p = Process::new(args).unwrap();
+        p.io[0].get_mut_ref().write("foobar".as_bytes()).unwrap();
         p.io[0] = None; // close stdin;
         let out = read_all(p.io[1].get_mut_ref() as &mut Reader);
         assert!(p.wait().success());

src/libstd/io/result.rs

@@ -0,0 +1,128 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Implementations of I/O traits for the IoResult type
+//!
+//! I/O constructors return option types to allow errors to be handled.
+//! These implementations allow e.g. `IoResult<File>` to be used
+//! as a `Reader` without unwrapping the result first.
+
+use clone::Clone;
+use result::{Ok, Err};
+use super::{Reader, Writer, Listener, Acceptor, Seek, SeekStyle, IoResult};
+
+impl<W: Writer> Writer for IoResult<W> {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
+        match *self {
+            Ok(ref mut writer) => writer.write(buf),
+            Err(ref e) => Err((*e).clone())
+        }
+    }
+
+    fn flush(&mut self) -> IoResult<()> {
+        match *self {
+            Ok(ref mut writer) => writer.flush(),
+            Err(ref e) => Err(e.clone()),
+        }
+    }
+}
+
+impl<R: Reader> Reader for IoResult<R> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
+        match *self {
+            Ok(ref mut reader) => reader.read(buf),
+            Err(ref e) => Err(e.clone()),
+        }
+    }
+}
+
+impl<S: Seek> Seek for IoResult<S> {
+    fn tell(&self) -> IoResult<u64> {
+        match *self {
+            Ok(ref seeker) => seeker.tell(),
+            Err(ref e) => Err(e.clone()),
+        }
+    }
+    fn seek(&mut self, pos: i64, style: SeekStyle) -> IoResult<()> {
+        match *self {
+            Ok(ref mut seeker) => seeker.seek(pos, style),
+            Err(ref e) => Err(e.clone())
+        }
+    }
+}
+
+impl<T, A: Acceptor<T>, L: Listener<T, A>> Listener<T, A> for IoResult<L> {
+    fn listen(self) -> IoResult<A> {
+        match self {
+            Ok(listener) => listener.listen(),
+            Err(e) => Err(e),
+        }
+    }
+}
+
+impl<T, A: Acceptor<T>> Acceptor<T> for IoResult<A> {
+    fn accept(&mut self) -> IoResult<T> {
+        match *self {
+            Ok(ref mut acceptor) => acceptor.accept(),
+            Err(ref e) => Err(e.clone()),
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use prelude::*;
+    use super::super::mem::*;
+    use io;
+
+    #[test]
+    fn test_option_writer() {
+        let mut writer: io::IoResult<MemWriter> = Ok(MemWriter::new());
+        writer.write([0, 1, 2]).unwrap();
+        writer.flush().unwrap();
+        assert_eq!(writer.unwrap().unwrap(), ~[0, 1, 2]);
+    }
+
+    #[test]
+    fn test_option_writer_error() {
+        let mut writer: io::IoResult<MemWriter> =
+            Err(io::standard_error(io::EndOfFile));
+
+        match writer.write([0, 0, 0]) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::EndOfFile),
+        }
+        match writer.flush() {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::EndOfFile),
+        }
+    }
+
+    #[test]
+    fn test_option_reader() {
+        let mut reader: io::IoResult<MemReader> =
+            Ok(MemReader::new(~[0, 1, 2, 3]));
+        let mut buf = [0, 0];
+        reader.read(buf).unwrap();
+        assert_eq!(buf, [0, 1]);
+    }
+
+    #[test]
+    fn test_option_reader_error() {
+        let mut reader: io::IoResult<MemReader> =
+            Err(io::standard_error(io::EndOfFile));
+        let mut buf = [];
+
+        match reader.read(buf) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::EndOfFile),
+        }
+    }
+}

src/libstd/io/signal.rs

@@ -20,10 +20,11 @@ definitions for a number of signals.
 */
 
 use clone::Clone;
+use result::{Ok, Err};
 use comm::{Port, SharedChan};
 use container::{Map, MutableMap};
 use hashmap;
-use option::{Some, None};
+use io;
 use rt::rtio::{IoFactory, LocalIo, RtioSignal};
 
 #[repr(int)]
@@ -112,23 +113,22 @@ impl Listener {
     /// a signal, and a later call to `recv` will return the signal that was
     /// received while no task was waiting on it.
     ///
-    /// # Failure
+    /// # Error
     ///
     /// If this function fails to register a signal handler, then an error will
-    /// be raised on the `io_error` condition and the function will return
-    /// false.
-    pub fn register(&mut self, signum: Signum) -> bool {
+    /// be returned.
+    pub fn register(&mut self, signum: Signum) -> io::IoResult<()> {
         if self.handles.contains_key(&signum) {
-            return true; // self is already listening to signum, so succeed
+            return Ok(()); // self is already listening to signum, so succeed
         }
         match LocalIo::maybe_raise(|io| {
             io.signal(signum, self.chan.clone())
         }) {
-            Some(handle) => {
+            Ok(handle) => {
                 self.handles.insert(signum, handle);
-                true
+                Ok(())
             }
-            None => false
+            Err(e) => Err(e)
         }
     }
 
@@ -159,7 +159,7 @@ mod test {
     #[test] #[cfg(unix, not(target_os="android"))] // FIXME(#10378)
     fn test_io_signal_smoketest() {
         let mut signal = Listener::new();
-        signal.register(Interrupt);
+        signal.register(Interrupt).unwrap();
         sigint();
         timer::sleep(10);
         match signal.port.recv() {
@@ -172,8 +172,8 @@ mod test {
     fn test_io_signal_two_signal_one_signum() {
         let mut s1 = Listener::new();
         let mut s2 = Listener::new();
-        s1.register(Interrupt);
-        s2.register(Interrupt);
+        s1.register(Interrupt).unwrap();
+        s2.register(Interrupt).unwrap();
         sigint();
         timer::sleep(10);
         match s1.port.recv() {
@@ -190,8 +190,8 @@ mod test {
     fn test_io_signal_unregister() {
         let mut s1 = Listener::new();
         let mut s2 = Listener::new();
-        s1.register(Interrupt);
-        s2.register(Interrupt);
+        s1.register(Interrupt).unwrap();
+        s2.register(Interrupt).unwrap();
         s2.unregister(Interrupt);
         sigint();
         timer::sleep(10);
@@ -203,15 +203,14 @@ mod test {
     fn test_io_signal_invalid_signum() {
         use io;
         use super::User1;
+        use result::{Ok, Err};
         let mut s = Listener::new();
         let mut called = false;
-        io::io_error::cond.trap(|_| {
-            called = true;
-        }).inside(|| {
-            if s.register(User1) {
+        match s.register(User1) {
+            Ok(..) => {
                 fail!("Unexpected successful registry of signum {:?}", User1);
             }
-        });
-        assert!(called);
+            Err(..) => {}
+        }
     }
 }

src/libstd/io/stdio.rs

@@ -18,6 +18,7 @@ about the stream or terminal that it is attached to.
 # Example
 
 ```rust
+# #[allow(unused_must_use)];
 use std::io;
 
 let mut out = io::stdout();
@@ -28,7 +29,7 @@ out.write(bytes!("Hello, world!"));
 
 use container::Container;
 use fmt;
-use io::{Reader, Writer, io_error, IoError, OtherIoError,
+use io::{Reader, Writer, IoResult, IoError, OtherIoError,
          standard_error, EndOfFile, LineBufferedWriter};
 use libc;
 use option::{Option, Some, None};
@@ -114,7 +115,8 @@ fn reset_helper(w: ~Writer,
     match f(t.get(), w) {
         Some(mut w) => {
             drop(t);
-            w.flush();
+            // FIXME: is failing right here?
+            w.flush().unwrap();
             Some(w)
         }
         None => None
@@ -155,9 +157,9 @@ pub fn set_stderr(stderr: ~Writer) -> Option<~Writer> {
 //          // io1 aliases io2
 //      })
 //  })
-fn with_task_stdout(f: |&mut Writer|) {
+fn with_task_stdout(f: |&mut Writer| -> IoResult<()> ) {
     let task: Option<~Task> = Local::try_take();
-    match task {
+    let result = match task {
         Some(mut task) => {
             // Printing may run arbitrary code, so ensure that the task is in
             // TLS to allow all std services. Note that this means a print while
@@ -169,7 +171,7 @@ fn with_task_stdout(f: |&mut Writer|) {
             if my_stdout.is_none() {
                 my_stdout = Some(~LineBufferedWriter::new(stdout()) as ~Writer);
             }
-            f(*my_stdout.get_mut_ref());
+            let ret = f(*my_stdout.get_mut_ref());
 
             // Note that we need to be careful when putting the stdout handle
             // back into the task. If the handle was set to `Some` while
@@ -184,22 +186,29 @@ fn with_task_stdout(f: |&mut Writer|) {
             let prev = util::replace(&mut t.get().stdout, my_stdout);
             drop(t);
             drop(prev);
+            ret
         }
 
         None => {
             struct Stdout;
             impl Writer for Stdout {
-                fn write(&mut self, data: &[u8]) {
+                fn write(&mut self, data: &[u8]) -> IoResult<()> {
                     unsafe {
                         libc::write(libc::STDOUT_FILENO,
                                     data.as_ptr() as *libc::c_void,
                                     data.len() as libc::size_t);
                     }
+                    Ok(()) // just ignore the results
                 }
             }
             let mut io = Stdout;
-            f(&mut io as &mut Writer);
+            f(&mut io as &mut Writer)
         }
+    };
+
+    match result {
+        Ok(()) => {}
+        Err(e) => fail!("failed printing to stdout: {}", e),
     }
 }
 
@@ -226,8 +235,7 @@ pub fn print(s: &str) {
 /// `\n` character is printed to the console after the string.
 pub fn println(s: &str) {
     with_task_stdout(|io| {
-        io.write(s.as_bytes());
-        io.write(['\n' as u8]);
+        io.write(s.as_bytes()).and_then(|()| io.write(['\n' as u8]))
     })
 }
 
@@ -249,7 +257,7 @@ pub struct StdReader {
 }
 
 impl Reader for StdReader {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
         let ret = match self.inner {
             TTY(ref mut tty) => tty.read(buf),
             File(ref mut file) => file.read(buf).map(|i| i as uint),
@@ -260,15 +268,8 @@ impl Reader for StdReader {
             // return an actual EOF error, but apparently for stdin it's a
             // little different. Hence, here we convert a 0 length read to an
             // end-of-file indicator so the caller knows to stop reading.
