use top level fs functions where appropriate

This commit replaces many usages of `File::open` and reading or writing
with `fs::read_to_string`, `fs::read` and `fs::write`. This reduces code
complexity, and will improve performance for most reads, since the
functions allocate the buffer to be the size of the file.

I believe that this commit will not impact behavior in any way, so some
matches will check the error kind in case the file was not valid UTF-8.
Some of these cases may not actually care about the error.

src/bootstrap/compile.rs

@@ -18,7 +18,7 @@
 
 use std::borrow::Cow;
 use std::env;
-use std::fs::{self, File};
+use std::fs;
 use std::io::BufReader;
 use std::io::prelude::*;
 use std::path::{Path, PathBuf};
@@ -707,7 +707,7 @@ impl Step for CodegenBackend {
         }
         let stamp = codegen_backend_stamp(builder, compiler, target, backend);
         let codegen_backend = codegen_backend.to_str().unwrap();
-        t!(t!(File::create(&stamp)).write_all(codegen_backend.as_bytes()));
+        t!(fs::write(&stamp, &codegen_backend));
     }
 }
 
@@ -796,8 +796,7 @@ fn copy_codegen_backends_to_sysroot(builder: &Builder,
 
     for backend in builder.config.rust_codegen_backends.iter() {
         let stamp = codegen_backend_stamp(builder, compiler, target, *backend);
-        let mut dylib = String::new();
-        t!(t!(File::open(&stamp)).read_to_string(&mut dylib));
+        let dylib = t!(fs::read_to_string(&stamp));
         let file = Path::new(&dylib);
         let filename = file.file_name().unwrap().to_str().unwrap();
         // change `librustc_codegen_llvm-xxxxxx.so` to `librustc_codegen_llvm-llvm.so`
@@ -1137,10 +1136,7 @@ pub fn run_cargo(builder: &Builder,
     // contents (the list of files to copy) is different or if any dep's mtime
     // is newer then we rewrite the stamp file.
     deps.sort();
-    let mut stamp_contents = Vec::new();
-    if let Ok(mut f) = File::open(stamp) {
-        t!(f.read_to_end(&mut stamp_contents));
-    }
+    let stamp_contents = fs::read(stamp);
     let stamp_mtime = mtime(&stamp);
     let mut new_contents = Vec::new();
     let mut max = None;
@@ -1156,7 +1152,10 @@ pub fn run_cargo(builder: &Builder,
     }
     let max = max.unwrap();
     let max_path = max_path.unwrap();
-    if stamp_contents == new_contents && max <= stamp_mtime {
+    let contents_equal = stamp_contents
+        .map(|contents| contents == new_contents)
+        .unwrap_or_default();
+    if contents_equal && max <= stamp_mtime {
         builder.verbose(&format!("not updating {:?}; contents equal and {:?} <= {:?}",
                 stamp, max, stamp_mtime));
         return deps
@@ -1166,7 +1165,7 @@ pub fn run_cargo(builder: &Builder,
     } else {
         builder.verbose(&format!("updating {:?} as deps changed", stamp));
     }
-    t!(t!(File::create(stamp)).write_all(&new_contents));
+    t!(fs::write(&stamp, &new_contents));
     deps
 }
 

src/bootstrap/config.rs

@@ -15,8 +15,7 @@
 
 use std::collections::{HashMap, HashSet};
 use std::env;
-use std::fs::{self, File};
-use std::io::prelude::*;
+use std::fs;
 use std::path::{Path, PathBuf};
 use std::process;
 use std::cmp;
@@ -416,9 +415,7 @@ impl Config {
         config.run_host_only = !(flags.host.is_empty() && !flags.target.is_empty());
 
         let toml = file.map(|file| {
-            let mut f = t!(File::open(&file));
-            let mut contents = String::new();
-            t!(f.read_to_string(&mut contents));
+            let contents = t!(fs::read_to_string(&file));
             match toml::from_str(&contents) {
                 Ok(table) => table,
                 Err(err) => {

src/bootstrap/dist.rs

@@ -19,8 +19,8 @@
 //! pieces of `rustup.rs`!
 
 use std::env;
-use std::fs::{self, File};
-use std::io::{Read, Write};
+use std::fs;
+use std::io::Write;
 use std::path::{PathBuf, Path};
 use std::process::{Command, Stdio};
 
