Auto merge of #56258 - euclio:fs-read-write, r=euclio

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.

8 files changed, 33 insertions, 52 deletions

diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index b6bb11d07ef..2e792b6053e 100644
--- a/src/bootstrap/compile.rs
+++ b/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
 }
 
diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index 8fc2d5787cb..1dafbe148af 100644
--- a/src/bootstrap/config.rs
+++ b/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) => {
diff --git a/src/bootstrap/dist.rs b/src/bootstrap/dist.rs
index 6108692e43c..d9ff6276d52 100644
--- a/src/bootstrap/dist.rs
+++ b/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"));
 
diff --git a/src/bootstrap/doc.rs b/src/bootstrap/doc.rs
index e9c27a3f3cf..2d0625b26db 100644
--- a/src/bootstrap/doc.rs
+++ b/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"))) {
diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index 2832f5bebdd..a62830da4bb 100644
--- a/src/bootstrap/lib.rs
+++ b/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) {
diff --git a/src/bootstrap/native.rs b/src/bootstrap/native.rs
index 448967ef0c2..150b6bea180 100644
--- a/src/bootstrap/native.rs
+++ b/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
     }
diff --git a/src/bootstrap/sanity.rs b/src/bootstrap/sanity.rs
index 15d3bccba09..7a9e6d4fd38 100644
--- a/src/bootstrap/sanity.rs
+++ b/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!");
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index da827356800..4ece3435e92 100644
--- a/src/bootstrap/test.rs
+++ b/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;
             }