-            Ok(0) => {
-                io_error::cond.raise(standard_error(EndOfFile));
-                None
-            }
-            Ok(amt) => Some(amt),
-            Err(e) => {
-                io_error::cond.raise(e);
-                None
-            }
+            Ok(0) => { Err(standard_error(EndOfFile)) }
+            ret @ Ok(..) | ret @ Err(..) => ret,
         }
     }
 }
@@ -283,30 +284,21 @@ impl StdWriter {
     /// when the writer is attached to something like a terminal, this is used
     /// to fetch the dimensions of the terminal.
     ///
-    /// If successful, returns Some((width, height)).
+    /// If successful, returns `Ok((width, height))`.
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// This function will raise on the `io_error` condition if an error
-    /// happens.
-    pub fn winsize(&mut self) -> Option<(int, int)> {
+    /// This function will return an error if the output stream is not actually
+    /// connected to a TTY instance, or if querying the TTY instance fails.
+    pub fn winsize(&mut self) -> IoResult<(int, int)> {
         match self.inner {
-            TTY(ref mut tty) => {
-                match tty.get_winsize() {
-                    Ok(p) => Some(p),
-                    Err(e) => {
-                        io_error::cond.raise(e);
-                        None
-                    }
-                }
-            }
+            TTY(ref mut tty) => tty.get_winsize(),
             File(..) => {
-                io_error::cond.raise(IoError {
+                Err(IoError {
                     kind: OtherIoError,
                     desc: "stream is not a tty",
                     detail: None,
-                });
-                None
+                })
             }
         }
     }
@@ -314,24 +306,19 @@ impl StdWriter {
     /// Controls whether this output stream is a "raw stream" or simply a normal
     /// stream.
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// This function will raise on the `io_error` condition if an error
-    /// happens.
-    pub fn set_raw(&mut self, raw: bool) {
+    /// This function will return an error if the output stream is not actually
+    /// connected to a TTY instance, or if querying the TTY instance fails.
+    pub fn set_raw(&mut self, raw: bool) -> IoResult<()> {
         match self.inner {
-            TTY(ref mut tty) => {
-                match tty.set_raw(raw) {
-                    Ok(()) => {},
-                    Err(e) => io_error::cond.raise(e),
-                }
-            }
+            TTY(ref mut tty) => tty.set_raw(raw),
             File(..) => {
-                io_error::cond.raise(IoError {
+                Err(IoError {
                     kind: OtherIoError,
                     desc: "stream is not a tty",
                     detail: None,
-                });
+                })
             }
         }
     }
@@ -346,14 +333,10 @@ impl StdWriter {
 }
 
 impl Writer for StdWriter {
-    fn write(&mut self, buf: &[u8]) {
-        let ret = match self.inner {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
+        match self.inner {
             TTY(ref mut tty) => tty.write(buf),
             File(ref mut file) => file.write(buf),
-        };
-        match ret {
-            Ok(()) => {}
-            Err(e) => io_error::cond.raise(e)
         }
     }
 }
@@ -376,7 +359,7 @@ mod tests {
             set_stdout(~w as ~Writer);
             println!("hello!");
         });
-        assert_eq!(r.read_to_str(), ~"hello!\n");
+        assert_eq!(r.read_to_str().unwrap(), ~"hello!\n");
     })
 
     iotest!(fn capture_stderr() {
@@ -388,7 +371,7 @@ mod tests {
             set_stderr(~w as ~Writer);
             fail!("my special message");
         });
-        let s = r.read_to_str();
+        let s = r.read_to_str().unwrap();
         assert!(s.contains("my special message"));
     })
 }

src/libstd/io/timer.rs

@@ -39,8 +39,8 @@ loop {
 */
 
 use comm::Port;
-use option::Option;
 use rt::rtio::{IoFactory, LocalIo, RtioTimer};
+use io::IoResult;
 
 pub struct Timer {
     priv obj: ~RtioTimer
@@ -48,7 +48,8 @@ pub struct Timer {
 
 /// Sleep the current task for `msecs` milliseconds.
 pub fn sleep(msecs: u64) {
-    let mut timer = Timer::new().expect("timer::sleep: could not create a Timer");
+    let timer = Timer::new();
+    let mut timer = timer.ok().expect("timer::sleep: could not create a Timer");
 
     timer.sleep(msecs)
 }
@@ -57,7 +58,7 @@ impl Timer {
     /// Creates a new timer which can be used to put the current task to sleep
     /// for a number of milliseconds, or to possibly create channels which will
     /// get notified after an amount of time has passed.
-    pub fn new() -> Option<Timer> {
+    pub fn new() -> IoResult<Timer> {
         LocalIo::maybe_raise(|io| io.timer_init().map(|t| Timer { obj: t }))
     }
 

src/libstd/io/util.rs

@@ -7,8 +7,10 @@
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
+
 use prelude::*;
 use cmp;
+use io;
 use vec::bytes::MutableByteVector;
 
 /// Wraps a `Reader`, limiting the number of bytes that can be read from it.
@@ -25,9 +27,9 @@ impl<'a, R: Reader> LimitReader<'a, R> {
 }
 
 impl<'a, R: Reader> Reader for LimitReader<'a, R> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
         if self.limit == 0 {
-            return None;
+            return Err(io::standard_error(io::EndOfFile));
         }
 
         let len = cmp::min(self.limit, buf.len());
@@ -43,7 +45,7 @@ pub struct NullWriter;
 
 impl Writer for NullWriter {
     #[inline]
-    fn write(&mut self, _buf: &[u8]) { }
+    fn write(&mut self, _buf: &[u8]) -> io::IoResult<()> { Ok(()) }
 }
 
 /// A `Reader` which returns an infinite stream of 0 bytes, like /dev/zero.
@@ -51,9 +53,9 @@ pub struct ZeroReader;
 
 impl Reader for ZeroReader {
     #[inline]
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
         buf.set_memory(0);
-        Some(buf.len())
+        Ok(buf.len())
     }
 }
 
@@ -62,8 +64,8 @@ pub struct NullReader;
 
 impl Reader for NullReader {
     #[inline]
-    fn read(&mut self, _buf: &mut [u8]) -> Option<uint> {
-        None
+    fn read(&mut self, _buf: &mut [u8]) -> io::IoResult<uint> {
+        Err(io::standard_error(io::EndOfFile))
     }
 }
 
@@ -81,17 +83,21 @@ impl MultiWriter {
 
 impl Writer for MultiWriter {
     #[inline]
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> io::IoResult<()> {
+        let mut ret = Ok(());
         for writer in self.writers.mut_iter() {
-            writer.write(buf);
+            ret = ret.and(writer.write(buf));
         }
+        return ret;
     }
 
     #[inline]
-    fn flush(&mut self) {
+    fn flush(&mut self) -> io::IoResult<()> {
+        let mut ret = Ok(());
         for writer in self.writers.mut_iter() {
-            writer.flush();
+            ret = ret.and(writer.flush());
         }
+        return ret;
     }
 }
 
@@ -111,20 +117,25 @@ impl<R: Reader, I: Iterator<R>> ChainedReader<I, R> {
 }
 
 impl<R: Reader, I: Iterator<R>> Reader for ChainedReader<I, R> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
         loop {
-            match self.cur_reader {
+            let err = match self.cur_reader {
                 Some(ref mut r) => {
                     match r.read(buf) {
-                        Some(len) => return Some(len),
-                        None => {}
+                        Ok(len) => return Ok(len),
+                        Err(ref e) if e.kind == io::EndOfFile => None,
+                        Err(e) => Some(e),
                     }
                 }
                 None => break
+            };
+            self.cur_reader = self.readers.next();
+            match err {
+                Some(e) => return Err(e),
+                None => {}
             }
-            self.cur_reader = self.readers.next()
         }
-        None
+        Err(io::standard_error(io::EndOfFile))
     }
 }
 
@@ -150,27 +161,29 @@ impl<R: Reader, W: Writer> TeeReader<R, W> {
 }
 
 impl<R: Reader, W: Writer> Reader for TeeReader<R, W> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        self.reader.read(buf).map(|len| {
-            self.writer.write(buf.slice_to(len));
-            len
+    fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
+        self.reader.read(buf).and_then(|len| {
+            self.writer.write(buf.slice_to(len)).map(|()| len)
         })
     }
 }
 
 /// Copies all data from a `Reader` to a `Writer`.
