src/cmd/gofmt/gofmt.go

// 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)
			if err != nil {
				return fmt.Errorf("computing diff: %s", err)
			}
			fmt.Printf("diff %s gofmt/%s\n", filename, 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 diff(b1, b2 []byte) (data []byte, err error) {
	f1, err := ioutil.TempFile("", "gofmt")
	if err != nil {
		return
	}
	defer os.Remove(f1.Name())
	defer f1.Close()

	f2, err := ioutil.TempFile("", "gofmt")
	if err != nil {
		return
	}
	defer os.Remove(f2.Name())
	defer f2.Close()

	f1.Write(b1)
	f2.Write(b2)

	data, err = exec.Command("diff", "-u", f1.Name(), f2.Name()).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.
		err = nil
	}
	return

}

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
}