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Source file src/cmd/gofmt/gofmt.go

Documentation: cmd/gofmt

  // 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"
  	"flag"
  	"fmt"
  	"go/ast"
  	"go/parser"
  	"go/printer"
  	"go/scanner"
  	"go/token"
  	"io"
  	"io/ioutil"
  	"os"
  	"os/exec"
  	"path/filepath"
  	"runtime"
  	"runtime/pprof"
  	"strings"
  )
  
  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")
  )
  
  const (
  	tabWidth    = 8
  	printerMode = printer.UseSpaces | printer.TabIndent
  )
  
  var (
  	fileSet    = token.NewFileSet() // per process FileSet
  	exitCode   = 0
  	rewrite    func(*ast.File) *ast.File
  	parserMode parser.Mode
  )
  
  func report(err error) {
  	scanner.PrintError(os.Stderr, err)
  	exitCode = 2
  }
  
  func usage() {
  	fmt.Fprintf(os.Stderr, "usage: gofmt [flags] [path ...]\n")
  	flag.PrintDefaults()
  }
  
  func initParserMode() {
  	parserMode = parser.ParseComments
  	if *allErrors {
  		parserMode |= parser.AllErrors
  	}
  }
  
  func isGoFile(f os.FileInfo) bool {
  	// ignore non-Go files
  	name := f.Name()
  	return !f.IsDir() && !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".go")
  }
  
  // If in == nil, the source is the contents of the file with the given filename.
  func processFile(filename string, in io.Reader, out io.Writer, stdin bool) error {
  	var perm os.FileMode = 0644
  	if in == nil {
  		f, err := os.Open(filename)
  		if err != nil {
  			return err
  		}
  		defer f.Close()
  		fi, err := f.Stat()
  		if err != nil {
  			return err
  		}
  		in = f
  		perm = fi.Mode().Perm()
  	}
  
  	src, err := ioutil.ReadAll(in)
  	if err != nil {
  		return err
  	}
  
  	file, sourceAdj, indentAdj, err := parse(fileSet, filename, src, stdin)
  	if err != nil {
  		return err
  	}
  
  	if rewrite != nil {
  		if sourceAdj == nil {
  			file = rewrite(file)
  		} else {
  			fmt.Fprintf(os.Stderr, "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(out, filename)
  		}
  		if *write {
  			// make a temporary backup before overwriting original
  			bakname, err := backupFile(filename+".", src, perm)
  			if err != nil {
  				return err
  			}
  			err = ioutil.WriteFile(filename, res, perm)
  			if err != nil {
  				os.Rename(bakname, filename)
  				return err
  			}
  			err = os.Remove(bakname)
  			if err != nil {
  				return err
  			}
  		}
  		if *doDiff {
  			data, err := diff(src, res, filename)
  			if err != nil {
  				return fmt.Errorf("computing diff: %s", err)
  			}
  			fmt.Printf("diff -u %s %s\n", filepath.ToSlash(filename+".orig"), filepath.ToSlash(filename))
  			out.Write(data)
  		}
  	}
  
  	if !*list && !*write && !*doDiff {
  		_, err = out.Write(res)
  	}
  
  	return err
  }
  
  func visitFile(path string, f os.FileInfo, err error) error {
  	if err == nil && isGoFile(f) {
  		err = processFile(path, nil, os.Stdout, false)
  	}
  	// Don't complain if a file was deleted in the meantime (i.e.
  	// the directory changed concurrently while running gofmt).
  	if err != nil && !os.IsNotExist(err) {
  		report(err)
  	}
  	return nil
  }
  
  func walkDir(path string) {
  	filepath.Walk(path, visitFile)
  }
  
  func main() {
  	// call gofmtMain in a separate function
  	// so that it can use defer and have them
  	// run before the exit.
  	gofmtMain()
  	os.Exit(exitCode)
  }
  
  func gofmtMain() {
  	flag.Usage = usage
  	flag.Parse()
  