@@ -1511,8 +1511,7 @@ impl Step for Extended {
         }
 
         let xform = |p: &Path| {
-            let mut contents = String::new();
-            t!(t!(File::open(p)).read_to_string(&mut contents));
+            let mut contents = t!(fs::read_to_string(p));
             if rls_installer.is_none() {
                 contents = filter(&contents, "rls");
             }
@@ -1523,8 +1522,8 @@ impl Step for Extended {
                 contents = filter(&contents, "rustfmt");
             }
             let ret = tmp.join(p.file_name().unwrap());
-            t!(t!(File::create(&ret)).write_all(contents.as_bytes()));
-            return ret
+            t!(fs::write(&ret, &contents));
+            ret
         };
 
         if target.contains("apple-darwin") {
@@ -1869,8 +1868,7 @@ impl Step for HashSign {
         let file = builder.config.dist_gpg_password_file.as_ref().unwrap_or_else(|| {
             panic!("\n\nfailed to specify `dist.gpg-password-file` in `config.toml`\n\n")
         });
-        let mut pass = String::new();
-        t!(t!(File::open(&file)).read_to_string(&mut pass));
+        let pass = t!(fs::read_to_string(&file));
 
         let today = output(Command::new("date").arg("+%Y-%m-%d"));
 

src/bootstrap/doc.rs

@@ -18,8 +18,7 @@
 //! `rustdoc`.
 
 use std::collections::HashSet;
-use std::fs::{self, File};
-use std::io::prelude::*;
+use std::fs;
 use std::io;
 use std::path::{PathBuf, Path};
 
@@ -379,12 +378,11 @@ impl Step for Standalone {
         let version_info = out.join("version_info.html");
 
         if !builder.config.dry_run && !up_to_date(&version_input, &version_info) {
-            let mut info = String::new();
-            t!(t!(File::open(&version_input)).read_to_string(&mut info));
-            let info = info.replace("VERSION", &builder.rust_release())
-                           .replace("SHORT_HASH", builder.rust_info.sha_short().unwrap_or(""))
-                           .replace("STAMP", builder.rust_info.sha().unwrap_or(""));
-            t!(t!(File::create(&version_info)).write_all(info.as_bytes()));
+            let info = t!(fs::read_to_string(&version_input))
+                .replace("VERSION", &builder.rust_release())
+                .replace("SHORT_HASH", builder.rust_info.sha_short().unwrap_or(""))
+                .replace("STAMP", builder.rust_info.sha().unwrap_or(""));
+            t!(fs::write(&version_info, &info));
         }
 
         for file in t!(fs::read_dir(builder.src.join("src/doc"))) {

src/bootstrap/lib.rs

@@ -1067,9 +1067,8 @@ impl Build {
 
     /// Returns the `a.b.c` version that the given package is at.
     fn release_num(&self, package: &str) -> String {
-        let mut toml = String::new();
         let toml_file_name = self.src.join(&format!("src/tools/{}/Cargo.toml", package));
-        t!(t!(File::open(toml_file_name)).read_to_string(&mut toml));
+        let toml = t!(fs::read_to_string(&toml_file_name));
         for line in toml.lines() {
             let prefix = "version = \"";
             let suffix = "\"";
@@ -1151,8 +1150,7 @@ impl Build {
         }
 
         let mut paths = Vec::new();
-        let mut contents = Vec::new();
-        t!(t!(File::open(stamp)).read_to_end(&mut contents));
+        let contents = t!(fs::read(stamp));
         // This is the method we use for extracting paths from the stamp file passed to us. See
         // run_cargo for more information (in compile.rs).
         for part in contents.split(|b| *b == 0) {

src/bootstrap/native.rs

@@ -21,7 +21,6 @@
 use std::env;
 use std::ffi::OsString;
 use std::fs::{self, File};
-use std::io::{Read, Write};
 use std::path::{Path, PathBuf};
 use std::process::Command;
 
@@ -75,8 +74,7 @@ impl Step for Llvm {
         }
 
         let rebuild_trigger = builder.src.join("src/rustllvm/llvm-rebuild-trigger");
-        let mut rebuild_trigger_contents = String::new();
-        t!(t!(File::open(&rebuild_trigger)).read_to_string(&mut rebuild_trigger_contents));
+        let rebuild_trigger_contents = t!(fs::read_to_string(&rebuild_trigger));
 
         let (out_dir, llvm_config_ret_dir) = if emscripten {
             let dir = builder.emscripten_llvm_out(target);
@@ -93,8 +91,7 @@ impl Step for Llvm {
         let build_llvm_config = llvm_config_ret_dir
             .join(exe("llvm-config", &*builder.config.build));
         if done_stamp.exists() {
-            let mut done_contents = String::new();
-            t!(t!(File::open(&done_stamp)).read_to_string(&mut done_contents));
+            let done_contents = t!(fs::read_to_string(&done_stamp));
 
