src/cmd/gofmt/gofmt.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package main

 import (
 	"bytes"
 	"context"
 	"flag"
 	"fmt"
 	"go/ast"
 	"go/parser"
 	"go/printer"
 	"go/scanner"
 	"go/token"
 	"internal/diff"
 	"io"
 	"io/fs"
 	"os"
 	"path/filepath"
 	"runtime"
 	"runtime/pprof"
 	"strings"

 	"golang.org/x/sync/semaphore"
 )

 var (
 	// main operation modes
 	list        = flag.Bool("l", false, "list files whose formatting differs from gofmt's")
 	write       = flag.Bool("w", false, "write result to (source) file instead of stdout")
 	rewriteRule = flag.String("r", "", "rewrite rule (e.g., 'a[b:len(a)] -> a[b:]')")
 	simplifyAST = flag.Bool("s", false, "simplify code")
 	doDiff      = flag.Bool("d", false, "display diffs instead of rewriting files")
 	allErrors   = flag.Bool("e", false, "report all errors (not just the first 10 on different lines)")

 	// debugging
 	cpuprofile = flag.String("cpuprofile", "", "write cpu profile to this file")
 )

 // Keep these in sync with go/format/format.go.
 const (
 	tabWidth    = 8
 	printerMode = printer.UseSpaces | printer.TabIndent | printerNormalizeNumbers

 	// printerNormalizeNumbers means to canonicalize number literal prefixes
 	// and exponents while printing. See https://golang.org/doc/go1.13#gofmt.
 	//
 	// This value is defined in go/printer specifically for go/format and cmd/gofmt.
 	printerNormalizeNumbers = 1 << 30
 )

 // fdSem guards the number of concurrently-open file descriptors.
 //
 // For now, this is arbitrarily set to 200, based on the observation that many
 // platforms default to a kernel limit of 256. Ideally, perhaps we should derive
 // it from rlimit on platforms that support that system call.
 //
 // File descriptors opened from outside of this package are not tracked,
 // so this limit may be approximate.
 var fdSem = make(chan bool, 200)

 var (
 	rewrite    func(*token.FileSet, *ast.File) *ast.File
 	parserMode parser.Mode
 )

 func usage() {
 	fmt.Fprintf(os.Stderr, "usage: gofmt [flags] [path ...]\n")
 	flag.PrintDefaults()
 }

 func initParserMode() {
 	parserMode = parser.ParseComments
 	if *allErrors {
 		parserMode |= parser.AllErrors
 	}
 	// It's only -r that makes use of go/ast's object resolution,
 	// so avoid the unnecessary work if the flag isn't used.
 	if *rewriteRule == "" {
 		parserMode |= parser.SkipObjectResolution
 	}
 }

 func isGoFile(f fs.DirEntry) bool {
 	// ignore non-Go files
 	name := f.Name()
 	return !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".go") && !f.IsDir()
 }

 // A sequencer performs concurrent tasks that may write output, but emits that
 // output in a deterministic order.
 type sequencer struct {
 	maxWeight int64
 	sem       *semaphore.Weighted   // weighted by input bytes (an approximate proxy for memory overhead)
 	prev      <-chan *reporterState // 1-buffered
 }

 // newSequencer returns a sequencer that allows concurrent tasks up to maxWeight
 // and writes tasks' output to out and err.
 func newSequencer(maxWeight int64, out, err io.Writer) *sequencer {
 	sem := semaphore.NewWeighted(maxWeight)
 	prev := make(chan *reporterState, 1)
 	prev <- &reporterState{out: out, err: err}
 	return &sequencer{
 		maxWeight: maxWeight,
 		sem:       sem,
 		prev:      prev,
 	}
 }

 // exclusive is a weight that can be passed to a sequencer to cause
 // a task to be executed without any other concurrent tasks.
 const exclusive = -1