  	if *cpuprofile != "" {
  		f, err := os.Create(*cpuprofile)
  		if err != nil {
  			fmt.Fprintf(os.Stderr, "creating cpu profile: %s\n", err)
  			exitCode = 2
  			return
  		}
  		defer f.Close()
  		pprof.StartCPUProfile(f)
  		defer pprof.StopCPUProfile()
  	}
  
  	initParserMode()
  	initRewrite()
  
  	if flag.NArg() == 0 {
  		if *write {
  			fmt.Fprintln(os.Stderr, "error: cannot use -w with standard input")
  			exitCode = 2
  			return
  		}
  		if err := processFile("<standard input>", os.Stdin, os.Stdout, true); err != nil {
  			report(err)
  		}
  		return
  	}
  
  	for i := 0; i < flag.NArg(); i++ {
  		path := flag.Arg(i)
  		switch dir, err := os.Stat(path); {
  		case err != nil:
  			report(err)
  		case dir.IsDir():
  			walkDir(path)
  		default:
  			if err := processFile(path, nil, os.Stdout, false); err != nil {
  				report(err)
  			}
  		}
  	}
  }
  
  func writeTempFile(dir, prefix string, data []byte) (string, error) {
  	file, err := ioutil.TempFile(dir, prefix)
  	if err != nil {
  		return "", err
  	}
  	_, err = file.Write(data)
  	if err1 := file.Close(); err == nil {
  		err = err1
  	}
  	if err != nil {
  		os.Remove(file.Name())
  		return "", err
  	}
  	return file.Name(), nil
  }
  
  func diff(b1, b2 []byte, filename string) (data []byte, err error) {
  	f1, err := writeTempFile("", "gofmt", b1)
  	if err != nil {
  		return
  	}
  	defer os.Remove(f1)
  
  	f2, err := writeTempFile("", "gofmt", b2)
  	if err != nil {
  		return
  	}
  	defer os.Remove(f2)
  
  	cmd := "diff"
  	if runtime.GOOS == "plan9" {
  		cmd = "/bin/ape/diff"
  	}
  
  	data, err = exec.Command(cmd, "-u", f1, f2).CombinedOutput()
  	if len(data) > 0 {
  		// diff exits with a non-zero status when the files don't match.
  		// Ignore that failure as long as we get output.
  		return replaceTempFilename(data, filename)
  	}
  	return
  }
  
  // replaceTempFilename replaces temporary filenames in diff with actual one.
  //
  // --- /tmp/gofmt316145376	2017-02-03 19:13:00.280468375 -0500
  // +++ /tmp/gofmt617882815	2017-02-03 19:13:00.280468375 -0500
  // ...
  // ->
  // --- path/to/file.go.orig	2017-02-03 19:13:00.280468375 -0500
  // +++ path/to/file.go	2017-02-03 19:13:00.280468375 -0500
  // ...
  func replaceTempFilename(diff []byte, filename string) ([]byte, error) {
  	bs := bytes.SplitN(diff, []byte{'\n'}, 3)
  	if len(bs) < 3 {
  		return nil, fmt.Errorf("got unexpected diff for %s", filename)
  	}
  	// Preserve timestamps.
  	var t0, t1 []byte
  	if i := bytes.LastIndexByte(bs[0], '\t'); i != -1 {
  		t0 = bs[0][i:]
  	}
  	if i := bytes.LastIndexByte(bs[1], '\t'); i != -1 {
  		t1 = bs[1][i:]
  	}
  	// Always print filepath with slash separator.
  	f := filepath.ToSlash(filename)
  	bs[0] = []byte(fmt.Sprintf("--- %s%s", f+".orig", t0))
  	bs[1] = []byte(fmt.Sprintf("+++ %s%s", f, t1))
  	return bytes.Join(bs, []byte{'\n'}), nil
  }
  
  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 os.FileMode) (string, error) {
  	// create backup file
  	f, err := ioutil.TempFile(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
  	n, err := f.Write(data)
  	if err == nil && n < len(data) {
  		err = io.ErrShortWrite
  	}
  	if err1 := f.Close(); err == nil {
  		err = err1
  	}
  
  	return bakname, err
  }
  

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