1 files changed, 67 insertions, 0 deletions
diff --git a/src/cmd/gofmt/gofmt_unix_test.go b/src/cmd/gofmt/gofmt_unix_test.go
new file mode 100644
index 0000000000..45b9234312
--- /dev/null
+++ b/src/cmd/gofmt/gofmt_unix_test.go
@@ -0,0 +1,67 @@
+// Copyright 2023 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.
+
+//go:build unix
+
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestPermissions(t *testing.T) {
+	if os.Getuid() == 0 {
+		t.Skip("skipping permission test when running as root")
+	}
+
+	dir := t.TempDir()
+	fn := filepath.Join(dir, "perm.go")
+
+	// Create a file that needs formatting without write permission.
+	if err := os.WriteFile(filepath.Join(fn), []byte("  package main"), 0o400); err != nil {
+		t.Fatal(err)
+	}
+
+	// Set mtime of the file in the past.
+	past := time.Now().Add(-time.Hour)
+	if err := os.Chtimes(fn, past, past); err != nil {
+		t.Fatal(err)
+	}
+
+	info, err := os.Stat(fn)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer func() { *write = false }()
+	*write = true
+
+	initParserMode()
+	initRewrite()
+
+	const maxWeight = 2 << 20
+	var buf, errBuf strings.Builder
+	s := newSequencer(maxWeight, &buf, &errBuf)
+	s.Add(fileWeight(fn, info), func(r *reporter) error {
+		return processFile(fn, info, nil, r)
+	})
+	if errBuf.Len() > 0 {
+		t.Log(errBuf)
+	}
+	if s.GetExitCode() == 0 {
+		t.Fatal("rewrite of read-only file succeeded unexpectedly")
+	}
+
+	info, err = os.Stat(fn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !info.ModTime().Equal(past) {
+		t.Errorf("after rewrite mod time is %v, want %v", info.ModTime(), past)
+	}
+}