io/fs: add WalkDir

This commit is a copy of filepath.WalkDir adapted to use fs.FS
instead of the native OS file system. It is the last implementation
piece of the io/fs proposal.

The original io/fs proposal was to adopt filepath.Walk, but we
have since introduced the more efficient filepath.WalkDir (#42027),
so this CL adopts that more efficient option instead.

(The changes in path/filepath bring the two copies more in line
with each other. The main change is unembedding the field
in statDirEntry, so that the fs.DirEntry passed to the WalkDirFunc
for the root of the tree does not have any extra methods.)

For #41190.

Change-Id: I9359dfcc110338c0ec64535f22cafb38d0b613a6
Reviewed-on: https://go-review.googlesource.com/c/go/+/243916
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

1 files changed, 12 insertions, 3 deletions

diff --git a/src/path/filepath/path_test.go b/src/path/filepath/path_test.go
index ec6f8f2de9..d760530e26 100644
--- a/src/path/filepath/path_test.go
+++ b/src/path/filepath/path_test.go
@@ -432,19 +432,28 @@ func chtmpdir(t *testing.T) (restore func()) {
 }
 
 func TestWalk(t *testing.T) {
-	walk := func(root string, fn filepath.WalkDirFunc) error {
+	walk := func(root string, fn fs.WalkDirFunc) error {
 		return filepath.Walk(root, func(path string, info fs.FileInfo, err error) error {
-			return fn(path, &filepath.DirEntryFromInfo{info}, err)
+			return fn(path, &statDirEntry{info}, err)
 		})
 	}
 	testWalk(t, walk, 1)
 }
 
+type statDirEntry struct {
+	info fs.FileInfo
+}
+
+func (d *statDirEntry) Name() string               { return d.info.Name() }
+func (d *statDirEntry) IsDir() bool                { return d.info.IsDir() }
+func (d *statDirEntry) Type() fs.FileMode          { return d.info.Mode().Type() }
+func (d *statDirEntry) Info() (fs.FileInfo, error) { return d.info, nil }
+
 func TestWalkDir(t *testing.T) {
 	testWalk(t, filepath.WalkDir, 2)
 }
 
-func testWalk(t *testing.T, walk func(string, filepath.WalkDirFunc) error, errVisit int) {
+func testWalk(t *testing.T, walk func(string, fs.WalkDirFunc) error, errVisit int) {
 	if runtime.GOOS == "ios" {
 		restore := chtmpdir(t)
 		defer restore()