Auto merge of rust-lang#130803 - cuviper:file-buffered, r=joshtriplett

Add `File` constructors that return files wrapped with a buffer

In addition to the light convenience, these are intended to raise visibility that buffering is something you should consider when opening a file, since unbuffered I/O is a common performance footgun to Rust newcomers.

ACP: rust-lang/libs-team#446
Tracking Issue: rust-lang#130804

compiler/rustc_borrowck/src/facts.rs

@@ -1,7 +1,7 @@
 use std::error::Error;
 use std::fmt::Debug;
 use std::fs::{self, File};
-use std::io::{BufWriter, Write};
+use std::io::Write;
 use std::path::Path;
 
 use polonius_engine::{AllFacts as PoloniusFacts, Atom};
@@ -127,7 +127,7 @@ impl<'w> FactWriter<'w> {
  T: FactRow,
  {
  let file = &self.dir.join(file_name);
- let mut file = BufWriter::new(File::create(file)?);
+ let mut file = File::create_buffered(file)?;
  for row in rows {
  row.write(&mut file, self.location_table)?;
  }

compiler/rustc_borrowck/src/lib.rs

@@ -6,6 +6,7 @@
 #![feature(assert_matches)]
 #![feature(box_patterns)]
 #![feature(control_flow_enum)]
+#![feature(file_buffered)]
 #![feature(let_chains)]
 #![feature(never_type)]
 #![feature(rustc_attrs)]

compiler/rustc_codegen_llvm/src/back/lto.rs

@@ -808,8 +808,7 @@ struct ThinLTOKeysMap {
 impl ThinLTOKeysMap {
  fn save_to_file(&self, path: &Path) -> io::Result<()> {
  use std::io::Write;
- let file = File::create(path)?;
- let mut writer = io::BufWriter::new(file);
+ let mut writer = File::create_buffered(path)?;
  // The entries are loaded back into a hash map in `load_from_file()`, so
  // the order in which we write them to file here does not matter.
  for (module, key) in &self.keys {
@@ -821,8 +820,8 @@ impl ThinLTOKeysMap {
  fn load_from_file(path: &Path) -> io::Result<Self> {
  use std::io::BufRead;
  let mut keys = BTreeMap::default();
- let file = File::open(path)?;
- for line in io::BufReader::new(file).lines() {
+ let file = File::open_buffered(path)?;
+ for line in file.lines() {
  let line = line?;
  let mut split = line.split(' ');
  let module = split.next().unwrap();

compiler/rustc_codegen_llvm/src/lib.rs

@@ -11,6 +11,7 @@
 #![feature(assert_matches)]
 #![feature(exact_size_is_empty)]
 #![feature(extern_types)]
+#![feature(file_buffered)]
 #![feature(hash_raw_entry)]
 #![feature(impl_trait_in_assoc_type)]
 #![feature(iter_intersperse)]

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -1,9 +1,8 @@
 use std::ffi::{OsStr, OsString};
 use std::fs::{self, File};
 use std::io::prelude::*;
-use std::io::{self, BufWriter};
 use std::path::{Path, PathBuf};
-use std::{env, iter, mem, str};
+use std::{env, io, iter, mem, str};
 
 use cc::windows_registry;
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
@@ -754,7 +753,7 @@ impl<'a> Linker for GccLinker<'a> {
  if self.sess.target.is_like_osx {
  // Write a plain, newline-separated list of symbols
  let res: io::Result<()> = try {
- let mut f = BufWriter::new(File::create(&path)?);
+ let mut f = File::create_buffered(&path)?;
  for sym in symbols {
  debug!(" _{sym}");
  writeln!(f, "_{sym}")?;
@@ -765,7 +764,7 @@ impl<'a> Linker for GccLinker<'a> {
  }
  } else if is_windows {
  let res: io::Result<()> = try {
- let mut f = BufWriter::new(File::create(&path)?);
+ let mut f = File::create_buffered(&path)?;
 
  // .def file similar to MSVC one but without LIBRARY section
  // because LD doesn't like when it's empty
@@ -781,7 +780,7 @@ impl<'a> Linker for GccLinker<'a> {
  } else {
  // Write an LD version script
  let res: io::Result<()> = try {
- let mut f = BufWriter::new(File::create(&path)?);
+ let mut f = File::create_buffered(&path)?;
  writeln!(f, "{{")?;
  if !symbols.is_empty() {
  writeln!(f, " global:")?;
@@ -1059,7 +1058,7 @@ impl<'a> Linker for MsvcLinker<'a> {
 
  let path = tmpdir.join("lib.def");
  let res: io::Result<()> = try {
- let mut f = BufWriter::new(File::create(&path)?);
+ let mut f = File::create_buffered(&path)?;
 
