gofmt: minor refactor to permit easy testing

R=rsc
CC=golang-dev
https://golang.org/cl/4397046

src/cmd/gofmt/gofmt.go

@@ -13,6 +13,7 @@ import (
 	"go/printer"
 	"go/scanner"
 	"go/token"
+	"io"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -86,14 +87,23 @@ func isGoFile(f *os.FileInfo) bool {
 }
 
 
-func processFile(f *os.File) os.Error {
-	src, err := ioutil.ReadAll(f)
+// 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) os.Error {
+	if in == nil {
+		f, err := os.Open(filename)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+		in = f
+	}
+
+	src, err := ioutil.ReadAll(in)
 	if err != nil {
 		return err
 	}
 
-	file, err := parser.ParseFile(fset, f.Name(), src, parserMode)
-
+	file, err := parser.ParseFile(fset, filename, src, parserMode)
 	if err != nil {
 		return err
 	}
@@ -116,10 +126,10 @@ func processFile(f *os.File) os.Error {
 	if !bytes.Equal(src, res) {
 		// formatting has changed
 		if *list {
-			fmt.Fprintln(os.Stdout, f.Name())
+			fmt.Fprintln(out, filename)
 		}
 		if *write {
-			err = ioutil.WriteFile(f.Name(), res, 0)
+			err = ioutil.WriteFile(filename, res, 0)
 			if err != nil {
 				return err
 			}
@@ -127,23 +137,13 @@ func processFile(f *os.File) os.Error {
 	}
 
 	if !*list && !*write {
-		_, err = os.Stdout.Write(res)
+		_, err = out.Write(res)
 	}
 
 	return err
 }
 
 
-func processFileByName(filename string) os.Error {
-	file, err := os.Open(filename)
-	if err != nil {
-		return err
-	}
-	defer file.Close()
-	return processFile(file)
-}
-
-
 type fileVisitor chan os.Error
 
 func (v fileVisitor) VisitDir(path string, f *os.FileInfo) bool {
@@ -154,7 +154,7 @@ func (v fileVisitor) VisitDir(path string, f *os.FileInfo) bool {
 func (v fileVisitor) VisitFile(path string, f *os.FileInfo) {
 	if isGoFile(f) {
 		v <- nil // synchronize error handler
-		if err := processFileByName(path); err != nil {
+		if err := processFile(path, nil, os.Stdout); err != nil {
 			v <- err
 		}
 	}
@@ -210,9 +210,10 @@ func gofmtMain() {
 	initRewrite()
 
 	if flag.NArg() == 0 {
-		if err := processFile(os.Stdin); err != nil {
+		if err := processFile("<standard input>", os.Stdin, os.Stdout); err != nil {
 			report(err)
 		}
+		return
 	}
 
 	for i := 0; i < flag.NArg(); i++ {
@@ -221,7 +222,7 @@ func gofmtMain() {
 		case err != nil:
 			report(err)
 		case dir.IsRegular():
-			if err := processFileByName(path); err != nil {
+			if err := processFile(path, nil, os.Stdout); err != nil {
 				report(err)
 			}
 		case dir.IsDirectory():