 // Add blocks until the sequencer has enough weight to spare, then adds f as a
 // task to be executed concurrently.
 //
 // If the weight is either negative or larger than the sequencer's maximum
 // weight, Add blocks until all other tasks have completed, then the task
 // executes exclusively (blocking all other calls to Add until it completes).
 //
 // f may run concurrently in a goroutine, but its output to the passed-in
 // reporter will be sequential relative to the other tasks in the sequencer.
 //
 // If f invokes a method on the reporter, execution of that method may block
 // until the previous task has finished. (To maximize concurrency, f should
 // avoid invoking the reporter until it has finished any parallelizable work.)
 //
 // If f returns a non-nil error, that error will be reported after f's output
 // (if any) and will cause a nonzero final exit code.
 func (s *sequencer) Add(weight int64, f func(*reporter) error) {
 	if weight < 0 || weight > s.maxWeight {
 		weight = s.maxWeight
 	}
 	if err := s.sem.Acquire(context.TODO(), weight); err != nil {
 		// Change the task from "execute f" to "report err".
 		weight = 0
 		f = func(*reporter) error { return err }
 	}

 	r := &reporter{prev: s.prev}
 	next := make(chan *reporterState, 1)
 	s.prev = next

 	// Start f in parallel: it can run until it invokes a method on r, at which
 	// point it will block until the previous task releases the output state.
 	go func() {
 		if err := f(r); err != nil {
 			r.Report(err)
 		}
 		next <- r.getState() // Release the next task.
 		s.sem.Release(weight)
 	}()
 }

 // AddReport prints an error to s after the output of any previously-added
 // tasks, causing the final exit code to be nonzero.
 func (s *sequencer) AddReport(err error) {
 	s.Add(0, func(*reporter) error { return err })
 }

 // GetExitCode waits for all previously-added tasks to complete, then returns an
 // exit code for the sequence suitable for passing to os.Exit.
 func (s *sequencer) GetExitCode() int {
 	c := make(chan int, 1)
 	s.Add(0, func(r *reporter) error {
 		c <- r.ExitCode()
 		return nil
 	})
 	return <-c
 }

 // A reporter reports output, warnings, and errors.
 type reporter struct {
 	prev  <-chan *reporterState
 	state *reporterState
 }

 // reporterState carries the state of a reporter instance.
 //
 // Only one reporter at a time may have access to a reporterState.
 type reporterState struct {
 	out, err io.Writer
 	exitCode int
 }

 // getState blocks until any prior reporters are finished with the reporter
 // state, then returns the state for manipulation.
 func (r *reporter) getState() *reporterState {
 	if r.state == nil {
 		r.state = <-r.prev
 	}
 	return r.state
 }

 // Warnf emits a warning message to the reporter's error stream,
 // without changing its exit code.
 func (r *reporter) Warnf(format string, args ...any) {
 	fmt.Fprintf(r.getState().err, format, args...)
 }

 // Write emits a slice to the reporter's output stream.
 //
 // Any error is returned to the caller, and does not otherwise affect the
 // reporter's exit code.
 func (r *reporter) Write(p []byte) (int, error) {
 	return r.getState().out.Write(p)
 }

 // Report emits a non-nil error to the reporter's error stream,
 // changing its exit code to a nonzero value.
 func (r *reporter) Report(err error) {
 	if err == nil {
 		panic("Report with nil error")
 	}
 	st := r.getState()
 	scanner.PrintError(st.err, err)
 	st.exitCode = 2
 }

 func (r *reporter) ExitCode() int {
 	return r.getState().exitCode
 }

 // If info == nil, we are formatting stdin instead of a file.
 // If in == nil, the source is the contents of the file with the given filename.
 func processFile(filename string, info fs.FileInfo, in io.Reader, r *reporter) error {
 	src, err := readFile(filename, info, in)
 	if err != nil {
 		return err
 	}

 	fileSet := token.NewFileSet()
 	fragmentOk := false
 	if info == nil {
 		// If we are formatting stdin, we accept a program fragment in lieu of a
 		// complete source file.
 		fragmentOk = true
 	}
 	file, sourceAdj, indentAdj, err := parse(fileSet, filename, src, fragmentOk)
 	if err != nil {
 		return err
 	}

 	if rewrite != nil {
 		if sourceAdj == nil {
 			file = rewrite(fileSet, file)
 		} else {
 			r.Warnf("warning: rewrite ignored for incomplete programs\n")
 		}
 	}

 	ast.SortImports(fileSet, file)

 	if *simplifyAST {
 		simplify(file)
 	}

 	res, err := format(fileSet, file, sourceAdj, indentAdj, src, printer.Config{Mode: printerMode, Tabwidth: tabWidth})
 	if err != nil {
 		return err
 	}