  // Start off with the standard module name header and then go
  // straight to exports.
@@ -1648,7 +1647,7 @@ impl<'a> Linker for AixLinker<'a> {
  fn export_symbols(&mut self, tmpdir: &Path, _crate_type: CrateType, symbols: &[String]) {
  let path = tmpdir.join("list.exp");
  let res: io::Result<()> = try {
- let mut f = BufWriter::new(File::create(&path)?);
+ let mut f = File::create_buffered(&path)?;
  // FIXME: use llvm-nm to generate export list.
  for symbol in symbols {
  debug!(" _{symbol}");
@@ -1961,7 +1960,7 @@ impl<'a> Linker for BpfLinker<'a> {
  fn export_symbols(&mut self, tmpdir: &Path, _crate_type: CrateType, symbols: &[String]) {
  let path = tmpdir.join("symbols");
  let res: io::Result<()> = try {
- let mut f = BufWriter::new(File::create(&path)?);
+ let mut f = File::create_buffered(&path)?;
  for sym in symbols {
  writeln!(f, "{sym}")?;
  }

compiler/rustc_codegen_ssa/src/lib.rs

@@ -6,6 +6,7 @@
 #![doc(rust_logo)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
+#![feature(file_buffered)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
 #![feature(negative_impls)]

compiler/rustc_data_structures/src/lib.rs

@@ -23,6 +23,7 @@
 #![feature(cfg_match)]
 #![feature(core_intrinsics)]
 #![feature(extend_one)]
+#![feature(file_buffered)]
 #![feature(hash_raw_entry)]
 #![feature(macro_metavar_expr)]
 #![feature(map_try_insert)]

compiler/rustc_data_structures/src/obligation_forest/graphviz.rs

@@ -1,6 +1,5 @@
 use std::env::var_os;
 use std::fs::File;
-use std::io::BufWriter;
 use std::path::Path;
 use std::sync::atomic::{AtomicUsize, Ordering};
 
@@ -33,7 +32,7 @@ impl<O: ForestObligation> ObligationForest<O> {
 
  let file_path = dir.as_ref().join(format!("{counter:010}_{description}.gv"));
 
- let mut gv_file = BufWriter::new(File::create(file_path).unwrap());
+ let mut gv_file = File::create_buffered(file_path).unwrap();
 
  dot::render(&self, &mut gv_file).unwrap();
  }

compiler/rustc_incremental/src/assert_dep_graph.rs

@@ -35,7 +35,7 @@
 
 use std::env;
 use std::fs::{self, File};
-use std::io::{BufWriter, Write};
+use std::io::Write;
 
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_data_structures::graph::implementation::{Direction, INCOMING, NodeIndex, OUTGOING};
@@ -245,7 +245,7 @@ fn dump_graph(query: &DepGraphQuery) {
  {
  // dump a .txt file with just the edges:
  let txt_path = format!("{path}.txt");
- let mut file = BufWriter::new(File::create(&txt_path).unwrap());
+ let mut file = File::create_buffered(&txt_path).unwrap();
  for (source, target) in &edges {
  write!(file, "{source:?} -> {target:?}\n").unwrap();
  }

compiler/rustc_incremental/src/lib.rs

@@ -5,6 +5,7 @@
 #![deny(missing_docs)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
+#![feature(file_buffered)]
 #![feature(rustdoc_internals)]
 #![warn(unreachable_pub)]
 // tidy-alphabetical-end

compiler/rustc_interface/src/lib.rs

@@ -1,5 +1,6 @@
 // tidy-alphabetical-start
 #![feature(decl_macro)]
+#![feature(file_buffered)]
 #![feature(let_chains)]
 #![feature(try_blocks)]
 #![warn(unreachable_pub)]

compiler/rustc_interface/src/passes.rs

@@ -519,7 +519,7 @@ fn write_out_deps(tcx: TyCtxt<'_>, outputs: &OutputFilenames, out_filenames: &[P
  write_deps_to_file(&mut file)?;
  }
  OutFileName::Real(ref path) => {
- let mut file = BufWriter::new(fs::File::create(path)?);
+ let mut file = fs::File::create_buffered(path)?;
  write_deps_to_file(&mut file)?;
  }
  }

