cmd/gofmt: fix race in long test

Fixes #3249.

R=rsc
CC=golang-dev
https://golang.org/cl/5792043

src/cmd/gofmt/gofmt.go

@@ -41,7 +41,7 @@ var (
 )
 
 var (
-	fset        = token.NewFileSet()
+	fileSet     = token.NewFileSet() // per process FileSet
 	exitCode    = 0
 	rewrite     func(*ast.File) *ast.File
 	parserMode  parser.Mode
@@ -98,7 +98,7 @@ func processFile(filename string, in io.Reader, out io.Writer, stdin bool) error
 		return err
 	}
 
-	file, adjust, err := parse(filename, src, stdin)
+	file, adjust, err := parse(fileSet, filename, src, stdin)
 	if err != nil {
 		return err
 	}
@@ -111,14 +111,14 @@ func processFile(filename string, in io.Reader, out io.Writer, stdin bool) error
 		}
 	}
 
-	ast.SortImports(fset, file)
+	ast.SortImports(fileSet, file)
 
 	if *simplifyAST {
 		simplify(file)
 	}
 
 	var buf bytes.Buffer
-	err = (&printer.Config{Mode: printerMode, Tabwidth: *tabWidth}).Fprint(&buf, fset, file)
+	err = (&printer.Config{Mode: printerMode, Tabwidth: *tabWidth}).Fprint(&buf, fileSet, file)
 	if err != nil {
 		return err
 	}
@@ -254,7 +254,7 @@ func diff(b1, b2 []byte) (data []byte, err error) {
 
 // parse parses src, which was read from filename,
 // as a Go source file or statement list.
-func parse(filename string, src []byte, stdin bool) (*ast.File, func(orig, src []byte) []byte, error) {
+func parse(fset *token.FileSet, filename string, src []byte, stdin bool) (*ast.File, func(orig, src []byte) []byte, error) {
 	// Try as whole source file.
 	file, err := parser.ParseFile(fset, filename, src, parserMode)
 	if err == nil {

src/cmd/gofmt/long_test.go

@@ -14,6 +14,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/printer"
+	"go/token"
 	"io"
 	"os"
 	"path/filepath"
@@ -30,8 +31,8 @@ var (
 	nfiles  int // number of files processed
 )
 
-func gofmt(filename string, src *bytes.Buffer) error {
-	f, _, err := parse(filename, src.Bytes(), false)
+func gofmt(fset *token.FileSet, filename string, src *bytes.Buffer) error {
+	f, _, err := parse(fset, filename, src.Bytes(), false)
 	if err != nil {
 		return err
 	}
@@ -58,7 +59,8 @@ func testFile(t *testing.T, b1, b2 *bytes.Buffer, filename string) {
 	}
 
 	// exclude files w/ syntax errors (typically test cases)
-	if _, _, err = parse(filename, b1.Bytes(), false); err != nil {
+	fset := token.NewFileSet()
+	if _, _, err = parse(fset, filename, b1.Bytes(), false); err != nil {
 		if *verbose {
 			fmt.Fprintf(os.Stderr, "ignoring %s\n", err)
 		}
@@ -66,7 +68,7 @@ func testFile(t *testing.T, b1, b2 *bytes.Buffer, filename string) {
 	}
 
 	// gofmt file
-	if err = gofmt(filename, b1); err != nil {
+	if err = gofmt(fset, filename, b1); err != nil {
 		t.Errorf("1st gofmt failed: %v", err)
 		return
 	}
@@ -76,7 +78,7 @@ func testFile(t *testing.T, b1, b2 *bytes.Buffer, filename string) {
 	b2.Write(b1.Bytes())
 
 	// gofmt result again
-	if err = gofmt(filename, b2); err != nil {
+	if err = gofmt(fset, filename, b2); err != nil {
 		t.Errorf("2nd gofmt failed: %v", err)
 		return
 	}