auto merge of #13107 : seanmonstar/rust/encoder-errors, r=erickt

All of Decoder and Encoder's methods now return a Result.

Encodable.encode() and Decodable.decode() return a Result as well.

fixes #12292

src/librustdoc/lib.rs

@@ -327,6 +327,17 @@ fn rust_input(cratefile: &str, matches: &getopts::Matches) -> Output {
     return pm.run_plugins(krate);
 }
 
+// FIXME: remove unwrap_ after snapshot
+#[cfg(stage0)]
+fn unwrap_<T>(t: T) -> T {
+    t
+}
+
+#[cfg(not(stage0))]
+fn unwrap_<T, E>(r: Result<T, E>) -> T {
+    r.unwrap()
+}
+
 /// This input format purely deserializes the json output file. No passes are
 /// run over the deserialized output.
 fn json_input(input: &str) -> Result<Output, ~str> {
@@ -352,7 +363,7 @@ fn json_input(input: &str) -> Result<Output, ~str> {
             let krate = match obj.pop(&~"crate") {
                 Some(json) => {
                     let mut d = json::Decoder::new(json);
-                    Decodable::decode(&mut d)
+                    unwrap_(Decodable::decode(&mut d))
                 }
                 None => return Err(~"malformed json"),
             };
@@ -384,7 +395,7 @@ fn json_output(krate: clean::Crate, res: Vec<plugins::PluginJson> ,
         let mut w = MemWriter::new();
         {
             let mut encoder = json::Encoder::new(&mut w as &mut io::Writer);
-            krate.encode(&mut encoder);
+            unwrap_(krate.encode(&mut encoder));
         }
         str::from_utf8_owned(w.unwrap()).unwrap()
     };