             // If LLVM was already built previously and contents of the rebuild-trigger file
             // didn't change from the previous build, then no action is required.
@@ -261,7 +258,7 @@ impl Step for Llvm {
 
         cfg.build();
 
-        t!(t!(File::create(&done_stamp)).write_all(rebuild_trigger_contents.as_bytes()));
+        t!(fs::write(&done_stamp, &rebuild_trigger_contents));
 
         build_llvm_config
     }

src/bootstrap/sanity.rs

@@ -21,8 +21,7 @@
 use std::collections::HashMap;
 use std::env;
 use std::ffi::{OsString, OsStr};
-use std::fs::{self, File};
-use std::io::Read;
+use std::fs;
 use std::path::PathBuf;
 use std::process::Command;
 
@@ -235,9 +234,7 @@ $ pacman -R cmake && pacman -S mingw-w64-x86_64-cmake
     }
 
     if build.config.channel == "stable" {
-        let mut stage0 = String::new();
-        t!(t!(File::open(build.src.join("src/stage0.txt")))
-            .read_to_string(&mut stage0));
+        let stage0 = t!(fs::read_to_string(build.src.join("src/stage0.txt")));
         if stage0.contains("\ndev:") {
             panic!("bootstrapping from a dev compiler in a stable release, but \
                     should only be bootstrapping from a released compiler!");

src/bootstrap/test.rs

@@ -16,8 +16,7 @@
 use std::env;
 use std::ffi::OsString;
 use std::fmt;
-use std::fs::{self, File};
-use std::io::Read;
+use std::fs;
 use std::iter;
 use std::path::{Path, PathBuf};
 use std::process::Command;
@@ -1427,10 +1426,8 @@ impl Step for ErrorIndex {
 }
 
 fn markdown_test(builder: &Builder, compiler: Compiler, markdown: &Path) -> bool {
-    match File::open(markdown) {
-        Ok(mut file) => {
-            let mut contents = String::new();
-            t!(file.read_to_string(&mut contents));
+    match fs::read_to_string(markdown) {
+        Ok(contents) => {
             if !contents.contains("```") {
                 return true;
             }

src/libcore/convert.rs

@@ -327,7 +327,8 @@ pub trait Into<T>: Sized {
 /// An example usage for error handling:
 ///
 /// ```
-/// use std::io::{self, Read};
+/// use std::fs;
+/// use std::io;
 /// use std::num;
 ///
 /// enum CliError {
@@ -348,9 +349,7 @@ pub trait Into<T>: Sized {
 /// }
 ///
 /// fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
-///     let mut file = std::fs::File::open("test")?;
-///     let mut contents = String::new();
-///     file.read_to_string(&mut contents)?;
+///     let mut contents = fs::read_to_string(&file_name)?;
 ///     let num: i32 = contents.trim().parse()?;
 ///     Ok(num)
 /// }

src/librustc/infer/lexical_region_resolve/graphviz.rs

@@ -31,9 +31,8 @@ use std::borrow::Cow;
 use std::collections::hash_map::Entry::Vacant;
 use std::collections::btree_map::BTreeMap;
 use std::env;
-use std::fs::File;
+use std::fs;
 use std::io;
-use std::io::prelude::*;
 use std::sync::atomic::{AtomicBool, Ordering};
 
 fn print_help_message() {
@@ -268,5 +267,5 @@ fn dump_region_data_to<'a, 'gcx, 'tcx>(region_rels: &RegionRelations<'a, 'gcx, '
     debug!("dump_region_data calling render");
     let mut v = Vec::new();
     dot::render(&g, &mut v).unwrap();
-    File::create(path).and_then(|mut f| f.write_all(&v))
+    fs::write(path, &v)
 }

src/librustc_codegen_utils/codegen_backend.rs

@@ -22,8 +22,8 @@
 #![feature(box_syntax)]
 
 use std::any::Any;
-use std::io::{self, Write};
-use std::fs::File;
+use std::io::Write;
+use std::fs;
 use std::path::Path;
 use std::sync::{mpsc, Arc};
 