-pub fn copy<R: Reader, W: Writer>(r: &mut R, w: &mut W) {
+pub fn copy<R: Reader, W: Writer>(r: &mut R, w: &mut W) -> io::IoResult<()> {
     let mut buf = [0, ..super::DEFAULT_BUF_SIZE];
     loop {
-        match r.read(buf) {
-            Some(len) => w.write(buf.slice_to(len)),
-            None => break
-        }
+        let len = match r.read(buf) {
+            Ok(len) => len,
+            Err(ref e) if e.kind == io::EndOfFile => return Ok(()),
+            Err(e) => return Err(e),
+        };
+        if_ok!(w.write(buf.slice_to(len)));
     }
 }
 
 #[cfg(test)]
 mod test {
+    use io;
     use io::{MemReader, MemWriter};
     use super::*;
     use prelude::*;
@@ -180,7 +193,7 @@ mod test {
         let mut r = MemReader::new(~[0, 1, 2]);
         {
             let mut r = LimitReader::new(&mut r, 4);
-            assert_eq!(~[0, 1, 2], r.read_to_end());
+            assert_eq!(~[0, 1, 2], r.read_to_end().unwrap());
         }
     }
 
@@ -189,24 +202,24 @@ mod test {
         let mut r = MemReader::new(~[0, 1, 2]);
         {
             let mut r = LimitReader::new(&mut r, 2);
-            assert_eq!(~[0, 1], r.read_to_end());
+            assert_eq!(~[0, 1], r.read_to_end().unwrap());
         }
-        assert_eq!(~[2], r.read_to_end());
+        assert_eq!(~[2], r.read_to_end().unwrap());
     }
 
     #[test]
     fn test_null_writer() {
         let mut s = NullWriter;
         let buf = ~[0, 0, 0];
-        s.write(buf);
-        s.flush();
+        s.write(buf).unwrap();
+        s.flush().unwrap();
     }
 
     #[test]
     fn test_zero_reader() {
         let mut s = ZeroReader;
         let mut buf = ~[1, 2, 3];
-        assert_eq!(s.read(buf), Some(3));
+        assert_eq!(s.read(buf), Ok(3));
         assert_eq!(~[0, 0, 0], buf);
     }
 
@@ -214,7 +227,7 @@ mod test {
     fn test_null_reader() {
         let mut r = NullReader;
         let mut buf = ~[0];
-        assert_eq!(r.read(buf), None);
+        assert!(r.read(buf).is_err());
     }
 
     #[test]
@@ -224,21 +237,23 @@ mod test {
 
         struct TestWriter;
         impl Writer for TestWriter {
-            fn write(&mut self, _buf: &[u8]) {
+            fn write(&mut self, _buf: &[u8]) -> io::IoResult<()> {
                 unsafe { writes += 1 }
+                Ok(())
             }
 
-            fn flush(&mut self) {
+            fn flush(&mut self) -> io::IoResult<()> {
                 unsafe { flushes += 1 }
+                Ok(())
             }
         }
 
         let mut multi = MultiWriter::new(~[~TestWriter as ~Writer,
                                            ~TestWriter as ~Writer]);
-        multi.write([1, 2, 3]);
+        multi.write([1, 2, 3]).unwrap();
         assert_eq!(2, unsafe { writes });
         assert_eq!(0, unsafe { flushes });
-        multi.flush();
+        multi.flush().unwrap();
         assert_eq!(2, unsafe { writes });
         assert_eq!(2, unsafe { flushes });
     }
@@ -248,14 +263,14 @@ mod test {
         let rs = ~[MemReader::new(~[0, 1]), MemReader::new(~[]),
                    MemReader::new(~[2, 3])];
         let mut r = ChainedReader::new(rs.move_iter());
-        assert_eq!(~[0, 1, 2, 3], r.read_to_end());
+        assert_eq!(~[0, 1, 2, 3], r.read_to_end().unwrap());
     }
 
     #[test]
     fn test_tee_reader() {
         let mut r = TeeReader::new(MemReader::new(~[0, 1, 2]),
                                    MemWriter::new());
-        assert_eq!(~[0, 1, 2], r.read_to_end());
+        assert_eq!(~[0, 1, 2], r.read_to_end().unwrap());
         let (_, w) = r.unwrap();
         assert_eq!(~[0, 1, 2], w.unwrap());
     }
@@ -264,7 +279,7 @@ mod test {
     fn test_copy() {
         let mut r = MemReader::new(~[0, 1, 2, 3, 4]);
         let mut w = MemWriter::new();
-        copy(&mut r, &mut w);
+        copy(&mut r, &mut w).unwrap();
         assert_eq!(~[0, 1, 2, 3, 4], w.unwrap());
     }
 }

src/libstd/logging.rs

@@ -102,6 +102,7 @@ use io::Writer;
 use ops::Drop;
 use option::{Some, None, Option};
 use prelude::drop;
+use result::{Ok, Err};
 use rt::local::Local;
 use rt::task::Task;
 use util;
@@ -131,13 +132,19 @@ struct DefaultLogger {
 impl Logger for DefaultLogger {
     // by default, just ignore the level
     fn log(&mut self, _level: u32, args: &fmt::Arguments) {
-        fmt::writeln(&mut self.handle, args);
+        match fmt::writeln(&mut self.handle, args) {
+            Err(e) => fail!("failed to log: {}", e),
+            Ok(()) => {}
+        }
     }
 }
 
 impl Drop for DefaultLogger {
     fn drop(&mut self) {
-        self.handle.flush();
+        match self.handle.flush() {
+            Err(e) => fail!("failed to flush a logger: {}", e),
+            Ok(()) => {}
+        }
     }
 }
 

src/libstd/macros.rs

@@ -197,3 +197,8 @@ macro_rules! local_data_key (
         pub static $name: ::std::local_data::Key<$ty> = &::std::local_data::Key;
     )
 )
+
+#[macro_export]
+macro_rules! if_ok (
+    ($e:expr) => (match $e { Ok(e) => e, Err(e) => return Err(e) })
+)

src/libstd/option.rs

@@ -382,7 +382,7 @@ impl<T: Default> Option<T> {
 
 impl<T: fmt::Show> fmt::Show for Option<T> {
     #[inline]
-    fn fmt(s: &Option<T>, f: &mut fmt::Formatter) {
+    fn fmt(s: &Option<T>, f: &mut fmt::Formatter) -> fmt::Result {
         match *s {
             Some(ref t) => write!(f.buf, "Some({})", *t),
             None        => write!(f.buf, "None")

src/libstd/os.rs

@@ -372,9 +372,9 @@ pub fn self_exe_name() -> Option<Path> {
     fn load_self() -> Option<~[u8]> {
         use std::io;
 
-        match io::result(|| io::fs::readlink(&Path::new("/proc/self/exe"))) {
-            Ok(Some(path)) => Some(path.as_vec().to_owned()),
-            Ok(None) | Err(..) => None
+        match io::fs::readlink(&Path::new("/proc/self/exe")) {
+            Ok(path) => Some(path.as_vec().to_owned()),
+            Err(..) => None
         }
     }
 
@@ -929,7 +929,7 @@ pub enum MapError {
 }
 
 impl fmt::Show for MapError {
-    fn fmt(val: &MapError, out: &mut fmt::Formatter) {
+    fn fmt(val: &MapError, out: &mut fmt::Formatter) -> fmt::Result {
         let str = match *val {
             ErrFdNotAvail => "fd not available for reading or writing",
             ErrInvalidFd => "Invalid fd",
@@ -944,23 +944,19 @@ impl fmt::Show for MapError {
             ErrAlreadyExists => "File mapping for specified file already exists",
             ErrZeroLength => "Zero-length mapping not allowed",
             ErrUnknown(code) => {
-                write!(out.buf, "Unknown error = {}", code);
-                return
+                return write!(out.buf, "Unknown error = {}", code)
             },
             ErrVirtualAlloc(code) => {
-                write!(out.buf, "VirtualAlloc failure = {}", code);
-                return
+                return write!(out.buf, "VirtualAlloc failure = {}", code)
             },
             ErrCreateFileMappingW(code) => {
-                format!("CreateFileMappingW failure = {}", code);
-                return
+                return write!(out.buf, "CreateFileMappingW failure = {}", code)
             },
             ErrMapViewOfFile(code) => {
-                write!(out.buf, "MapViewOfFile failure = {}", code);
-                return
+                return write!(out.buf, "MapViewOfFile failure = {}", code)
             }
         };
-        write!(out.buf, "{}", str);
+        write!(out.buf, "{}", str)
     }
 }
 
@@ -1496,7 +1492,6 @@ mod tests {
         use result::{Ok, Err};
         use os::*;
         use libc::*;
-        use io;
         use io::fs;
 
         #[cfg(unix)]
@@ -1540,9 +1535,9 @@ mod tests {
             assert!(*chunk.data == 0xbe);
             close(fd);
         }
+        drop(chunk);
 
-        let _guard = io::ignore_io_error();
-        fs::unlink(&path);
+        fs::unlink(&path).unwrap();
     }
 
     // More recursive_mkdir tests are in extra::tempfile

src/libstd/path/mod.rs

@@ -533,7 +533,7 @@ pub struct Display<'a, P> {
 }
 
 impl<'a, P: GenericPath> fmt::Show for Display<'a, P> {
-    fn fmt(d: &Display<P>, f: &mut fmt::Formatter) {
+    fn fmt(d: &Display<P>, f: &mut fmt::Formatter) -> fmt::Result {
         d.with_str(|s| f.pad(s))
     }
 }

src/libstd/rand/os.rs

@@ -62,7 +62,7 @@ impl OSRng {
     pub fn new() -> OSRng {
         use path::Path;
         let reader = File::open(&Path::new("/dev/urandom"));
-        let reader = reader.expect("Error opening /dev/urandom");
+        let reader = reader.ok().expect("Error opening /dev/urandom");
         let reader_rng = ReaderRng::new(reader);
 
         OSRng { inner: reader_rng }

src/libstd/rand/reader.rs

@@ -11,7 +11,7 @@
 //! A wrapper around any Reader to treat it as an RNG.
 
 use container::Container;
-use option::{Some, None};
+use result::{Ok, Err};
 use io::Reader;
 
 use rand::Rng;
@@ -49,26 +49,26 @@ impl<R: Reader> Rng for ReaderRng<R> {
         // platform just involves blitting the bytes into the memory
         // of the u32, similarly for BE on BE; avoiding byteswapping.
         if cfg!(target_endian="little") {
-            self.reader.read_le_u32()
+            self.reader.read_le_u32().unwrap()
         } else {
-            self.reader.read_be_u32()
+            self.reader.read_be_u32().unwrap()
         }
     }
     fn next_u64(&mut self) -> u64 {
         // see above for explanation.
         if cfg!(target_endian="little") {
-            self.reader.read_le_u64()
+            self.reader.read_le_u64().unwrap()
         } else {
-            self.reader.read_be_u64()
+            self.reader.read_be_u64().unwrap()
         }
     }
     fn fill_bytes(&mut self, v: &mut [u8]) {
         if v.len() == 0 { return }
         match self.reader.read(v) {
-            Some(n) if n == v.len() => return,
-            Some(n) => fail!("ReaderRng.fill_bytes could not fill buffer: \
-                              read {} out of {} bytes.", n, v.len()),
-            None => fail!("ReaderRng.fill_bytes reached eof.")