 	if !bytes.Equal(src, res) {
 		// formatting has changed
 		if *list {
 			fmt.Fprintln(r, filename)
 		}
 		if *write {
 			if info == nil {
 				panic("-w should not have been allowed with stdin")
 			}
 			// make a temporary backup before overwriting original
 			perm := info.Mode().Perm()
 			bakname, err := backupFile(filename+".", src, perm)
 			if err != nil {
 				return err
 			}
 			fdSem <- true
 			err = os.WriteFile(filename, res, perm)
 			<-fdSem
 			if err != nil {
 				os.Rename(bakname, filename)
 				return err
 			}
 			err = os.Remove(bakname)
 			if err != nil {
 				return err
 			}
 		}
 		if *doDiff {
 			newName := filepath.ToSlash(filename)
 			oldName := newName + ".orig"
 			r.Write(diff.Diff(oldName, src, newName, res))
 		}
 	}

 	if !*list && !*write && !*doDiff {
 		_, err = r.Write(res)
 	}

 	return err
 }

 // readFile reads the contents of filename, described by info.
 // If in is non-nil, readFile reads directly from it.
 // Otherwise, readFile opens and reads the file itself,
 // with the number of concurrently-open files limited by fdSem.
 func readFile(filename string, info fs.FileInfo, in io.Reader) ([]byte, error) {
 	if in == nil {
 		fdSem <- true
 		var err error
 		f, err := os.Open(filename)
 		if err != nil {
 			return nil, err
 		}
 		in = f
 		defer func() {
 			f.Close()
 			<-fdSem
 		}()
 	}

 	// Compute the file's size and read its contents with minimal allocations.
 	//
 	// If we have the FileInfo from filepath.WalkDir, use it to make
 	// a buffer of the right size and avoid ReadAll's reallocations.
 	//
 	// If the size is unknown (or bogus, or overflows an int), fall back to
 	// a size-independent ReadAll.
 	size := -1
 	if info != nil && info.Mode().IsRegular() && int64(int(info.Size())) == info.Size() {
 		size = int(info.Size())
 	}
 	if size+1 <= 0 {
 		// The file is not known to be regular, so we don't have a reliable size for it.
 		var err error
 		src, err := io.ReadAll(in)
 		if err != nil {
 			return nil, err
 		}
 		return src, nil
 	}

 	// We try to read size+1 bytes so that we can detect modifications: if we
 	// read more than size bytes, then the file was modified concurrently.
 	// (If that happens, we could, say, append to src to finish the read, or
 	// proceed with a truncated buffer — but the fact that it changed at all
 	// indicates a possible race with someone editing the file, so we prefer to
 	// stop to avoid corrupting it.)
 	src := make([]byte, size+1)
 	n, err := io.ReadFull(in, src)
 	switch err {
 	case nil, io.EOF, io.ErrUnexpectedEOF:
 		// io.ReadFull returns io.EOF (for an empty file) or io.ErrUnexpectedEOF
 		// (for a non-empty file) if the file was changed unexpectedly. Continue
 		// with comparing file sizes in those cases.
 	default:
 		return nil, err
 	}
 	if n < size {
 		return nil, fmt.Errorf("error: size of %s changed during reading (from %d to %d bytes)", filename, size, n)
 	} else if n > size {
 		return nil, fmt.Errorf("error: size of %s changed during reading (from %d to >=%d bytes)", filename, size, len(src))
 	}
 	return src[:n], nil
 }

 func main() {
 	// Arbitrarily limit in-flight work to 2MiB times the number of threads.
 	//
 	// The actual overhead for the parse tree and output will depend on the
 	// specifics of the file, but this at least keeps the footprint of the process
 	// roughly proportional to GOMAXPROCS.
 	maxWeight := (2 << 20) * int64(runtime.GOMAXPROCS(0))
 	s := newSequencer(maxWeight, os.Stdout, os.Stderr)

 	// call gofmtMain in a separate function
 	// so that it can use defer and have them
 	// run before the exit.
 	gofmtMain(s)
 	os.Exit(s.GetExitCode())
 }

 func gofmtMain(s *sequencer) {
 	flag.Usage = usage
 	flag.Parse()

 	if *cpuprofile != "" {
 		fdSem <- true
 		f, err := os.Create(*cpuprofile)
 		if err != nil {
 			s.AddReport(fmt.Errorf("creating cpu profile: %s", err))
 			return
 		}
 		defer func() {
 			f.Close()
 			<-fdSem
 		}()
 		pprof.StartCPUProfile(f)
 		defer pprof.StopCPUProfile()
 	}

 	initParserMode()
 	initRewrite()

