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, 8 insertions, 42 deletions

diff --git a/src/cmd/gofmt/gofmt.go b/src/cmd/gofmt/gofmt.go
index d7a77a9682..9e472b2d51 100644
--- a/src/cmd/gofmt/gofmt.go
+++ b/src/cmd/gofmt/gofmt.go
@@ -16,11 +16,12 @@ import (
 	"io"
 	"io/ioutil"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"runtime"
 	"runtime/pprof"
 	"strings"
+
+	"cmd/internal/diff"
 )
 
 var (
@@ -141,7 +142,7 @@ func processFile(filename string, in io.Reader, out io.Writer, stdin bool) error
 			}
 		}
 		if *doDiff {
-			data, err := diff(src, res, filename)
+			data, err := diffWithReplaceTempFile(src, res, filename)
 			if err != nil {
 				return fmt.Errorf("computing diff: %s", err)
 			}
@@ -227,47 +228,12 @@ func gofmtMain() {
 	}
 }
 
-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()
+func diffWithReplaceTempFile(b1, b2 []byte, filename string) ([]byte, error) {
+	data, err := diff.Diff("gofmt", b1, b2)
 	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
+	return data, err
 }
 
 // replaceTempFilename replaces temporary filenames in diff with actual one.
diff --git a/src/cmd/gofmt/gofmt_test.go b/src/cmd/gofmt/gofmt_test.go
index 3008365cd2..98d3eb7eb2 100644
--- a/src/cmd/gofmt/gofmt_test.go
+++ b/src/cmd/gofmt/gofmt_test.go
@@ -112,7 +112,7 @@ func runTest(t *testing.T, in, out string) {
 		}
 
 		t.Errorf("(gofmt %s) != %s (see %s.gofmt)", in, out, in)
-		d, err := diff(expected, got, in)
+		d, err := diffWithReplaceTempFile(expected, got, in)
 		if err == nil {
 			t.Errorf("%s", d)
 		}
@@ -194,7 +194,7 @@ func TestDiff(t *testing.T) {
 	in := []byte("first\nsecond\n")
 	out := []byte("first\nthird\n")
 	filename := "difftest.txt"
-	b, err := diff(in, out, filename)
+	b, err := diffWithReplaceTempFile(in, out, filename)
 	if err != nil {
 		t.Fatal(err)
 	}