+            Ok(n) if n == v.len() => return,
+            Ok(n) => fail!("ReaderRng.fill_bytes could not fill buffer: \
+                            read {} out of {} bytes.", n, v.len()),
+            Err(e) => fail!("ReaderRng.fill_bytes error: {}", e)
         }
     }
 }

src/libstd/reflect.rs

@@ -66,6 +66,8 @@ impl<V:TyVisitor + MovePtr> MovePtrAdaptor<V> {
     pub fn bump_past<T>(&mut self) {
         self.bump(mem::size_of::<T>());
     }
+
+    pub fn unwrap(self) -> V { self.inner }
 }
 
 /// Abstract type-directed pointer-movement using the MovePtr trait

src/libstd/repr.rs

@@ -21,48 +21,57 @@ use char;
 use container::Container;
 use io;
 use iter::Iterator;
-use option::{Some, None};
+use option::{Some, None, Option};
 use ptr;
 use reflect;
 use reflect::{MovePtr, align};
+use result::{Ok, Err};
 use str::StrSlice;
 use to_str::ToStr;
 use vec::OwnedVector;
 use unstable::intrinsics::{Disr, Opaque, TyDesc, TyVisitor, get_tydesc, visit_tydesc};
 use unstable::raw;
 
+macro_rules! if_ok( ($me:expr, $e:expr) => (
+    match $e {
+        Ok(()) => {},
+        Err(e) => { $me.last_err = Some(e); return false; }
+    }
+) )
+
 /// Representations
 
 trait Repr {
-    fn write_repr(&self, writer: &mut io::Writer);
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()>;
 }
 
 impl Repr for () {
-    fn write_repr(&self, writer: &mut io::Writer) {
-        writer.write("()".as_bytes());
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()> {
+        writer.write("()".as_bytes())
     }
 }
 
 impl Repr for bool {
-    fn write_repr(&self, writer: &mut io::Writer) {
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()> {
         let s = if *self { "true" } else { "false" };
         writer.write(s.as_bytes())
     }
 }
 
 impl Repr for int {
-    fn write_repr(&self, writer: &mut io::Writer) {
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()> {
         ::int::to_str_bytes(*self, 10u, |bits| {
-            writer.write(bits);
+            writer.write(bits)
         })
     }
 }
 
 macro_rules! int_repr(($ty:ident, $suffix:expr) => (impl Repr for $ty {
-    fn write_repr(&self, writer: &mut io::Writer) {
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()> {
         ::$ty::to_str_bytes(*self, 10u, |bits| {
-            writer.write(bits);
-            writer.write(bytes!($suffix));
+            writer.write(bits).and_then(|()| {
+                writer.write(bytes!($suffix))
+            })
         })
     }
 }))
@@ -78,10 +87,11 @@ int_repr!(u32, "u32")
 int_repr!(u64, "u64")
 
 macro_rules! num_repr(($ty:ident, $suffix:expr) => (impl Repr for $ty {
-    fn write_repr(&self, writer: &mut io::Writer) {
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()> {
         let s = self.to_str();
-        writer.write(s.as_bytes());
-        writer.write(bytes!($suffix));
+        writer.write(s.as_bytes()).and_then(|()| {
+            writer.write(bytes!($suffix))
+        })
     }
 }))
 
@@ -100,7 +110,8 @@ pub struct ReprVisitor<'a> {
     priv ptr: *u8,
     priv ptr_stk: ~[*u8],
     priv var_stk: ~[VariantState],
-    priv writer: &'a mut io::Writer
+    priv writer: &'a mut io::Writer,
+    priv last_err: Option<io::IoError>,
 }
 
 pub fn ReprVisitor<'a>(ptr: *u8,
@@ -110,6 +121,7 @@ pub fn ReprVisitor<'a>(ptr: *u8,
         ptr_stk: ~[],
         var_stk: ~[],
         writer: writer,
+        last_err: None,
     }
 }
 
@@ -130,11 +142,10 @@ impl<'a> ReprVisitor<'a> {
     // Various helpers for the TyVisitor impl
 
     #[inline]
-    pub fn get<T>(&mut self, f: |&mut ReprVisitor, &T|) -> bool {
+    pub fn get<T>(&mut self, f: |&mut ReprVisitor, &T| -> bool) -> bool {
         unsafe {
-            f(self, transmute::<*u8,&T>(self.ptr));
+            f(self, transmute::<*u8,&T>(self.ptr))
         }
-        true
     }
 
     #[inline]
@@ -152,43 +163,53 @@ impl<'a> ReprVisitor<'a> {
                 ptr_stk: ~[],
                 var_stk: ~[],
                 writer: ::cast::transmute_copy(&self.writer),
+                last_err: None,
             };
             let mut v = reflect::MovePtrAdaptor(u);
             // Obviously this should not be a thing, but blame #8401 for now
             visit_tydesc(inner, &mut v as &mut TyVisitor);
-            true
+            match v.unwrap().last_err {
+                Some(e) => {
+                    self.last_err = Some(e);
+                    false
+                }
+                None => true,
+            }
         }
     }
 
     #[inline]
     pub fn write<T:Repr>(&mut self) -> bool {
         self.get(|this, v:&T| {
-            v.write_repr(unsafe { ::cast::transmute_copy(&this.writer) });
+            if_ok!(this, v.write_repr(this.writer));
+            true
         })
     }
 
-    pub fn write_escaped_slice(&mut self, slice: &str) {
-        self.writer.write(['"' as u8]);
+    pub fn write_escaped_slice(&mut self, slice: &str) -> bool {
+        if_ok!(self, self.writer.write(['"' as u8]));
         for ch in slice.chars() {
-            self.write_escaped_char(ch, true);
+            if !self.write_escaped_char(ch, true) { return false }
         }
-        self.writer.write(['"' as u8]);
+        if_ok!(self, self.writer.write(['"' as u8]));
+        true
     }
 
-    pub fn write_mut_qualifier(&mut self, mtbl: uint) {
+    pub fn write_mut_qualifier(&mut self, mtbl: uint) -> bool {
         if mtbl == 0 {
-            self.writer.write("mut ".as_bytes());
+            if_ok!(self, self.writer.write("mut ".as_bytes()));
         } else if mtbl == 1 {
             // skip, this is ast::m_imm
         } else {
             fail!("invalid mutability value");
         }
+        true
     }
 
     pub fn write_vec_range(&mut self, ptr: *(), len: uint, inner: *TyDesc) -> bool {
         let mut p = ptr as *u8;
         let (sz, al) = unsafe { ((*inner).size, (*inner).align) };
-        self.writer.write(['[' as u8]);
+        if_ok!(self, self.writer.write(['[' as u8]));
         let mut first = true;
         let mut left = len;
         // unit structs have 0 size, and don't loop forever.
@@ -197,13 +218,13 @@ impl<'a> ReprVisitor<'a> {
             if first {
                 first = false;
             } else {
-                self.writer.write(", ".as_bytes());
+                if_ok!(self, self.writer.write(", ".as_bytes()));
             }
             self.visit_ptr_inner(p as *u8, inner);
             p = align(unsafe { ptr::offset(p, sz as int) as uint }, al) as *u8;
             left -= dec;
         }
-        self.writer.write([']' as u8]);
+        if_ok!(self, self.writer.write([']' as u8]));
         true
     }
 
@@ -211,8 +232,8 @@ impl<'a> ReprVisitor<'a> {
         self.write_vec_range(ptr::to_unsafe_ptr(&v.data), v.fill, inner)
     }
 
-    fn write_escaped_char(&mut self, ch: char, is_str: bool) {
-        match ch {
+    fn write_escaped_char(&mut self, ch: char, is_str: bool) -> bool {
+        if_ok!(self, match ch {
             '\t' => self.writer.write("\\t".as_bytes()),
             '\r' => self.writer.write("\\r".as_bytes()),
             '\n' => self.writer.write("\\n".as_bytes()),
@@ -234,16 +255,18 @@ impl<'a> ReprVisitor<'a> {
             '\x20'..'\x7e' => self.writer.write([ch as u8]),
             _ => {
                 char::escape_unicode(ch, |c| {
-                    self.writer.write([c as u8]);
-                })
+                    let _ = self.writer.write([c as u8]);
+                });
+                Ok(())
             }
-        }
+        });
+        return true;
     }
 }
 
 impl<'a> TyVisitor for ReprVisitor<'a> {
     fn visit_bot(&mut self) -> bool {
-        self.writer.write("!".as_bytes());
+        if_ok!(self, self.writer.write("!".as_bytes()));
         true
     }
     fn visit_nil(&mut self) -> bool { self.write::<()>() }
@@ -265,9 +288,10 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
     fn visit_char(&mut self) -> bool {
         self.get::<char>(|this, &ch| {
-            this.writer.write(['\'' as u8]);
-            this.write_escaped_char(ch, false);
-            this.writer.write(['\'' as u8]);
+            if_ok!(this, this.writer.write(['\'' as u8]));
+            if !this.write_escaped_char(ch, false) { return false }
+            if_ok!(this, this.writer.write(['\'' as u8]));
+            true
         })
     }
 
@@ -277,8 +301,8 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
     fn visit_estr_uniq(&mut self) -> bool {
         self.get::<~str>(|this, s| {
-            this.writer.write(['~' as u8]);
-            this.write_escaped_slice(*s);
+            if_ok!(this, this.writer.write(['~' as u8]));
+            this.write_escaped_slice(*s)
         })
     }
 
@@ -291,34 +315,35 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
                         _align: uint) -> bool { fail!(); }
 
     fn visit_box(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
-        self.writer.write(['@' as u8]);
+        if_ok!(self, self.writer.write(['@' as u8]));
         self.write_mut_qualifier(mtbl);
         self.get::<&raw::Box<()>>(|this, b| {
             let p = ptr::to_unsafe_ptr(&b.data) as *u8;
-            this.visit_ptr_inner(p, inner);
+            this.visit_ptr_inner(p, inner)
         })
     }
 
     fn visit_uniq(&mut self, _mtbl: uint, inner: *TyDesc) -> bool {
-        self.writer.write(['~' as u8]);
+        if_ok!(self, self.writer.write(['~' as u8]));
         self.get::<*u8>(|this, b| {
-            this.visit_ptr_inner(*b, inner);
+            this.visit_ptr_inner(*b, inner)
         })
     }
 
     fn visit_ptr(&mut self, mtbl: uint, _inner: *TyDesc) -> bool {
         self.get::<*u8>(|this, p| {