 	args := flag.Args()
 	if len(args) == 0 {
 		if *write {
 			s.AddReport(fmt.Errorf("error: cannot use -w with standard input"))
 			return
 		}
 		s.Add(0, func(r *reporter) error {
 			return processFile("<standard input>", nil, os.Stdin, r)
 		})
 		return
 	}

 	for _, arg := range args {
 		switch info, err := os.Stat(arg); {
 		case err != nil:
 			s.AddReport(err)
 		case !info.IsDir():
 			// Non-directory arguments are always formatted.
 			arg := arg
 			s.Add(fileWeight(arg, info), func(r *reporter) error {
 				return processFile(arg, info, nil, r)
 			})
 		default:
 			// Directories are walked, ignoring non-Go files.
 			err := filepath.WalkDir(arg, func(path string, f fs.DirEntry, err error) error {
 				if err != nil || !isGoFile(f) {
 					return err
 				}
 				info, err := f.Info()
 				if err != nil {
 					s.AddReport(err)
 					return nil
 				}
 				s.Add(fileWeight(path, info), func(r *reporter) error {
 					return processFile(path, info, nil, r)
 				})
 				return nil
 			})
 			if err != nil {
 				s.AddReport(err)
 			}
 		}
 	}
 }

 func fileWeight(path string, info fs.FileInfo) int64 {
 	if info == nil {
 		return exclusive
 	}
 	if info.Mode().Type() == fs.ModeSymlink {
 		var err error
 		info, err = os.Stat(path)
 		if err != nil {
 			return exclusive
 		}
 	}
 	if !info.Mode().IsRegular() {
 		// For non-regular files, FileInfo.Size is system-dependent and thus not a
 		// reliable indicator of weight.
 		return exclusive
 	}
 	return info.Size()
 }

 const chmodSupported = runtime.GOOS != "windows"

 // backupFile writes data to a new file named filename<number> with permissions perm,
 // with <number randomly chosen such that the file name is unique. backupFile returns
 // the chosen file name.
 func backupFile(filename string, data []byte, perm fs.FileMode) (string, error) {
 	fdSem <- true
 	defer func() { <-fdSem }()

 	// create backup file
 	f, err := os.CreateTemp(filepath.Dir(filename), filepath.Base(filename))
 	if err != nil {
 		return "", err
 	}
 	bakname := f.Name()
 	if chmodSupported {
 		err = f.Chmod(perm)
 		if err != nil {
 			f.Close()
 			os.Remove(bakname)
 			return bakname, err
 		}
 	}

 	// write data to backup file
 	_, err = f.Write(data)
 	if err1 := f.Close(); err == nil {
 		err = err1
 	}

 	return bakname, err
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package main

	import (
	"bytes"
	"context"
	"flag"
	"fmt"
	"go/ast"
	"go/parser"
	"go/printer"
	"go/scanner"
	"go/token"
	"internal/diff"
	"io"
	"io/fs"
	"os"
	"path/filepath"
	"runtime"
	"runtime/pprof"
	"strings"

	"golang.org/x/sync/semaphore"
	)

	var (
	// main operation modes
	list = flag.Bool("l", false, "list files whose formatting differs from gofmt's")
	write = flag.Bool("w", false, "write result to (source) file instead of stdout")
	rewriteRule = flag.String("r", "", "rewrite rule (e.g., 'a[b:len(a)] -> a[b:]')")
	simplifyAST = flag.Bool("s", false, "simplify code")
	doDiff = flag.Bool("d", false, "display diffs instead of rewriting files")
	allErrors = flag.Bool("e", false, "report all errors (not just the first 10 on different lines)")

	// debugging
	cpuprofile = flag.String("cpuprofile", "", "write cpu profile to this file")
	)

	// Keep these in sync with go/format/format.go.
	const (
	tabWidth = 8
	printerMode = printer.UseSpaces \| printer.TabIndent \| printerNormalizeNumbers

	// printerNormalizeNumbers means to canonicalize number literal prefixes
	// and exponents while printing. See https://golang.org/doc/go1.13#gofmt.
	//
	// This value is defined in go/printer specifically for go/format and cmd/gofmt.
	printerNormalizeNumbers = 1 << 30
	)

