gofmt.go

Documentation: cmd/gofmt

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package main
     6  
     7  import (
     8  	"bytes"
     9  	"context"
    10  	"flag"
    11  	"fmt"
    12  	"go/ast"
    13  	"go/parser"
    14  	"go/printer"
    15  	"go/scanner"
    16  	"go/token"
    17  	"internal/diff"
    18  	"io"
    19  	"io/fs"
    20  	"math/rand"
    21  	"os"
    22  	"path/filepath"
    23  	"runtime"
    24  	"runtime/pprof"
    25  	"strconv"
    26  	"strings"
    27  
    28  	"cmd/internal/telemetry/counter"
    29  
    30  	"golang.org/x/sync/semaphore"
    31  )
    32  
    33  var (
    34  	// main operation modes
    35  	list        = flag.Bool("l", false, "list files whose formatting differs from gofmt's")
    36  	write       = flag.Bool("w", false, "write result to (source) file instead of stdout")
    37  	rewriteRule = flag.String("r", "", "rewrite rule (e.g., 'a[b:len(a)] -> a[b:]')")
    38  	simplifyAST = flag.Bool("s", false, "simplify code")
    39  	doDiff      = flag.Bool("d", false, "display diffs instead of rewriting files")
    40  	allErrors   = flag.Bool("e", false, "report all errors (not just the first 10 on different lines)")
    41  
    42  	// debugging
    43  	cpuprofile = flag.String("cpuprofile", "", "write cpu profile to this file")
    44  )
    45  
    46  // Keep these in sync with go/format/format.go.
    47  const (
    48  	tabWidth    = 8
    49  	printerMode = printer.UseSpaces | printer.TabIndent | printerNormalizeNumbers
    50  
    51  	// printerNormalizeNumbers means to canonicalize number literal prefixes
    52  	// and exponents while printing. See https://golang.org/doc/go1.13#gofmt.
    53  	//
    54  	// This value is defined in go/printer specifically for go/format and cmd/gofmt.
    55  	printerNormalizeNumbers = 1 << 30
    56  )
    57  
    58  // fdSem guards the number of concurrently-open file descriptors.
    59  //
    60  // For now, this is arbitrarily set to 200, based on the observation that many
    61  // platforms default to a kernel limit of 256. Ideally, perhaps we should derive
    62  // it from rlimit on platforms that support that system call.
    63  //
    64  // File descriptors opened from outside of this package are not tracked,
    65  // so this limit may be approximate.
    66  var fdSem = make(chan bool, 200)
    67  
    68  var (
    69  	rewrite    func(*token.FileSet, *ast.File) *ast.File
    70  	parserMode parser.Mode
    71  )
    72  
    73  func usage() {
    74  	fmt.Fprintf(os.Stderr, "usage: gofmt [flags] [path ...]\n")
    75  	flag.PrintDefaults()
    76  }
    77  
    78  func initParserMode() {
    79  	parserMode = parser.ParseComments
    80  	if *allErrors {
    81  		parserMode |= parser.AllErrors
    82  	}
    83  	// It's only -r that makes use of go/ast's object resolution,
    84  	// so avoid the unnecessary work if the flag isn't used.
    85  	if *rewriteRule == "" {
    86  		parserMode |= parser.SkipObjectResolution
    87  	}
    88  }
    89  
    90  func isGoFile(f fs.DirEntry) bool {
    91  	// ignore non-Go files
    92  	name := f.Name()
    93  	return !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".go") && !f.IsDir()
    94  }
    95  
    96  // A sequencer performs concurrent tasks that may write output, but emits that
    97  // output in a deterministic order.
    98  type sequencer struct {
    99  	maxWeight int64
   100  	sem       *semaphore.Weighted   // weighted by input bytes (an approximate proxy for memory overhead)
   101  	prev      <-chan *reporterState // 1-buffered
   102  }
   103  
   104  // newSequencer returns a sequencer that allows concurrent tasks up to maxWeight
   105  // and writes tasks' output to out and err.