-            write!(this.writer, "({} as *", *p);
+            if_ok!(this, write!(this.writer, "({} as *", *p));
             this.write_mut_qualifier(mtbl);
-            this.writer.write("())".as_bytes());
+            if_ok!(this, this.writer.write("())".as_bytes()));
+            true
         })
     }
 
     fn visit_rptr(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
-        self.writer.write(['&' as u8]);
+        if_ok!(self, self.writer.write(['&' as u8]));
         self.write_mut_qualifier(mtbl);
         self.get::<*u8>(|this, p| {
-            this.visit_ptr_inner(*p, inner);
+            this.visit_ptr_inner(*p, inner)
         })
     }
 
@@ -327,33 +352,33 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
     fn visit_unboxed_vec(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
         self.get::<raw::Vec<()>>(|this, b| {
-            this.write_unboxed_vec_repr(mtbl, b, inner);
+            this.write_unboxed_vec_repr(mtbl, b, inner)
         })
     }
 
     fn visit_evec_box(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
         self.get::<&raw::Box<raw::Vec<()>>>(|this, b| {
-            this.writer.write(['@' as u8]);
+            if_ok!(this, this.writer.write(['@' as u8]));
             this.write_mut_qualifier(mtbl);
-            this.write_unboxed_vec_repr(mtbl, &b.data, inner);
+            this.write_unboxed_vec_repr(mtbl, &b.data, inner)
         })
     }
 
     fn visit_evec_uniq(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
         self.get::<&raw::Vec<()>>(|this, b| {
-            this.writer.write(['~' as u8]);
-            this.write_unboxed_vec_repr(mtbl, *b, inner);
+            if_ok!(this, this.writer.write(['~' as u8]));
+            this.write_unboxed_vec_repr(mtbl, *b, inner)
         })
     }
 
     fn visit_evec_slice(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
         self.get::<raw::Slice<()>>(|this, s| {
-            this.writer.write(['&' as u8]);
+            if_ok!(this, this.writer.write(['&' as u8]));
             this.write_mut_qualifier(mtbl);
             let size = unsafe {
                 if (*inner).size == 0 { 1 } else { (*inner).size }
             };
-            this.write_vec_range(s.data, s.len * size, inner);
+            this.write_vec_range(s.data, s.len * size, inner)
         })
     }
 
@@ -361,42 +386,42 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
                         _: uint, inner: *TyDesc) -> bool {
         let assumed_size = if sz == 0 { n } else { sz };
         self.get::<()>(|this, b| {
-            this.write_vec_range(ptr::to_unsafe_ptr(b), assumed_size, inner);
+            this.write_vec_range(ptr::to_unsafe_ptr(b), assumed_size, inner)
         })
     }
 
     fn visit_enter_rec(&mut self, _n_fields: uint,
                        _sz: uint, _align: uint) -> bool {
-        self.writer.write(['{' as u8]);
+        if_ok!(self, self.writer.write(['{' as u8]));
         true
     }
 
     fn visit_rec_field(&mut self, i: uint, name: &str,
                        mtbl: uint, inner: *TyDesc) -> bool {
         if i != 0 {
-            self.writer.write(", ".as_bytes());
+            if_ok!(self, self.writer.write(", ".as_bytes()));
         }
         self.write_mut_qualifier(mtbl);
-        self.writer.write(name.as_bytes());
-        self.writer.write(": ".as_bytes());
+        if_ok!(self, self.writer.write(name.as_bytes()));
+        if_ok!(self, self.writer.write(": ".as_bytes()));
         self.visit_inner(inner);
         true
     }
 
     fn visit_leave_rec(&mut self, _n_fields: uint,
                        _sz: uint, _align: uint) -> bool {
-        self.writer.write(['}' as u8]);
+        if_ok!(self, self.writer.write(['}' as u8]));
         true
     }
 
     fn visit_enter_class(&mut self, name: &str, named_fields: bool, n_fields: uint,
                          _sz: uint, _align: uint) -> bool {
-        self.writer.write(name.as_bytes());
+        if_ok!(self, self.writer.write(name.as_bytes()));
         if n_fields != 0 {
             if named_fields {
-                self.writer.write(['{' as u8]);
+                if_ok!(self, self.writer.write(['{' as u8]));
             } else {
-                self.writer.write(['(' as u8]);
+                if_ok!(self, self.writer.write(['(' as u8]));
             }
         }
         true
@@ -405,11 +430,11 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
     fn visit_class_field(&mut self, i: uint, name: &str, named: bool,
                          _mtbl: uint, inner: *TyDesc) -> bool {
         if i != 0 {
-            self.writer.write(", ".as_bytes());
+            if_ok!(self, self.writer.write(", ".as_bytes()));
         }
         if named {
-            self.writer.write(name.as_bytes());
-            self.writer.write(": ".as_bytes());
+            if_ok!(self, self.writer.write(name.as_bytes()));
+            if_ok!(self, self.writer.write(": ".as_bytes()));
         }
         self.visit_inner(inner);
         true
@@ -419,9 +444,9 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
                          _sz: uint, _align: uint) -> bool {
         if n_fields != 0 {
             if named_fields {
-                self.writer.write(['}' as u8]);
+                if_ok!(self, self.writer.write(['}' as u8]));
             } else {
-                self.writer.write([')' as u8]);
+                if_ok!(self, self.writer.write([')' as u8]));
             }
         }
         true
@@ -429,13 +454,13 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
     fn visit_enter_tup(&mut self, _n_fields: uint,
                        _sz: uint, _align: uint) -> bool {
-        self.writer.write(['(' as u8]);
+        if_ok!(self, self.writer.write(['(' as u8]));
         true
     }
 
     fn visit_tup_field(&mut self, i: uint, inner: *TyDesc) -> bool {
         if i != 0 {
-            self.writer.write(", ".as_bytes());
+            if_ok!(self, self.writer.write(", ".as_bytes()));
         }
         self.visit_inner(inner);
         true
@@ -444,9 +469,9 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
     fn visit_leave_tup(&mut self, _n_fields: uint,
                        _sz: uint, _align: uint) -> bool {
         if _n_fields == 1 {
-            self.writer.write([',' as u8]);
+            if_ok!(self, self.writer.write([',' as u8]));
         }
-        self.writer.write([')' as u8]);
+        if_ok!(self, self.writer.write([')' as u8]));
         true
     }
 
@@ -482,9 +507,9 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
         }
 
         if write {
-            self.writer.write(name.as_bytes());
+            if_ok!(self, self.writer.write(name.as_bytes()));
             if n_fields > 0 {
-                self.writer.write(['(' as u8]);
+                if_ok!(self, self.writer.write(['(' as u8]));
             }
         }
         true
@@ -498,7 +523,7 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
         match self.var_stk[self.var_stk.len() - 1] {
             Matched => {
                 if i != 0 {
-                    self.writer.write(", ".as_bytes());
+                    if_ok!(self, self.writer.write(", ".as_bytes()));
                 }
                 if ! self.visit_inner(inner) {
                     return false;
@@ -516,7 +541,7 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
         match self.var_stk[self.var_stk.len() - 1] {
             Matched => {
                 if n_fields > 0 {
-                    self.writer.write([')' as u8]);
+                    if_ok!(self, self.writer.write([')' as u8]));
                 }
             }
             _ => ()
@@ -538,28 +563,29 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
     fn visit_enter_fn(&mut self, _purity: uint, _proto: uint,
                       _n_inputs: uint, _retstyle: uint) -> bool {
-        self.writer.write("fn(".as_bytes());
+        if_ok!(self, self.writer.write("fn(".as_bytes()));
         true
     }
 
     fn visit_fn_input(&mut self, i: uint, _mode: uint, inner: *TyDesc) -> bool {
         if i != 0 {
-            self.writer.write(", ".as_bytes());
+            if_ok!(self, self.writer.write(", ".as_bytes()));
         }
         let name = unsafe { (*inner).name };
-        self.writer.write(name.as_bytes());
+        if_ok!(self, self.writer.write(name.as_bytes()));
         true
     }
 
-    fn visit_fn_output(&mut self, _retstyle: uint, variadic: bool, inner: *TyDesc) -> bool {
+    fn visit_fn_output(&mut self, _retstyle: uint, variadic: bool,
+                       inner: *TyDesc) -> bool {
         if variadic {
-            self.writer.write(", ...".as_bytes());
+            if_ok!(self, self.writer.write(", ...".as_bytes()));
         }
-        self.writer.write(")".as_bytes());
+        if_ok!(self, self.writer.write(")".as_bytes()));
         let name = unsafe { (*inner).name };
         if name != "()" {
-            self.writer.write(" -> ".as_bytes());
-            self.writer.write(name.as_bytes());
+            if_ok!(self, self.writer.write(" -> ".as_bytes()));
+            if_ok!(self, self.writer.write(name.as_bytes()));
         }
         true
     }
@@ -569,7 +595,7 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
 
     fn visit_trait(&mut self, name: &str) -> bool {
-        self.writer.write(name.as_bytes());
+        if_ok!(self, self.writer.write(name.as_bytes()));
         true
     }
 
@@ -582,13 +608,17 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
     fn visit_closure_ptr(&mut self, _ck: uint) -> bool { true }
 }
 
-pub fn write_repr<T>(writer: &mut io::Writer, object: &T) {