compiler/rustc_metadata/src/fs.rs

@@ -128,8 +128,7 @@ pub fn non_durable_rename(src: &Path, dst: &Path) -> std::io::Result<()> {
 }
 
 pub fn copy_to_stdout(from: &Path) -> io::Result<()> {
- let file = fs::File::open(from)?;
- let mut reader = io::BufReader::new(file);
+ let mut reader = fs::File::open_buffered(from)?;
  let mut stdout = io::stdout();
  io::copy(&mut reader, &mut stdout)?;
  Ok(())

compiler/rustc_metadata/src/lib.rs

@@ -8,6 +8,7 @@
 #![feature(decl_macro)]
 #![feature(error_iter)]
 #![feature(extract_if)]
+#![feature(file_buffered)]
 #![feature(if_let_guard)]
 #![feature(iter_from_coroutine)]
 #![feature(let_chains)]

compiler/rustc_middle/src/lib.rs

@@ -45,6 +45,7 @@
 #![feature(discriminant_kind)]
 #![feature(extern_types)]
 #![feature(extract_if)]
+#![feature(file_buffered)]
 #![feature(if_let_guard)]
 #![feature(intra_doc_pointers)]
 #![feature(iter_from_coroutine)]

compiler/rustc_middle/src/mir/pretty.rs

@@ -277,9 +277,9 @@ pub fn create_dump_file<'tcx>(
  )
  })?;
  }
- Ok(io::BufWriter::new(fs::File::create(&file_path).map_err(|e| {
+ Ok(fs::File::create_buffered(&file_path).map_err(|e| {
  io::Error::new(e.kind(), format!("IO error creating MIR dump file: {file_path:?}; {e}"))
- })?))
+ })?)
 }
 
 ///////////////////////////////////////////////////////////////////////////

compiler/rustc_mir_dataflow/src/framework/engine.rs

@@ -266,7 +266,7 @@ where
  A::Domain: DebugWithContext<A>,
 {
  use std::fs;
- use std::io::{self, Write};
+ use std::io::Write;
 
  let def_id = body.source.def_id();
  let Ok(attrs) = RustcMirAttrs::parse(tcx, def_id) else {
@@ -281,8 +281,7 @@ where
  if let Some(parent) = path.parent() {
  fs::create_dir_all(parent)?;
  }
- let f = fs::File::create(&path)?;
- io::BufWriter::new(f)
+ fs::File::create_buffered(&path)?
  }
 
  None if dump_enabled(tcx, A::NAME, def_id) => {

compiler/rustc_mir_dataflow/src/lib.rs

@@ -3,6 +3,7 @@
 #![feature(associated_type_defaults)]
 #![feature(box_patterns)]
 #![feature(exact_size_is_empty)]
+#![feature(file_buffered)]
 #![feature(let_chains)]
 #![feature(try_blocks)]
 #![warn(unreachable_pub)]

compiler/rustc_mir_transform/src/dump_mir.rs

@@ -24,7 +24,7 @@ pub fn emit_mir(tcx: TyCtxt<'_>) -> io::Result<()> {
  write_mir_pretty(tcx, None, &mut f)?;
  }
  OutFileName::Real(path) => {
- let mut f = io::BufWriter::new(File::create(&path)?);
+ let mut f = File::create_buffered(&path)?;
  write_mir_pretty(tcx, None, &mut f)?;
  if tcx.sess.opts.json_artifact_notifications {
  tcx.dcx().emit_artifact_notification(&path, "mir");

compiler/rustc_mir_transform/src/lib.rs

@@ -3,6 +3,7 @@
 #![feature(box_patterns)]
 #![feature(const_type_name)]
 #![feature(cow_is_borrowed)]
+#![feature(file_buffered)]
 #![feature(if_let_guard)]
 #![feature(impl_trait_in_assoc_type)]
 #![feature(let_chains)]

compiler/rustc_monomorphize/src/lib.rs

@@ -1,5 +1,6 @@
 // tidy-alphabetical-start
 #![feature(array_windows)]
+#![feature(file_buffered)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
 #![warn(unreachable_pub)]

compiler/rustc_monomorphize/src/partitioning.rs

@@ -95,7 +95,7 @@
 use std::cmp;
 use std::collections::hash_map::Entry;
 use std::fs::{self, File};
-use std::io::{BufWriter, Write};
+use std::io::Write;
 use std::path::{Path, PathBuf};
 