   106  func newSequencer(maxWeight int64, out, err io.Writer) *sequencer {
   107  	sem := semaphore.NewWeighted(maxWeight)
   108  	prev := make(chan *reporterState, 1)
   109  	prev <- &reporterState{out: out, err: err}
   110  	return &sequencer{
   111  		maxWeight: maxWeight,
   112  		sem:       sem,
   113  		prev:      prev,
   114  	}
   115  }
   116  
   117  // exclusive is a weight that can be passed to a sequencer to cause
   118  // a task to be executed without any other concurrent tasks.
   119  const exclusive = -1
   120  
   121  // Add blocks until the sequencer has enough weight to spare, then adds f as a
   122  // task to be executed concurrently.
   123  //
   124  // If the weight is either negative or larger than the sequencer's maximum
   125  // weight, Add blocks until all other tasks have completed, then the task
   126  // executes exclusively (blocking all other calls to Add until it completes).
   127  //
   128  // f may run concurrently in a goroutine, but its output to the passed-in
   129  // reporter will be sequential relative to the other tasks in the sequencer.
   130  //
   131  // If f invokes a method on the reporter, execution of that method may block
   132  // until the previous task has finished. (To maximize concurrency, f should
   133  // avoid invoking the reporter until it has finished any parallelizable work.)
   134  //
   135  // If f returns a non-nil error, that error will be reported after f's output
   136  // (if any) and will cause a nonzero final exit code.
   137  func (s *sequencer) Add(weight int64, f func(*reporter) error) {
   138  	if weight < 0 || weight > s.maxWeight {
   139  		weight = s.maxWeight
   140  	}
   141  	if err := s.sem.Acquire(context.TODO(), weight); err != nil {
   142  		// Change the task from "execute f" to "report err".
   143  		weight = 0
   144  		f = func(*reporter) error { return err }
   145  	}
   146  
   147  	r := &reporter{prev: s.prev}
   148  	next := make(chan *reporterState, 1)
   149  	s.prev = next
   150  
   151  	// Start f in parallel: it can run until it invokes a method on r, at which
   152  	// point it will block until the previous task releases the output state.
   153  	go func() {
   154  		if err := f(r); err != nil {
   155  			r.Report(err)
   156  		}
   157  		next <- r.getState() // Release the next task.
   158  		s.sem.Release(weight)
   159  	}()
   160  }
   161  
   162  // AddReport prints an error to s after the output of any previously-added
   163  // tasks, causing the final exit code to be nonzero.
   164  func (s *sequencer) AddReport(err error) {
   165  	s.Add(0, func(*reporter) error { return err })
   166  }
   167  
   168  // GetExitCode waits for all previously-added tasks to complete, then returns an
   169  // exit code for the sequence suitable for passing to os.Exit.
   170  func (s *sequencer) GetExitCode() int {
   171  	c := make(chan int, 1)
   172  	s.Add(0, func(r *reporter) error {
   173  		c <- r.ExitCode()
   174  		return nil
   175  	})
   176  	return <-c
   177  }
   178  
   179  // A reporter reports output, warnings, and errors.
   180  type reporter struct {
   181  	prev  <-chan *reporterState
   182  	state *reporterState
   183  }
   184  
   185  // reporterState carries the state of a reporter instance.
   186  //
   187  // Only one reporter at a time may have access to a reporterState.
   188  type reporterState struct {
   189  	out, err io.Writer
   190  	exitCode int
   191  }
   192  
   193  // getState blocks until any prior reporters are finished with the reporter
   194  // state, then returns the state for manipulation.
   195  func (r *reporter) getState() *reporterState {
   196  	if r.state == nil {
   197  		r.state = <-r.prev
   198  	}
   199  	return r.state
   200  }
   201  
   202  // Warnf emits a warning message to the reporter's error stream,
   203  // without changing its exit code.
   204  func (r *reporter) Warnf(format string, args ...any) {
   205  	fmt.Fprintf(r.getState().err, format, args...)
   206  }
   207  
   208  // Write emits a slice to the reporter's output stream.
   209  //
   210  // Any error is returned to the caller, and does not otherwise affect the
   211  // reporter's exit code.
   212  func (r *reporter) Write(p []byte) (int, error) {
   213  	return r.getState().out.Write(p)
   214  }
   215  
   216  // Report emits a non-nil error to the reporter's error stream,
   217  // changing its exit code to a nonzero value.