+pub fn write_repr<T>(writer: &mut io::Writer, object: &T) -> io::IoResult<()> {
     unsafe {
         let ptr = ptr::to_unsafe_ptr(object) as *u8;
         let tydesc = get_tydesc::<T>();
         let u = ReprVisitor(ptr, writer);
         let mut v = reflect::MovePtrAdaptor(u);
         visit_tydesc(tydesc, &mut v as &mut TyVisitor);
+        match v.unwrap().last_err {
+            Some(e) => Err(e),
+            None => Ok(()),
+        }
     }
 }
 
@@ -597,7 +627,7 @@ pub fn repr_to_str<T>(t: &T) -> ~str {
     use io;
 
     let mut result = io::MemWriter::new();
-    write_repr(&mut result as &mut io::Writer, t);
+    write_repr(&mut result as &mut io::Writer, t).unwrap();
     str::from_utf8_owned(result.unwrap()).unwrap()
 }
 
@@ -615,7 +645,7 @@ fn test_repr() {
 
     fn exact_test<T>(t: &T, e:&str) {
         let mut m = io::MemWriter::new();
-        write_repr(&mut m as &mut io::Writer, t);
+        write_repr(&mut m as &mut io::Writer, t).unwrap();
         let s = str::from_utf8_owned(m.unwrap()).unwrap();
         assert_eq!(s.as_slice(), e);
     }

src/libstd/result.rs

@@ -208,7 +208,7 @@ impl<T, E> Result<T, E> {
 
 impl<T: fmt::Show, E: fmt::Show> fmt::Show for Result<T, E> {
     #[inline]
-    fn fmt(s: &Result<T, E>, f: &mut fmt::Formatter) {
+    fn fmt(s: &Result<T, E>, f: &mut fmt::Formatter) -> fmt::Result {
         match *s {
             Ok(ref t) => write!(f.buf, "Ok({})", *t),
             Err(ref e) => write!(f.buf, "Err({})", *e)

src/libstd/rt/rtio.rs

@@ -16,13 +16,13 @@ use libc;
 use ops::Drop;
 use option::{Option, Some, None};
 use path::Path;
-use result::{Result, Ok, Err};
+use result::{Result, Err};
 use rt::task::Task;
 use rt::local::Local;
 
 use ai = io::net::addrinfo;
 use io;
-use io::IoError;
+use io::{IoError, IoResult};
 use io::net::ip::{IpAddr, SocketAddr};
 use io::process::{ProcessConfig, ProcessExit};
 use io::signal::Signum;
@@ -116,23 +116,12 @@ impl<'a> LocalIo<'a> {
         return ret;
     }
 
-    pub fn maybe_raise<T>(f: |io: &mut IoFactory| -> Result<T, IoError>)
-        -> Option<T>
+    pub fn maybe_raise<T>(f: |io: &mut IoFactory| -> IoResult<T>)
+        -> IoResult<T>
     {
         match LocalIo::borrow() {
-            None => {
-                io::io_error::cond.raise(io::standard_error(io::IoUnavailable));
-                None
-            }
-            Some(mut io) => {
-                match f(io.get()) {
-                    Ok(t) => Some(t),
-                    Err(ioerr) => {
-                        io::io_error::cond.raise(ioerr);
-                        None
-                    }
-                }
-            }
+            None => Err(io::standard_error(io::IoUnavailable)),
+            Some(mut io) => f(io.get()),
         }
     }
 

src/libstd/rt/task.rs

@@ -119,6 +119,7 @@ impl Task {
 
             // Run the task main function, then do some cleanup.
             f.finally(|| {
+                #[allow(unused_must_use)]
                 fn close_outputs() {
                     let mut task = Local::borrow(None::<Task>);
                     let logger = task.get().logger.take();
@@ -126,8 +127,8 @@ impl Task {
                     let stdout = task.get().stdout.take();
                     drop(task);
                     drop(logger); // loggers are responsible for flushing
-                    match stdout { Some(mut w) => w.flush(), None => {} }
-                    match stderr { Some(mut w) => w.flush(), None => {} }
+                    match stdout { Some(mut w) => { w.flush(); }, None => {} }
+                    match stderr { Some(mut w) => { w.flush(); }, None => {} }
                 }
 
                 // First, flush/destroy the user stdout/logger because these

src/libstd/rt/unwind.rs

@@ -464,9 +464,10 @@ fn begin_unwind_inner(msg: ~Any, file: &'static str, line: uint) -> ! {
             match task.stderr.take() {
                 Some(mut stderr) => {
                     Local::put(task);
-                    format_args!(|args| ::fmt::writeln(stderr, args),
-                                 "task '{}' failed at '{}', {}:{}",
-                                 n, msg_s, file, line);
+                    // FIXME: what to do when the task printing fails?
+                    let _err = format_args!(|args| ::fmt::writeln(stderr, args),
+                                            "task '{}' failed at '{}', {}:{}",
+                                            n, msg_s, file, line);
                     task = Local::take();
 
                     match util::replace(&mut task.stderr, Some(stderr)) {

src/libstd/rt/util.rs

@@ -11,10 +11,12 @@
 use container::Container;
 use fmt;
 use from_str::FromStr;
+use io::IoResult;
 use iter::Iterator;
 use libc;
 use option::{Some, None, Option};
 use os;
+use result::Ok;
 use str::StrSlice;
 use unstable::running_on_valgrind;
 use vec::ImmutableVector;
@@ -73,16 +75,17 @@ pub fn dumb_println(args: &fmt::Arguments) {
 
     struct Stderr;
     impl io::Writer for Stderr {
-        fn write(&mut self, data: &[u8]) {
+        fn write(&mut self, data: &[u8]) -> IoResult<()> {
             unsafe {
                 libc::write(libc::STDERR_FILENO,
                             data.as_ptr() as *libc::c_void,
                             data.len() as libc::size_t);
             }
+            Ok(()) // yes, we're lying
         }
     }
     let mut w = Stderr;
-    fmt::writeln(&mut w as &mut io::Writer, args);
+    let _ = fmt::writeln(&mut w as &mut io::Writer, args);
 }
 
 pub fn abort(msg: &str) -> ! {

src/libstd/run.rs

@@ -11,6 +11,7 @@
 //! Utilities for spawning and managing processes
 
 #[allow(missing_doc)];
+#[deny(unused_must_use)];
 
 use comm::SharedChan;
 use io::Reader;
@@ -119,7 +120,8 @@ impl Process {
      * * options - Options to configure the environment of the process,
      *             the working directory and the standard IO streams.
      */
-    pub fn new(prog: &str, args: &[~str], options: ProcessOptions) -> Option<Process> {
+    pub fn new(prog: &str, args: &[~str],
+               options: ProcessOptions) -> io::IoResult<Process> {
         let ProcessOptions { env, dir, in_fd, out_fd, err_fd } = options;
         let env = env.as_ref().map(|a| a.as_slice());
         let cwd = dir.as_ref().map(|a| a.as_str().unwrap());
@@ -138,10 +140,7 @@ impl Process {
             cwd: cwd,
             io: rtio,
         };
-        match process::Process::new(rtconfig) {
-            Some(inner) => Some(Process { inner: inner }),
-            None => None
-        }
+        process::Process::new(rtconfig).map(|p| Process { inner: p })
     }
 
     /// Returns the unique id of the process
@@ -224,19 +223,17 @@ impl Process {
         let ch_clone = ch.clone();
 
         spawn(proc() {
-            let _guard = io::ignore_io_error();
             let mut error = error;
             match error {
                 Some(ref mut e) => ch.send((2, e.read_to_end())),
-                None => ch.send((2, ~[]))
+                None => ch.send((2, Ok(~[])))
             }
         });
         spawn(proc() {
-            let _guard = io::ignore_io_error();
             let mut output = output;
             match output {
                 Some(ref mut e) => ch_clone.send((1, e.read_to_end())),
-                None => ch_clone.send((1, ~[]))
+                None => ch_clone.send((1, Ok(~[])))
             }
         });
 
@@ -251,8 +248,8 @@ impl Process {
         };
 
         return ProcessOutput {status: status,
-                              output: outs,
-                              error: errs};
+                              output: outs.ok().unwrap_or(~[]),
+                              error: errs.ok().unwrap_or(~[]) };
     }
 
     /**
@@ -262,9 +259,10 @@ impl Process {
      * On Posix OSs SIGTERM will be sent to the process. On Win32
      * TerminateProcess(..) will be called.
      */
-    pub fn destroy(&mut self) {
-        self.inner.signal(io::process::PleaseExitSignal);
+    pub fn destroy(&mut self) -> io::IoResult<()> {
+        let ret = self.inner.signal(io::process::PleaseExitSignal);
         self.finish();
+        return ret;
     }
 
     /**
@@ -274,9 +272,12 @@ impl Process {
      * On Posix OSs SIGKILL will be sent to the process. On Win32
      * TerminateProcess(..) will be called.
      */
-    pub fn force_destroy(&mut self) {
-        self.inner.signal(io::process::MustDieSignal);
+    pub fn force_destroy(&mut self) -> io::IoResult<()> {
+        // This should never fail because we own the process
+        let ret = self.inner.signal(io::process::MustDieSignal);
         self.finish();
+        return ret;
+
     }
 }
 
@@ -293,18 +294,14 @@ impl Process {
  *
  * The process's exit code, or None if the child process could not be started
  */
-pub fn process_status(prog: &str, args: &[~str]) -> Option<ProcessExit> {
-    let mut opt_prog = Process::new(prog, args, ProcessOptions {
+pub fn process_status(prog: &str, args: &[~str]) -> io::IoResult<ProcessExit> {
+    Process::new(prog, args, ProcessOptions {
         env: None,
         dir: None,
         in_fd: Some(unsafe { libc::dup(libc::STDIN_FILENO) }),
         out_fd: Some(unsafe { libc::dup(libc::STDOUT_FILENO) }),
         err_fd: Some(unsafe { libc::dup(libc::STDERR_FILENO) })
-    });
-    match opt_prog {
-        Some(ref mut prog) => Some(prog.finish()),
-        None => None
-    }
+    }).map(|mut p| p.finish())
 }
 
 /**
@@ -320,12 +317,10 @@ pub fn process_status(prog: &str, args: &[~str]) -> Option<ProcessExit> {
  * The process's stdout/stderr output and exit code, or None if the child process could not be
  * started.
