Rollup merge of #47328 - mbrubeck:fs_read, r=sfackler

Use the new fs_read_write functions in rustc internals

Uses `fs::read` and `fs::write` (added by #45837) where appropriate, to simplify code and dog-food these new APIs.  This also improves performance, when combined with #47324.

src/librustc_incremental/assert_dep_graph.rs

@@ -55,7 +55,7 @@ use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc::ich::{ATTR_IF_THIS_CHANGED, ATTR_THEN_THIS_WOULD_NEED};
 use graphviz::IntoCow;
 use std::env;
-use std::fs::File;
+use std::fs::{self, File};
 use std::io::Write;
 use syntax::ast;
 use syntax_pos::Span;
@@ -260,7 +260,7 @@ fn dump_graph(tcx: TyCtxt) {
         let dot_path = format!("{}.dot", path);
         let mut v = Vec::new();
         dot::render(&GraphvizDepGraph(nodes, edges), &mut v).unwrap();
-        File::create(&dot_path).and_then(|mut f| f.write_all(&v)).unwrap();
+        fs::write(dot_path, v).unwrap();
     }
 }
 

src/librustc_incremental/lib.rs

@@ -16,6 +16,7 @@
 #![deny(warnings)]
 
 #![feature(conservative_impl_trait)]
+#![feature(fs_read_write)]
 #![feature(i128_type)]
 #![feature(inclusive_range_syntax)]
 #![feature(specialization)]

src/librustc_incremental/persist/file_format.rs

@@ -21,7 +21,7 @@
 
 use std::io::{self, Read};
 use std::path::Path;
-use std::fs::File;
+use std::fs;
 use std::env;
 
 use rustc::session::config::nightly_options;
@@ -66,11 +66,7 @@ pub fn read_file(report_incremental_info: bool, path: &Path)
         return Ok(None);
     }
 
-    let mut file = File::open(path)?;
-    let file_size = file.metadata()?.len() as usize;
-
-    let mut data = Vec::with_capacity(file_size);
-    file.read_to_end(&mut data)?;
+    let data = fs::read(path)?;
 
     let mut file = io::Cursor::new(data);
 

src/librustc_incremental/persist/save.rs

@@ -15,8 +15,8 @@ use rustc::util::common::time;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_serialize::Encodable as RustcEncodable;
 use rustc_serialize::opaque::Encoder;
-use std::io::{self, Cursor, Write};
-use std::fs::{self, File};
+use std::io::{self, Cursor};
+use std::fs;
 use std::path::PathBuf;
 
 use super::data::*;
@@ -125,7 +125,7 @@ fn save_in<F>(sess: &Session, path_buf: PathBuf, encode: F)
 
     // write the data out
     let data = wr.into_inner();
-    match File::create(&path_buf).and_then(|mut file| file.write_all(&data)) {
+    match fs::write(&path_buf, data) {
         Ok(_) => {
             debug!("save: data written to disk successfully");
         }