   218  func (r *reporter) Report(err error) {
   219  	if err == nil {
   220  		panic("Report with nil error")
   221  	}
   222  	st := r.getState()
   223  	scanner.PrintError(st.err, err)
   224  	st.exitCode = 2
   225  }
   226  
   227  func (r *reporter) ExitCode() int {
   228  	return r.getState().exitCode
   229  }
   230  
   231  // If info == nil, we are formatting stdin instead of a file.
   232  // If in == nil, the source is the contents of the file with the given filename.
   233  func processFile(filename string, info fs.FileInfo, in io.Reader, r *reporter) error {
   234  	src, err := readFile(filename, info, in)
   235  	if err != nil {
   236  		return err
   237  	}
   238  
   239  	fileSet := token.NewFileSet()
   240  	// If we are formatting stdin, we accept a program fragment in lieu of a
   241  	// complete source file.
   242  	fragmentOk := info == nil
   243  	file, sourceAdj, indentAdj, err := parse(fileSet, filename, src, fragmentOk)
   244  	if err != nil {
   245  		return err
   246  	}
   247  
   248  	if rewrite != nil {
   249  		if sourceAdj == nil {
   250  			file = rewrite(fileSet, file)
   251  		} else {
   252  			r.Warnf("warning: rewrite ignored for incomplete programs\n")
   253  		}
   254  	}
   255  
   256  	ast.SortImports(fileSet, file)
   257  
   258  	if *simplifyAST {
   259  		simplify(file)
   260  	}
   261  
   262  	res, err := format(fileSet, file, sourceAdj, indentAdj, src, printer.Config{Mode: printerMode, Tabwidth: tabWidth})
   263  	if err != nil {
   264  		return err
   265  	}
   266  
   267  	if !bytes.Equal(src, res) {
   268  		// formatting has changed
   269  		if *list {
   270  			fmt.Fprintln(r, filename)
   271  		}
   272  		if *write {
   273  			if info == nil {
   274  				panic("-w should not have been allowed with stdin")
   275  			}
   276  
   277  			perm := info.Mode().Perm()
   278  			if err := writeFile(filename, src, res, perm, info.Size()); err != nil {
   279  				return err
   280  			}
   281  		}
   282  		if *doDiff {
   283  			newName := filepath.ToSlash(filename)
   284  			oldName := newName + ".orig"
   285  			r.Write(diff.Diff(oldName, src, newName, res))
   286  		}
   287  	}
   288  
   289  	if !*list && !*write && !*doDiff {
   290  		_, err = r.Write(res)
   291  	}
   292  
   293  	return err
   294  }
   295  
   296  // readFile reads the contents of filename, described by info.
   297  // If in is non-nil, readFile reads directly from it.
   298  // Otherwise, readFile opens and reads the file itself,
   299  // with the number of concurrently-open files limited by fdSem.
   300  func readFile(filename string, info fs.FileInfo, in io.Reader) ([]byte, error) {
   301  	if in == nil {
   302  		fdSem <- true
   303  		var err error
   304  		f, err := os.Open(filename)
   305  		if err != nil {
   306  			return nil, err
   307  		}
   308  		in = f
   309  		defer func() {
   310  			f.Close()
   311  			<-fdSem
   312  		}()
   313  	}
   314  
   315  	// Compute the file's size and read its contents with minimal allocations.
   316  	//
   317  	// If we have the FileInfo from filepath.WalkDir, use it to make
   318  	// a buffer of the right size and avoid ReadAll's reallocations.
   319  	//
   320  	// If the size is unknown (or bogus, or overflows an int), fall back to
   321  	// a size-independent ReadAll.
   322  	size := -1
   323  	if info != nil && info.Mode().IsRegular() && int64(int(info.Size())) == info.Size() {
   324  		size = int(info.Size())
   325  	}
   326  	if size+1 <= 0 {
   327  		// The file is not known to be regular, so we don't have a reliable size for it.
   328  		var err error
   329  		src, err := io.ReadAll(in)
   330  		if err != nil {
   331  			return nil, err
   332  		}
   333  		return src, nil
   334  	}
   335  
   336  	// We try to read size+1 bytes so that we can detect modifications: if we
   337  	// read more than size bytes, then the file was modified concurrently.