  */
-pub fn process_output(prog: &str, args: &[~str]) -> Option<ProcessOutput> {
-    let mut opt_prog = Process::new(prog, args, ProcessOptions::new());
-    match opt_prog {
-        Some(ref mut prog) => Some(prog.finish_with_output()),
-        None => None
-    }
+pub fn process_output(prog: &str, args: &[~str]) -> io::IoResult<ProcessOutput> {
+    Process::new(prog, args, ProcessOptions::new()).map(|mut p| {
+        p.finish_with_output()
+    })
 }
 
 #[cfg(test)]
@@ -337,33 +332,25 @@ mod tests {
     use task::spawn;
     use unstable::running_on_valgrind;
     use io::pipe::PipeStream;
-    use io::{io_error, FileNotFound};
+    use io::{FileNotFound};
     use libc::c_int;
 
     #[test]
     #[cfg(not(target_os="android"))] // FIXME(#10380)
     fn test_process_status() {
-        let mut status = run::process_status("false", []).expect("failed to exec `false`");
+        let mut status = run::process_status("false", []).unwrap();
         assert!(status.matches_exit_status(1));
 
-        status = run::process_status("true", []).expect("failed to exec `true`");
+        status = run::process_status("true", []).unwrap();
         assert!(status.success());
     }
 
     #[test]
     fn test_process_output_fail_to_start() {
-        // If the executable does not exist, then the io_error condition should be raised with
-        // IoErrorKind FileNotFound.
-
-        let mut trapped_io_error = false;
-        let opt_outp = io_error::cond.trap(|e| {
-            trapped_io_error = true;
-            assert_eq!(e.kind, FileNotFound);
-        }).inside(|| -> Option<run::ProcessOutput> {
-            run::process_output("/no-binary-by-this-name-should-exist", [])
-        });
-        assert!(trapped_io_error);
-        assert!(opt_outp.is_none());
+        match run::process_output("/no-binary-by-this-name-should-exist", []) {
+            Err(e) => assert_eq!(e.kind, FileNotFound),
+            Ok(..) => fail!()
+        }
     }
 
     #[test]
@@ -371,7 +358,7 @@ mod tests {
     fn test_process_output_output() {
 
         let run::ProcessOutput {status, output, error}
-             = run::process_output("echo", [~"hello"]).expect("failed to exec `echo`");
+             = run::process_output("echo", [~"hello"]).unwrap();
         let output_str = str::from_utf8_owned(output).unwrap();
 
         assert!(status.success());
@@ -387,7 +374,7 @@ mod tests {
     fn test_process_output_error() {
 
         let run::ProcessOutput {status, output, error}
-             = run::process_output("mkdir", [~"."]).expect("failed to exec `mkdir`");
+             = run::process_output("mkdir", [~"."]).unwrap();
 
         assert!(status.matches_exit_status(1));
         assert_eq!(output, ~[]);
@@ -408,7 +395,7 @@ mod tests {
             in_fd: Some(pipe_in.input),
             out_fd: Some(pipe_out.out),
             err_fd: Some(pipe_err.out)
-        }).expect("failed to exec `cat`");
+        }).unwrap();
 
         os::close(pipe_in.input as int);
         os::close(pipe_out.out as int);
@@ -426,27 +413,18 @@ mod tests {
 
     fn writeclose(fd: c_int, s: &str) {
         let mut writer = PipeStream::open(fd);
-        writer.write(s.as_bytes());
+        writer.write(s.as_bytes()).unwrap();
     }
 
     fn readclose(fd: c_int) -> ~str {
-        let mut res = ~[];
-        let mut reader = PipeStream::open(fd);
-        let mut buf = [0, ..1024];
-        loop {
-            match reader.read(buf) {
-                Some(n) => { res.push_all(buf.slice_to(n)); }
-                None => break
-            }
-        }
-        str::from_utf8_owned(res).unwrap()
+        PipeStream::open(fd).read_to_str().unwrap()
     }
 
     #[test]
     #[cfg(not(target_os="android"))] // FIXME(#10380)
     fn test_finish_once() {
         let mut prog = run::Process::new("false", [], run::ProcessOptions::new())
-            .expect("failed to exec `false`");
+            .unwrap();
         assert!(prog.finish().matches_exit_status(1));
     }
 
@@ -454,7 +432,7 @@ mod tests {
     #[cfg(not(target_os="android"))] // FIXME(#10380)
     fn test_finish_twice() {
         let mut prog = run::Process::new("false", [], run::ProcessOptions::new())
-            .expect("failed to exec `false`");
+            .unwrap();
         assert!(prog.finish().matches_exit_status(1));
         assert!(prog.finish().matches_exit_status(1));
     }
@@ -464,7 +442,7 @@ mod tests {
     fn test_finish_with_output_once() {
 
         let mut prog = run::Process::new("echo", [~"hello"], run::ProcessOptions::new())
-            .expect("failed to exec `echo`");
+            .unwrap();
         let run::ProcessOutput {status, output, error}
             = prog.finish_with_output();
         let output_str = str::from_utf8_owned(output).unwrap();
@@ -482,7 +460,7 @@ mod tests {
     fn test_finish_with_output_twice() {
 
         let mut prog = run::Process::new("echo", [~"hello"], run::ProcessOptions::new())
-            .expect("failed to exec `echo`");
+            .unwrap();
         let run::ProcessOutput {status, output, error}
             = prog.finish_with_output();
 
@@ -511,14 +489,14 @@ mod tests {
         run::Process::new("pwd", [], run::ProcessOptions {
             dir: dir,
             .. run::ProcessOptions::new()
-        }).expect("failed to exec `pwd`")
+        }).unwrap()
     }
     #[cfg(unix,target_os="android")]
     fn run_pwd(dir: Option<&Path>) -> run::Process {
         run::Process::new("/system/bin/sh", [~"-c",~"pwd"], run::ProcessOptions {
             dir: dir,
             .. run::ProcessOptions::new()
-        }).expect("failed to exec `/system/bin/sh`")
+        }).unwrap()
     }
 
     #[cfg(windows)]
@@ -526,7 +504,7 @@ mod tests {
         run::Process::new("cmd", [~"/c", ~"cd"], run::ProcessOptions {
             dir: dir,
             .. run::ProcessOptions::new()
-        }).expect("failed to run `cmd`")
+        }).unwrap()
     }
 
     #[test]
@@ -537,8 +515,8 @@ mod tests {
         let parent_dir = os::getcwd();
         let child_dir = Path::new(output.trim());
 
-        let parent_stat = parent_dir.stat();
-        let child_stat = child_dir.stat();
+        let parent_stat = parent_dir.stat().unwrap();
+        let child_stat = child_dir.stat().unwrap();
 
         assert_eq!(parent_stat.unstable.device, child_stat.unstable.device);
         assert_eq!(parent_stat.unstable.inode, child_stat.unstable.inode);
@@ -554,8 +532,8 @@ mod tests {
         let output = str::from_utf8_owned(prog.finish_with_output().output).unwrap();
         let child_dir = Path::new(output.trim());
 
-        let parent_stat = parent_dir.stat();
-        let child_stat = child_dir.stat();
+        let parent_stat = parent_dir.stat().unwrap();
+        let child_stat = child_dir.stat().unwrap();
 
         assert_eq!(parent_stat.unstable.device, child_stat.unstable.device);
         assert_eq!(parent_stat.unstable.inode, child_stat.unstable.inode);
@@ -566,14 +544,14 @@ mod tests {
         run::Process::new("env", [], run::ProcessOptions {
             env: env,
             .. run::ProcessOptions::new()
-        }).expect("failed to exec `env`")
+        }).unwrap()
     }
     #[cfg(unix,target_os="android")]
     fn run_env(env: Option<~[(~str, ~str)]>) -> run::Process {
         run::Process::new("/system/bin/sh", [~"-c",~"set"], run::ProcessOptions {
             env: env,
             .. run::ProcessOptions::new()
-        }).expect("failed to exec `/system/bin/sh`")
+        }).unwrap()
     }
 
     #[cfg(windows)]
@@ -581,7 +559,7 @@ mod tests {
         run::Process::new("cmd", [~"/c", ~"set"], run::ProcessOptions {
             env: env,
             .. run::ProcessOptions::new()
-        }).expect("failed to run `cmd`")
+        }).unwrap()
     }
 
     #[test]

src/libstd/task.rs

@@ -541,7 +541,7 @@ fn test_avoid_copying_the_body_task_spawn() {
 #[test]
 fn test_avoid_copying_the_body_try() {
     avoid_copying_the_body(|f| {
-        try(proc() {
+        let _ = try(proc() {
             f()
         });
     })

src/libstd/to_bytes.rs

@@ -349,7 +349,7 @@ impl<A:IterBytes> ToBytes for A {
 
         let mut m = ::io::MemWriter::new();
         self.iter_bytes(lsb0, |bytes| {
-            m.write(bytes);
+            m.write(bytes).unwrap();
             true
         });
         m.unwrap()

src/libstd/unstable/sync.rs

@@ -200,7 +200,7 @@ mod tests {
             // accesses will also fail.