	// fdSem guards the number of concurrently-open file descriptors.
	//
	// For now, this is arbitrarily set to 200, based on the observation that many
	// platforms default to a kernel limit of 256. Ideally, perhaps we should derive
	// it from rlimit on platforms that support that system call.
	//
	// File descriptors opened from outside of this package are not tracked,
	// so this limit may be approximate.
	var fdSem = make(chan bool, 200)

	var (
	rewrite func(token.FileSet, ast.File) *ast.File
	parserMode parser.Mode
	)

	func usage() {
	fmt.Fprintf(os.Stderr, "usage: gofmt [flags] [path ...]\n")
	flag.PrintDefaults()
	}

	func initParserMode() {
	parserMode = parser.ParseComments
	if *allErrors {
	parserMode \|= parser.AllErrors
	}
	// It's only -r that makes use of go/ast's object resolution,
	// so avoid the unnecessary work if the flag isn't used.
	if *rewriteRule == "" {
	parserMode \|= parser.SkipObjectResolution
	}
	}

	func isGoFile(f fs.DirEntry) bool {
	// ignore non-Go files
	name := f.Name()
	return !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".go") && !f.IsDir()
	}

	// A sequencer performs concurrent tasks that may write output, but emits that
	// output in a deterministic order.
	type sequencer struct {
	maxWeight int64
	sem *semaphore.Weighted // weighted by input bytes (an approximate proxy for memory overhead)
	prev <-chan *reporterState // 1-buffered
	}

	// newSequencer returns a sequencer that allows concurrent tasks up to maxWeight
	// and writes tasks' output to out and err.
	func newSequencer(maxWeight int64, out, err io.Writer) *sequencer {
	sem := semaphore.NewWeighted(maxWeight)
	prev := make(chan *reporterState, 1)
	prev <- &reporterState{out: out, err: err}
	return &sequencer{
	maxWeight: maxWeight,
	sem: sem,
	prev: prev,
	}
	}

	// exclusive is a weight that can be passed to a sequencer to cause
	// a task to be executed without any other concurrent tasks.
	const exclusive = -1

	// Add blocks until the sequencer has enough weight to spare, then adds f as a
	// task to be executed concurrently.
	//
	// If the weight is either negative or larger than the sequencer's maximum
	// weight, Add blocks until all other tasks have completed, then the task
	// executes exclusively (blocking all other calls to Add until it completes).
	//
	// f may run concurrently in a goroutine, but its output to the passed-in
	// reporter will be sequential relative to the other tasks in the sequencer.
	//
	// If f invokes a method on the reporter, execution of that method may block
	// until the previous task has finished. (To maximize concurrency, f should
	// avoid invoking the reporter until it has finished any parallelizable work.)
	//
	// If f returns a non-nil error, that error will be reported after f's output
	// (if any) and will cause a nonzero final exit code.
	func (s sequencer) Add(weight int64, f func(reporter) error) {
	if weight < 0 \|\| weight > s.maxWeight {
	weight = s.maxWeight
	}
	if err := s.sem.Acquire(context.TODO(), weight); err != nil {
	// Change the task from "execute f" to "report err".
	weight = 0
	f = func(*reporter) error { return err }
	}

	r := &reporter{prev: s.prev}
	next := make(chan *reporterState, 1)
	s.prev = next

	// Start f in parallel: it can run until it invokes a method on r, at which
	// point it will block until the previous task releases the output state.
	go func() {
	if err := f(r); err != nil {
	r.Report(err)
	}
	next <- r.getState() // Release the next task.
	s.sem.Release(weight)
	}()
	}

	// AddReport prints an error to s after the output of any previously-added
	// tasks, causing the final exit code to be nonzero.
	func (s *sequencer) AddReport(err error) {
	s.Add(0, func(*reporter) error { return err })
	}

	// GetExitCode waits for all previously-added tasks to complete, then returns an
	// exit code for the sequence suitable for passing to os.Exit.
	func (s *sequencer) GetExitCode() int {
	c := make(chan int, 1)
	s.Add(0, func(r *reporter) error {
	c <- r.ExitCode()
	return nil
	})
	return <-c
	}

	// A reporter reports output, warnings, and errors.
	type reporter struct {
	prev <-chan *reporterState
	state *reporterState
	}

	// reporterState carries the state of a reporter instance.
	//
	// Only one reporter at a time may have access to a reporterState.
	type reporterState struct {
	out, err io.Writer
	exitCode int
	}

	// getState blocks until any prior reporters are finished with the reporter
	// state, then returns the state for manipulation.
	func (r reporter) getState() reporterState {
	if r.state == nil {
	r.state = <-r.prev
	}
	return r.state
	}