   338  	// (If that happens, we could, say, append to src to finish the read, or
   339  	// proceed with a truncated buffer — but the fact that it changed at all
   340  	// indicates a possible race with someone editing the file, so we prefer to
   341  	// stop to avoid corrupting it.)
   342  	src := make([]byte, size+1)
   343  	n, err := io.ReadFull(in, src)
   344  	switch err {
   345  	case nil, io.EOF, io.ErrUnexpectedEOF:
   346  		// io.ReadFull returns io.EOF (for an empty file) or io.ErrUnexpectedEOF
   347  		// (for a non-empty file) if the file was changed unexpectedly. Continue
   348  		// with comparing file sizes in those cases.
   349  	default:
   350  		return nil, err
   351  	}
   352  	if n < size {
   353  		return nil, fmt.Errorf("error: size of %s changed during reading (from %d to %d bytes)", filename, size, n)
   354  	} else if n > size {
   355  		return nil, fmt.Errorf("error: size of %s changed during reading (from %d to >=%d bytes)", filename, size, len(src))
   356  	}
   357  	return src[:n], nil
   358  }
   359  
   360  func main() {
   361  	// Arbitrarily limit in-flight work to 2MiB times the number of threads.
   362  	//
   363  	// The actual overhead for the parse tree and output will depend on the
   364  	// specifics of the file, but this at least keeps the footprint of the process
   365  	// roughly proportional to GOMAXPROCS.
   366  	maxWeight := (2 << 20) * int64(runtime.GOMAXPROCS(0))
   367  	s := newSequencer(maxWeight, os.Stdout, os.Stderr)
   368  
   369  	// call gofmtMain in a separate function
   370  	// so that it can use defer and have them
   371  	// run before the exit.
   372  	gofmtMain(s)
   373  	os.Exit(s.GetExitCode())
   374  }
   375  
   376  func gofmtMain(s *sequencer) {
   377  	counter.Open()
   378  	flag.Usage = usage
   379  	flag.Parse()
   380  	counter.Inc("gofmt/invocations")
   381  	counter.CountFlags("gofmt/flag:", *flag.CommandLine)
   382  
   383  	if *cpuprofile != "" {
   384  		fdSem <- true
   385  		f, err := os.Create(*cpuprofile)
   386  		if err != nil {
   387  			s.AddReport(fmt.Errorf("creating cpu profile: %s", err))
   388  			return
   389  		}
   390  		defer func() {
   391  			f.Close()
   392  			<-fdSem
   393  		}()
   394  		pprof.StartCPUProfile(f)
   395  		defer pprof.StopCPUProfile()
   396  	}
   397  
   398  	initParserMode()
   399  	initRewrite()
   400  
   401  	args := flag.Args()
   402  	if len(args) == 0 {
   403  		if *write {
   404  			s.AddReport(fmt.Errorf("error: cannot use -w with standard input"))
   405  			return
   406  		}
   407  		s.Add(0, func(r *reporter) error {
   408  			return processFile("<standard input>", nil, os.Stdin, r)
   409  		})
   410  		return
   411  	}
   412  
   413  	for _, arg := range args {
   414  		switch info, err := os.Stat(arg); {
   415  		case err != nil:
   416  			s.AddReport(err)
   417  		case !info.IsDir():
   418  			// Non-directory arguments are always formatted.
   419  			arg := arg
   420  			s.Add(fileWeight(arg, info), func(r *reporter) error {
   421  				return processFile(arg, info, nil, r)
   422  			})
   423  		default:
   424  			// Directories are walked, ignoring non-Go files.
   425  			err := filepath.WalkDir(arg, func(path string, f fs.DirEntry, err error) error {
   426  				if err != nil || !isGoFile(f) {
   427  					return err
   428  				}
   429  				info, err := f.Info()
   430  				if err != nil {
   431  					s.AddReport(err)
   432  					return nil
   433  				}
   434  				s.Add(fileWeight(path, info), func(r *reporter) error {
   435  					return processFile(path, info, nil, r)
   436  				})
   437  				return nil
   438  			})
   439  			if err != nil {
   440  				s.AddReport(err)
   441  			}
   442  		}
   443  	}
   444  }
   445  
   446  func fileWeight(path string, info fs.FileInfo) int64 {
   447  	if info == nil {
   448  		return exclusive
   449  	}
   450  	if info.Mode().Type() == fs.ModeSymlink {
   451  		var err error
   452  		info, err = os.Stat(path)
   453  		if err != nil {
   454  			return exclusive
   455  		}
   456  	}
   457  	if !info.Mode().IsRegular() {
   458  		// For non-regular files, FileInfo.Size is system-dependent and thus not a
   459  		// reliable indicator of weight.