             let x = Exclusive::new(1);
             let x2 = x.clone();
-            task::try(proc() {
+            let _ = task::try(proc() {
                 x2.with(|one| assert_eq!(*one, 2))
             });
             x.with(|one| assert_eq!(*one, 1));

src/libsyntax/diagnostic.rs

@@ -189,58 +189,61 @@ impl Level {
     }
 }
 
-fn print_maybe_styled(msg: &str, color: term::attr::Attr) {
-    local_data_key!(tls_terminal: ~Option<term::Terminal<StdWriter>>)
+fn print_maybe_styled(msg: &str, color: term::attr::Attr) -> io::IoResult<()> {
+    local_data_key!(tls_terminal: Option<term::Terminal<StdWriter>>)
+
 
     fn is_stderr_screen() -> bool {
         use std::libc;
         unsafe { libc::isatty(libc::STDERR_FILENO) != 0 }
     }
-    fn write_pretty<T: Writer>(term: &mut term::Terminal<T>, s: &str, c: term::attr::Attr) {
-        term.attr(c);
-        term.write(s.as_bytes());
-        term.reset();
+    fn write_pretty<T: Writer>(term: &mut term::Terminal<T>, s: &str,
+                               c: term::attr::Attr) -> io::IoResult<()> {
+        if_ok!(term.attr(c));
+        if_ok!(term.write(s.as_bytes()));
+        if_ok!(term.reset());
+        Ok(())
     }
 
     if is_stderr_screen() {
         local_data::get_mut(tls_terminal, |term| {
             match term {
                 Some(term) => {
-                    match **term {
+                    match *term {
                         Some(ref mut term) => write_pretty(term, msg, color),
                         None => io::stderr().write(msg.as_bytes())
                     }
                 }
                 None => {
-                    let t = ~match term::Terminal::new(io::stderr()) {
+                    let (t, ret) = match term::Terminal::new(io::stderr()) {
                         Ok(mut term) => {
-                            write_pretty(&mut term, msg, color);
-                            Some(term)
+                            let r = write_pretty(&mut term, msg, color);
+                            (Some(term), r)
                         }
                         Err(_) => {
-                            io::stderr().write(msg.as_bytes());
-                            None
+                            (None, io::stderr().write(msg.as_bytes()))
                         }
                     };
                     local_data::set(tls_terminal, t);
+                    ret
                 }
             }
-        });
+        })
     } else {
-        io::stderr().write(msg.as_bytes());
+        io::stderr().write(msg.as_bytes())
     }
 }
 
-fn print_diagnostic(topic: &str, lvl: Level, msg: &str) {
-    let mut stderr = io::stderr();
-
+fn print_diagnostic(topic: &str, lvl: Level, msg: &str) -> io::IoResult<()> {
     if !topic.is_empty() {
-        write!(&mut stderr as &mut io::Writer, "{} ", topic);
+        let mut stderr = io::stderr();
+        if_ok!(write!(&mut stderr as &mut io::Writer, "{} ", topic));
     }
 
-    print_maybe_styled(format!("{}: ", lvl.to_str()),
-                       term::attr::ForegroundColor(lvl.color()));
-    print_maybe_styled(format!("{}\n", msg), term::attr::Bold);
+    if_ok!(print_maybe_styled(format!("{}: ", lvl.to_str()),
+                              term::attr::ForegroundColor(lvl.color())));
+    if_ok!(print_maybe_styled(format!("{}\n", msg), term::attr::Bold));
+    Ok(())
 }
 
 pub struct DefaultEmitter;
@@ -250,20 +253,28 @@ impl Emitter for DefaultEmitter {
             cmsp: Option<(&codemap::CodeMap, Span)>,
             msg: &str,
             lvl: Level) {
-        match cmsp {
+        let error = match cmsp {
             Some((cm, sp)) => emit(cm, sp, msg, lvl, false),
             None => print_diagnostic("", lvl, msg),
+        };
+
+        match error {
+            Ok(()) => {}
+            Err(e) => fail!("failed to print diagnostics: {}", e),
         }
     }
 
     fn custom_emit(&self, cm: &codemap::CodeMap,
                    sp: Span, msg: &str, lvl: Level) {
-        emit(cm, sp, msg, lvl, true);
+        match emit(cm, sp, msg, lvl, true) {
+            Ok(()) => {}
+            Err(e) => fail!("failed to print diagnostics: {}", e),
+        }
     }
 }
 
 fn emit(cm: &codemap::CodeMap, sp: Span,
-        msg: &str, lvl: Level, custom: bool) {
+        msg: &str, lvl: Level, custom: bool) -> io::IoResult<()> {
     let ss = cm.span_to_str(sp);
     let lines = cm.span_to_lines(sp);
     if custom {
@@ -272,19 +283,19 @@ fn emit(cm: &codemap::CodeMap, sp: Span,
         // the span)
         let span_end = Span { lo: sp.hi, hi: sp.hi, expn_info: sp.expn_info};
         let ses = cm.span_to_str(span_end);
-        print_diagnostic(ses, lvl, msg);
-        custom_highlight_lines(cm, sp, lvl, lines);
+        if_ok!(print_diagnostic(ses, lvl, msg));
+        if_ok!(custom_highlight_lines(cm, sp, lvl, lines));
     } else {
-        print_diagnostic(ss, lvl, msg);
-        highlight_lines(cm, sp, lvl, lines);
+        if_ok!(print_diagnostic(ss, lvl, msg));
+        if_ok!(highlight_lines(cm, sp, lvl, lines));
     }
-    print_macro_backtrace(cm, sp);
+    print_macro_backtrace(cm, sp)
 }
 
 fn highlight_lines(cm: &codemap::CodeMap,
                    sp: Span,
                    lvl: Level,
-                   lines: &codemap::FileLines) {
+                   lines: &codemap::FileLines) -> io::IoResult<()> {
     let fm = lines.file;
     let mut err = io::stderr();
     let err = &mut err as &mut io::Writer;
@@ -297,12 +308,13 @@ fn highlight_lines(cm: &codemap::CodeMap,
     }
     // Print the offending lines
     for line in display_lines.iter() {
-        write!(err, "{}:{} {}\n", fm.name, *line + 1, fm.get_line(*line as int));
+        if_ok!(write!(err, "{}:{} {}\n", fm.name, *line + 1,
+                      fm.get_line(*line as int)));
     }
     if elided {
         let last_line = display_lines[display_lines.len() - 1u];
         let s = format!("{}:{} ", fm.name, last_line + 1u);
-        write!(err, "{0:1$}...\n", "", s.len());
+        if_ok!(write!(err, "{0:1$}...\n", "", s.len()));
     }
 
     // FIXME (#3260)
@@ -334,7 +346,7 @@ fn highlight_lines(cm: &codemap::CodeMap,
                 _ => s.push_char(' '),
             };
         }
-        write!(err, "{}", s);
+        if_ok!(write!(err, "{}", s));
         let mut s = ~"^";
         let hi = cm.lookup_char_pos(sp.hi);
         if hi.col != lo.col {
@@ -342,8 +354,10 @@ fn highlight_lines(cm: &codemap::CodeMap,
             let num_squigglies = hi.col.to_uint()-lo.col.to_uint()-1u;
             for _ in range(0, num_squigglies) { s.push_char('~'); }
         }
-        print_maybe_styled(s + "\n", term::attr::ForegroundColor(lvl.color()));
+        if_ok!(print_maybe_styled(s + "\n",
+                                  term::attr::ForegroundColor(lvl.color())));
     }
+    Ok(())
 }
 
 // Here are the differences between this and the normal `highlight_lines`:
@@ -355,23 +369,23 @@ fn highlight_lines(cm: &codemap::CodeMap,
 fn custom_highlight_lines(cm: &codemap::CodeMap,
                           sp: Span,
                           lvl: Level,
-                          lines: &codemap::FileLines) {
+                          lines: &codemap::FileLines) -> io::IoResult<()> {
     let fm = lines.file;
     let mut err = io::stderr();
     let err = &mut err as &mut io::Writer;
 
     let lines = lines.lines.as_slice();
     if lines.len() > MAX_LINES {
-        write!(err, "{}:{} {}\n", fm.name,
-               lines[0] + 1, fm.get_line(lines[0] as int));
-        write!(err, "...\n");
+        if_ok!(write!(err, "{}:{} {}\n", fm.name,
+                      lines[0] + 1, fm.get_line(lines[0] as int)));
+        if_ok!(write!(err, "...\n"));
         let last_line = lines[lines.len()-1];
-        write!(err, "{}:{} {}\n", fm.name,
-               last_line + 1, fm.get_line(last_line as int));
+        if_ok!(write!(err, "{}:{} {}\n", fm.name,
+                      last_line + 1, fm.get_line(last_line as int)));
     } else {
         for line in lines.iter() {
-            write!(err, "{}:{} {}\n", fm.name,
-                   *line + 1, fm.get_line(*line as int));
+            if_ok!(write!(err, "{}:{} {}\n", fm.name,
+                          *line + 1, fm.get_line(*line as int)));
         }
     }
     let last_line_start = format!("{}:{} ", fm.name, lines[lines.len()-1]+1);
@@ -381,22 +395,24 @@ fn custom_highlight_lines(cm: &codemap::CodeMap,
     let mut s = ~"";
     for _ in range(0, skip) { s.push_char(' '); }
     s.push_char('^');
-    print_maybe_styled(s + "\n", term::attr::ForegroundColor(lvl.color()));
+    print_maybe_styled(s + "\n", term::attr::ForegroundColor(lvl.color()))
 }
 
-fn print_macro_backtrace(cm: &codemap::CodeMap, sp: Span) {
+fn print_macro_backtrace(cm: &codemap::CodeMap, sp: Span) -> io::IoResult<()> {
     for ei in sp.expn_info.iter() {
         let ss = ei.callee.span.as_ref().map_or(~"", |span| cm.span_to_str(*span));
         let (pre, post) = match ei.callee.format {
             codemap::MacroAttribute => ("#[", "]"),
             codemap::MacroBang => ("", "!")
         };
-        print_diagnostic(ss, Note,
-                         format!("in expansion of {}{}{}", pre, ei.callee.name, post));
+        if_ok!(print_diagnostic(ss, Note,
+                                format!("in expansion of {}{}{}", pre,
+                                        ei.callee.name, post)));
         let ss = cm.span_to_str(ei.call_site);
-        print_diagnostic(ss, Note, "expansion site");
-        print_macro_backtrace(cm, ei.call_site);
+        if_ok!(print_diagnostic(ss, Note, "expansion site"));
+        if_ok!(print_macro_backtrace(cm, ei.call_site));
     }
+    Ok(())
 }
 
 pub fn expect<T:Clone>(diag: @SpanHandler, opt: Option<T>, msg: || -> ~str)