	// Warnf emits a warning message to the reporter's error stream,
	// without changing its exit code.
	func (r *reporter) Warnf(format string, args ...any) {
	fmt.Fprintf(r.getState().err, format, args...)
	}

	// Write emits a slice to the reporter's output stream.
	//
	// Any error is returned to the caller, and does not otherwise affect the
	// reporter's exit code.
	func (r *reporter) Write(p []byte) (int, error) {
	return r.getState().out.Write(p)
	}

	// Report emits a non-nil error to the reporter's error stream,
	// changing its exit code to a nonzero value.
	func (r *reporter) Report(err error) {
	if err == nil {
	panic("Report with nil error")
	}
	st := r.getState()
	scanner.PrintError(st.err, err)
	st.exitCode = 2
	}

	func (r *reporter) ExitCode() int {
	return r.getState().exitCode
	}

	// If info == nil, we are formatting stdin instead of a file.
	// If in == nil, the source is the contents of the file with the given filename.
	func processFile(filename string, info fs.FileInfo, in io.Reader, r *reporter) error {
	src, err := readFile(filename, info, in)
	if err != nil {
	return err
	}

	fileSet := token.NewFileSet()
	fragmentOk := false
	if info == nil {
	// If we are formatting stdin, we accept a program fragment in lieu of a
	// complete source file.
	fragmentOk = true
	}
	file, sourceAdj, indentAdj, err := parse(fileSet, filename, src, fragmentOk)
	if err != nil {
	return err
	}

	if rewrite != nil {
	if sourceAdj == nil {
	file = rewrite(fileSet, file)
	} else {
	r.Warnf("warning: rewrite ignored for incomplete programs\n")
	}
	}

	ast.SortImports(fileSet, file)

	if *simplifyAST {
	simplify(file)
	}

	res, err := format(fileSet, file, sourceAdj, indentAdj, src, printer.Config{Mode: printerMode, Tabwidth: tabWidth})
	if err != nil {
	return err
	}

	if !bytes.Equal(src, res) {
	// formatting has changed
	if *list {
	fmt.Fprintln(r, filename)
	}
	if *write {
	if info == nil {
	panic("-w should not have been allowed with stdin")
	}
	// make a temporary backup before overwriting original
	perm := info.Mode().Perm()
	bakname, err := backupFile(filename+".", src, perm)
	if err != nil {
	return err
	}
	fdSem <- true
	err = os.WriteFile(filename, res, perm)
	<-fdSem
	if err != nil {
	os.Rename(bakname, filename)
	return err
	}
	err = os.Remove(bakname)
	if err != nil {
	return err
	}
	}
	if *doDiff {
	newName := filepath.ToSlash(filename)
	oldName := newName + ".orig"
	r.Write(diff.Diff(oldName, src, newName, res))
	}
	}

	if !list && !write && !*doDiff {
	_, err = r.Write(res)
	}

	return err
	}

	// readFile reads the contents of filename, described by info.
	// If in is non-nil, readFile reads directly from it.
	// Otherwise, readFile opens and reads the file itself,
	// with the number of concurrently-open files limited by fdSem.
	func readFile(filename string, info fs.FileInfo, in io.Reader) ([]byte, error) {
	if in == nil {
	fdSem <- true
	var err error
	f, err := os.Open(filename)
	if err != nil {
	return nil, err
	}
	in = f
	defer func() {
	f.Close()
	<-fdSem
	}()
	}

	// Compute the file's size and read its contents with minimal allocations.
	//
	// If we have the FileInfo from filepath.WalkDir, use it to make
	// a buffer of the right size and avoid ReadAll's reallocations.
	//
	// If the size is unknown (or bogus, or overflows an int), fall back to
	// a size-independent ReadAll.
	size := -1
	if info != nil && info.Mode().IsRegular() && int64(int(info.Size())) == info.Size() {
	size = int(info.Size())
	}
	if size+1 <= 0 {
	// The file is not known to be regular, so we don't have a reliable size for it.
	var err error
	src, err := io.ReadAll(in)
	if err != nil {
	return nil, err
	}
	return src, nil
	}

