cmd/fix, cmd/go, cmd/gofmt: refactor common code into new internal diff package

Change-Id: Idac8473d1752059bf2f617fd7a781000ee2c3af4
GitHub-Last-Rev: 02a3aa1a3241d3ed4422518f1c954cd54bbe858e
GitHub-Pull-Request: golang/go#35141
Reviewed-on: https://go-review.googlesource.com/c/go/+/203218
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 6 insertions, 47 deletions

diff --git a/src/cmd/fix/main.go b/src/cmd/fix/main.go
index f54a5e0d96..80b3c76350 100644
--- a/src/cmd/fix/main.go
+++ b/src/cmd/fix/main.go
@@ -15,11 +15,11 @@ import (
 	"go/token"
 	"io/ioutil"
 	"os"
-	"os/exec"
 	"path/filepath"
-	"runtime"
 	"sort"
 	"strings"
+
+	"cmd/internal/diff"
 )
 
 var (
@@ -186,7 +186,7 @@ func processFile(filename string, useStdin bool) error {
 	}
 
 	if *doDiff {
-		data, err := diff(src, newSrc)
+		data, err := diff.Diff("go-fix", src, newSrc)
 		if err != nil {
 			return fmt.Errorf("computing diff: %s", err)
 		}
@@ -237,46 +237,3 @@ func isGoFile(f os.FileInfo) bool {
 	name := f.Name()
 	return !f.IsDir() && !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".go")
 }
-
-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) (data []byte, err error) {
-	f1, err := writeTempFile("", "go-fix", b1)
-	if err != nil {
-		return
-	}
-	defer os.Remove(f1)
-
-	f2, err := writeTempFile("", "go-fix", 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.
-		err = nil
-	}
-	return
-}
diff --git a/src/cmd/fix/main_test.go b/src/cmd/fix/main_test.go
index 8868140ade..ee74f24c6e 100644
--- a/src/cmd/fix/main_test.go
+++ b/src/cmd/fix/main_test.go
@@ -9,6 +9,8 @@ import (
 	"go/parser"
 	"strings"
 	"testing"
+
+	"cmd/internal/diff"
 )
 
 type testCase struct {
@@ -123,7 +125,7 @@ func TestRewrite(t *testing.T) {
 }
 
 func tdiff(t *testing.T, a, b string) {
-	data, err := diff([]byte(a), []byte(b))
+	data, err := diff.Diff("go-fix-test", []byte(a), []byte(b))
 	if err != nil {
 		t.Error(err)
 		return