io/fs, path/filepath: honor SkipDir on second WalkDirFunc error call

Fixes #51617

Change-Id: I03e9e575d9bad1481e7e4f051b50a077ba5f2fe0
Reviewed-on: https://go-review.googlesource.com/c/go/+/392154
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>

2 files changed, 36 insertions, 0 deletions

diff --git a/src/io/fs/walk.go b/src/io/fs/walk.go
index 534876bad3..52a51bbd37 100644
--- a/src/io/fs/walk.go
+++ b/src/io/fs/walk.go
@@ -76,6 +76,9 @@ func walkDir(fsys FS, name string, d DirEntry, walkDirFn WalkDirFunc) error {
 		// Second call, to report ReadDir error.
 		err = walkDirFn(name, d, err)
 		if err != nil {
+			if err == SkipDir && d.IsDir() {
+				err = nil
+			}
 			return err
 		}
 	}
diff --git a/src/io/fs/walk_test.go b/src/io/fs/walk_test.go
index 5e127e71cd..04358beb24 100644
--- a/src/io/fs/walk_test.go
+++ b/src/io/fs/walk_test.go
@@ -8,6 +8,8 @@ import (
 	. "io/fs"
 	"os"
 	pathpkg "path"
+	"path/filepath"
+	"reflect"
 	"testing"
 	"testing/fstest"
 )
@@ -122,3 +124,34 @@ func TestWalkDir(t *testing.T) {
 	}
 	checkMarks(t, true)
 }
+
+func TestIssue51617(t *testing.T) {
+	dir := t.TempDir()
+	for _, sub := range []string{"a", filepath.Join("a", "bad"), filepath.Join("a", "next")} {
+		if err := os.Mkdir(filepath.Join(dir, sub), 0755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	bad := filepath.Join(dir, "a", "bad")
+	if err := os.Chmod(bad, 0); err != nil {
+		t.Fatal(err)
+	}
+	defer os.Chmod(bad, 0700) // avoid errors on cleanup
+	var saw []string
+	err := WalkDir(os.DirFS(dir), ".", func(path string, d DirEntry, err error) error {
+		if err != nil {
+			return filepath.SkipDir
+		}
+		if d.IsDir() {
+			saw = append(saw, path)
+		}
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []string{".", "a", "a/bad", "a/next"}
+	if !reflect.DeepEqual(saw, want) {
+		t.Errorf("got directories %v, want %v", saw, want)
+	}
+}