	// We try to read size+1 bytes so that we can detect modifications: if we
	// read more than size bytes, then the file was modified concurrently.
	// (If that happens, we could, say, append to src to finish the read, or
	// proceed with a truncated buffer — but the fact that it changed at all
	// indicates a possible race with someone editing the file, so we prefer to
	// stop to avoid corrupting it.)
	src := make([]byte, size+1)
	n, err := io.ReadFull(in, src)
	switch err {
	case nil, io.EOF, io.ErrUnexpectedEOF:
	// io.ReadFull returns io.EOF (for an empty file) or io.ErrUnexpectedEOF
	// (for a non-empty file) if the file was changed unexpectedly. Continue
	// with comparing file sizes in those cases.
	default:
	return nil, err
	}
	if n < size {
	return nil, fmt.Errorf("error: size of %s changed during reading (from %d to %d bytes)", filename, size, n)
	} else if n > size {
	return nil, fmt.Errorf("error: size of %s changed during reading (from %d to >=%d bytes)", filename, size, len(src))
	}
	return src[:n], nil
	}

	func main() {
	// Arbitrarily limit in-flight work to 2MiB times the number of threads.
	//
	// The actual overhead for the parse tree and output will depend on the
	// specifics of the file, but this at least keeps the footprint of the process
	// roughly proportional to GOMAXPROCS.
	maxWeight := (2 << 20) * int64(runtime.GOMAXPROCS(0))
	s := newSequencer(maxWeight, os.Stdout, os.Stderr)

	// call gofmtMain in a separate function
	// so that it can use defer and have them
	// run before the exit.
	gofmtMain(s)
	os.Exit(s.GetExitCode())
	}

	func gofmtMain(s *sequencer) {
	flag.Usage = usage
	flag.Parse()

	if *cpuprofile != "" {
	fdSem <- true
	f, err := os.Create(*cpuprofile)
	if err != nil {
	s.AddReport(fmt.Errorf("creating cpu profile: %s", err))
	return
	}
	defer func() {
	f.Close()
	<-fdSem
	}()
	pprof.StartCPUProfile(f)
	defer pprof.StopCPUProfile()
	}

	initParserMode()
	initRewrite()

	args := flag.Args()
	if len(args) == 0 {
	if *write {
	s.AddReport(fmt.Errorf("error: cannot use -w with standard input"))
	return
	}
	s.Add(0, func(r *reporter) error {
	return processFile("<standard input>", nil, os.Stdin, r)
	})
	return
	}

	for _, arg := range args {
	switch info, err := os.Stat(arg); {
	case err != nil:
	s.AddReport(err)
	case !info.IsDir():
	// Non-directory arguments are always formatted.
	arg := arg
	s.Add(fileWeight(arg, info), func(r *reporter) error {
	return processFile(arg, info, nil, r)
	})
	default:
	// Directories are walked, ignoring non-Go files.
	err := filepath.WalkDir(arg, func(path string, f fs.DirEntry, err error) error {
	if err != nil \|\| !isGoFile(f) {
	return err
	}
	info, err := f.Info()
	if err != nil {
	s.AddReport(err)
	return nil
	}
	s.Add(fileWeight(path, info), func(r *reporter) error {
	return processFile(path, info, nil, r)
	})
	return nil
	})
	if err != nil {
	s.AddReport(err)
	}
	}
	}
	}

	func fileWeight(path string, info fs.FileInfo) int64 {
	if info == nil {
	return exclusive
	}
	if info.Mode().Type() == fs.ModeSymlink {
	var err error
	info, err = os.Stat(path)
	if err != nil {
	return exclusive
	}
	}
	if !info.Mode().IsRegular() {
	// For non-regular files, FileInfo.Size is system-dependent and thus not a
	// reliable indicator of weight.
	return exclusive
	}
	return info.Size()
	}

	const chmodSupported = runtime.GOOS != "windows"

	// backupFile writes data to a new file named filename<number> with permissions perm,
	// with <number randomly chosen such that the file name is unique. backupFile returns
	// the chosen file name.
	func backupFile(filename string, data []byte, perm fs.FileMode) (string, error) {
	fdSem <- true
	defer func() { <-fdSem }()

	// create backup file
	f, err := os.CreateTemp(filepath.Dir(filename), filepath.Base(filename))
	if err != nil {
	return "", err
	}
	bakname := f.Name()
	if chmodSupported {
	err = f.Chmod(perm)
	if err != nil {
	f.Close()
	os.Remove(bakname)
	return bakname, err
	}
	}

	// write data to backup file
	_, err = f.Write(data)
	if err1 := f.Close(); err == nil {
	err = err1
	}

	return bakname, err
	}