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>

6 files changed, 75 insertions, 119 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
diff --git a/src/cmd/go/internal/modfile/read_test.go b/src/cmd/go/internal/modfile/read_test.go
index 32401304b9..3c88e69281 100644
--- a/src/cmd/go/internal/modfile/read_test.go
+++ b/src/cmd/go/internal/modfile/read_test.go
@@ -9,11 +9,12 @@ import (
 	"fmt"
 	"io/ioutil"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"reflect"
 	"strings"
 	"testing"
+
+	"cmd/internal/diff"
 )
 
 // exists reports whether the named file exists.
@@ -282,37 +283,9 @@ func (eq *eqchecker) checkValue(v, w reflect.Value) error {
 	return nil
 }
 
-// diff returns the output of running diff on b1 and b2.
-func diff(b1, b2 []byte) (data []byte, err error) {
-	f1, err := ioutil.TempFile("", "testdiff")
-	if err != nil {
-		return nil, err
-	}
-	defer os.Remove(f1.Name())
-	defer f1.Close()
-
-	f2, err := ioutil.TempFile("", "testdiff")
-	if err != nil {
-		return nil, err
-	}
-	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
-}
-
 // tdiff logs the diff output to t.Error.
 func tdiff(t *testing.T, a, b string) {
-	data, err := diff([]byte(a), []byte(b))
+	data, err := diff.Diff("modfile-test", []byte(a), []byte(b))
 	if err != nil {
 		t.Error(err)
 		return
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)
 	}
diff --git a/src/cmd/internal/diff/diff.go b/src/cmd/internal/diff/diff.go
new file mode 100644
index 0000000000..e9d2c23780
--- /dev/null
+++ b/src/cmd/internal/diff/diff.go
@@ -0,0 +1,58 @@
+// Copyright 2019 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 diff implements a Diff function that compare two inputs
+// using the 'diff' tool.
+package diff
+
+import (
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"runtime"
+)
+
+// Returns diff of two arrays of bytes in diff tool format.
+func Diff(prefix string, b1, b2 []byte) ([]byte, error) {
+	f1, err := writeTempFile(prefix, b1)
+	if err != nil {
+		return nil, err
+	}
+	defer os.Remove(f1)
+
+	f2, err := writeTempFile(prefix, b2)
+	if err != nil {
+		return nil, err
+	}
+	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 data, err
+}
+
+func writeTempFile(prefix string, data []byte) (string, error) {
+	file, err := ioutil.TempFile("", 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
+}