@@ -81,11 +81,7 @@ pub struct NoLlvmMetadataLoader;
 
 impl MetadataLoader for NoLlvmMetadataLoader {
     fn get_rlib_metadata(&self, _: &Target, filename: &Path) -> Result<MetadataRef, String> {
-        let mut file = File::open(filename)
-            .map_err(|e| format!("metadata file open err: {:?}", e))?;
-
-        let mut buf = Vec::new();
-        io::copy(&mut file, &mut buf).unwrap();
+        let buf = fs::read(filename).map_err(|e| format!("metadata file open err: {:?}", e))?;
         let buf: OwningRef<Vec<u8>, [u8]> = OwningRef::new(buf);
         Ok(rustc_erase_owner!(buf.map_owner_box()))
     }
@@ -209,8 +205,7 @@ impl CodegenBackend for MetadataOnlyCodegenBackend {
             } else {
                 &ongoing_codegen.metadata.raw_data
             };
-            let mut file = File::create(&output_name).unwrap();
-            file.write_all(metadata).unwrap();
+            fs::write(&output_name, metadata).unwrap();
         }
 
         sess.abort_if_errors();

src/librustdoc/html/render.rs

@@ -778,10 +778,7 @@ fn write_shared(
     let mut themes: FxHashSet<String> = FxHashSet::default();
 
     for entry in &cx.shared.themes {
-        let mut content = Vec::with_capacity(100000);
-
-        let mut f = try_err!(File::open(&entry), &entry);
-        try_err!(f.read_to_end(&mut content), &entry);
+        let content = try_err!(fs::read(&entry), &entry);
         let theme = try_none!(try_none!(entry.file_stem(), &entry).to_str(), &entry);
         let extension = try_none!(try_none!(entry.extension(), &entry).to_str(), &entry);
         write(cx.dst.join(format!("{}{}.{}", theme, cx.shared.resource_suffix, extension)),
@@ -881,10 +878,7 @@ themePicker.onblur = handleThemeButtonsBlur;
         if !options.enable_minification {
             try_err!(fs::copy(css, out), css);
         } else {
-            let mut f = try_err!(File::open(css), css);
-            let mut buffer = String::with_capacity(1000);
-
-            try_err!(f.read_to_string(&mut buffer), css);
+            let buffer = try_err!(fs::read_to_string(css), css);
             write_minify(out, &buffer, options.enable_minification)?;
         }
     }
@@ -2102,8 +2096,7 @@ impl Context {
                 if !buf.is_empty() {
                     try_err!(this.shared.ensure_dir(&this.dst), &this.dst);
                     let joint_dst = this.dst.join("index.html");
-                    let mut dst = try_err!(File::create(&joint_dst), &joint_dst);
-                    try_err!(dst.write_all(&buf), &joint_dst);
+                    try_err!(fs::write(&joint_dst, buf), &joint_dst);
                 }
 
                 let m = match item.inner {
@@ -2137,8 +2130,7 @@ impl Context {
                 let file_name = &item_path(item_type, name);
                 try_err!(self.shared.ensure_dir(&self.dst), &self.dst);
                 let joint_dst = self.dst.join(file_name);
-                let mut dst = try_err!(File::create(&joint_dst), &joint_dst);
-                try_err!(dst.write_all(&buf), &joint_dst);
+                try_err!(fs::write(&joint_dst, buf), &joint_dst);
 
                 if !self.render_redirect_pages {
                     all.append(full_path(self, &item), &item_type);

src/librustdoc/theme.rs

@@ -9,9 +9,8 @@
 // except according to those terms.
 
 use rustc_data_structures::fx::FxHashSet;
-use std::fs::File;
+use std::fs;
 use std::hash::{Hash, Hasher};
-use std::io::Read;
 use std::path::Path;
 
 use errors::Handler;
@@ -278,12 +277,9 @@ pub fn get_differences(against: &CssPath, other: &CssPath, v: &mut Vec<String>)
 pub fn test_theme_against<P: AsRef<Path>>(f: &P, against: &CssPath, diag: &Handler)
     -> (bool, Vec<String>)
 {
-    let mut file = try_something!(File::open(f), diag, (false, Vec::new()));
-    let mut data = Vec::with_capacity(1000);
-
-    try_something!(file.read_to_end(&mut data), diag, (false, Vec::new()));
+    let data = try_something!(fs::read(f), diag, (false, vec![]));
     let paths = load_css_paths(&data);
-    let mut ret = Vec::new();
+    let mut ret = vec![];
     get_differences(against, &paths, &mut ret);
     (true, ret)
 }