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// 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 (
"bytes"
exec "internal/execabs"
"io/ioutil"
"os"
"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
}
// If we are on Windows and the diff is Cygwin diff,
// machines can get into a state where every Cygwin
// command works fine but prints a useless message like:
//
// Cygwin WARNING:
// Couldn't compute FAST_CWD pointer. This typically occurs if you're using
// an older Cygwin version on a newer Windows. Please update to the latest
// available Cygwin version from https://cygwin.com/. If the problem persists,
// please see https://cygwin.com/problems.html
//
// Skip over that message and just return the actual diff.
if len(data) > 0 && !bytes.HasPrefix(data, []byte("--- ")) {
i := bytes.Index(data, []byte("\n--- "))
if i >= 0 && i < 80*10 && bytes.Contains(data[:i], []byte("://cygwin.com/")) {
data = data[i+1:]
}
}
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
}
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