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
@@ -1243,8 +1243,7 @@ fn dump_mono_items_stats<'tcx>(
  let ext = format.extension();
  let filename = format!("{crate_name}.mono_items.{ext}");
  let output_path = output_directory.join(&filename);
- let file = File::create(&output_path)?;
- let mut file = BufWriter::new(file);
+ let mut file = File::create_buffered(&output_path)?;
 
  // Gather instantiated mono items grouped by def_id
  let mut items_per_def_id: FxIndexMap<_, Vec<_>> = Default::default();

library/std/src/fs.rs

@@ -375,6 +375,44 @@ impl File {
  OpenOptions::new().read(true).open(path.as_ref())
  }
 
+ /// Attempts to open a file in read-only mode with buffering.
+ ///
+ /// See the [`OpenOptions::open`] method, the [`BufReader`][io::BufReader] type,
+ /// and the [`BufRead`][io::BufRead] trait for more details.
+ ///
+ /// If you only need to read the entire file contents,
+ /// consider [`std::fs::read()`][self::read] or
+ /// [`std::fs::read_to_string()`][self::read_to_string] instead.
+ ///
+ /// # Errors
+ ///
+ /// This function will return an error if `path` does not already exist.
+ /// Other errors may also be returned according to [`OpenOptions::open`].
+ ///
+ /// # Examples
+ ///
+ /// ```no_run
+ /// #![feature(file_buffered)]
+ /// use std::fs::File;
+ /// use std::io::BufRead;
+ ///
+ /// fn main() -> std::io::Result<()> {
+ /// let mut f = File::open_buffered("foo.txt")?;
+ /// assert!(f.capacity() > 0);
+ /// for (line, i) in f.lines().zip(1..) {
+ /// println!("{i:6}: {}", line?);
+ /// }
+ /// Ok(())
+ /// }
+ /// ```
+ #[unstable(feature = "file_buffered", issue = "130804")]
+ pub fn open_buffered<P: AsRef<Path>>(path: P) -> io::Result<io::BufReader<File>> {
+ // Allocate the buffer *first* so we don't affect the filesystem otherwise.
+ let buffer = io::BufReader::<Self>::try_new_buffer()?;
+ let file = File::open(path)?;
+ Ok(io::BufReader::with_buffer(file, buffer))
+ }
+
  /// Opens a file in write-only mode.
  ///
  /// This function will create a file if it does not exist,
@@ -404,6 +442,45 @@ impl File {
  OpenOptions::new().write(true).create(true).truncate(true).open(path.as_ref())
  }
 
+ /// Opens a file in write-only mode with buffering.
+ ///
+ /// This function will create a file if it does not exist,
+ /// and will truncate it if it does.
+ ///
+ /// Depending on the platform, this function may fail if the
+ /// full directory path does not exist.
+ ///
+ /// See the [`OpenOptions::open`] method and the
+ /// [`BufWriter`][io::BufWriter] type for more details.
+ ///
+ /// See also [`std::fs::write()`][self::write] for a simple function to
+ /// create a file with some given data.
+ ///
+ /// # Examples
+ ///
+ /// ```no_run
+ /// #![feature(file_buffered)]
+ /// use std::fs::File;
+ /// use std::io::Write;
+ ///
+ /// fn main() -> std::io::Result<()> {
+ /// let mut f = File::create_buffered("foo.txt")?;
+ /// assert!(f.capacity() > 0);
+ /// for i in 0..100 {
+ /// writeln!(&mut f, "{i}")?;
+ /// }
+ /// f.flush()?;
+ /// Ok(())
+ /// }
+ /// ```
+ #[unstable(feature = "file_buffered", issue = "130804")]
+ pub fn create_buffered<P: AsRef<Path>>(path: P) -> io::Result<io::BufWriter<File>> {
+ // Allocate the buffer *first* so we don't affect the filesystem otherwise.
+ let buffer = io::BufWriter::<Self>::try_new_buffer()?;
+ let file = File::create(path)?;
+ Ok(io::BufWriter::with_buffer(file, buffer))
+ }
+
  /// Creates a new file in read-write mode; error if the file exists.
  ///
  /// This function will create a file if it does not exist, or return an error if it does. This