   460  		return exclusive
   461  	}
   462  	return info.Size()
   463  }
   464  
   465  // writeFile updates a file with the new formatted data.
   466  func writeFile(filename string, orig, formatted []byte, perm fs.FileMode, size int64) error {
   467  	// Make a temporary backup file before rewriting the original file.
   468  	bakname, err := backupFile(filename, orig, perm)
   469  	if err != nil {
   470  		return err
   471  	}
   472  
   473  	fdSem <- true
   474  	defer func() { <-fdSem }()
   475  
   476  	fout, err := os.OpenFile(filename, os.O_WRONLY, perm)
   477  	if err != nil {
   478  		// We couldn't even open the file, so it should
   479  		// not have changed.
   480  		os.Remove(bakname)
   481  		return err
   482  	}
   483  	defer fout.Close() // for error paths
   484  
   485  	restoreFail := func(err error) {
   486  		fmt.Fprintf(os.Stderr, "gofmt: %s: error restoring file to original: %v; backup in %s\n", filename, err, bakname)
   487  	}
   488  
   489  	n, err := fout.Write(formatted)
   490  	if err == nil && int64(n) < size {
   491  		err = fout.Truncate(int64(n))
   492  	}
   493  
   494  	if err != nil {
   495  		// Rewriting the file failed.
   496  
   497  		if n == 0 {
   498  			// Original file unchanged.
   499  			os.Remove(bakname)
   500  			return err
   501  		}
   502  
   503  		// Try to restore the original contents.
   504  
   505  		no, erro := fout.WriteAt(orig, 0)
   506  		if erro != nil {
   507  			// That failed too.
   508  			restoreFail(erro)
   509  			return err
   510  		}
   511  
   512  		if no < n {
   513  			// Original file is shorter. Truncate.
   514  			if erro = fout.Truncate(int64(no)); erro != nil {
   515  				restoreFail(erro)
   516  				return err
   517  			}
   518  		}
   519  
   520  		if erro := fout.Close(); erro != nil {
   521  			restoreFail(erro)
   522  			return err
   523  		}
   524  
   525  		// Original contents restored.
   526  		os.Remove(bakname)
   527  		return err
   528  	}
   529  
   530  	if err := fout.Close(); err != nil {
   531  		restoreFail(err)
   532  		return err
   533  	}
   534  
   535  	// File updated.
   536  	os.Remove(bakname)
   537  	return nil
   538  }
   539  
   540  // backupFile writes data to a new file named filename<number> with permissions perm,
   541  // with <number> randomly chosen such that the file name is unique. backupFile returns
   542  // the chosen file name.
   543  func backupFile(filename string, data []byte, perm fs.FileMode) (string, error) {
   544  	fdSem <- true
   545  	defer func() { <-fdSem }()
   546  
   547  	nextRandom := func() string {
   548  		return strconv.Itoa(rand.Int())
   549  	}
   550  
   551  	dir, base := filepath.Split(filename)
   552  	var (
   553  		bakname string
   554  		f       *os.File
   555  	)
   556  	for {
   557  		bakname = filepath.Join(dir, base+"."+nextRandom())
   558  		var err error
   559  		f, err = os.OpenFile(bakname, os.O_RDWR|os.O_CREATE|os.O_EXCL, perm)
   560  		if err == nil {
   561  			break
   562  		}
   563  		if !os.IsExist(err) {
   564  			return "", err
   565  		}
   566  	}
   567  
   568  	// write data to backup file
   569  	_, err := f.Write(data)
   570  	if err1 := f.Close(); err == nil {
   571  		err = err1
   572  	}
   573  
   574  	return bakname, err
   575  }
   576
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