path/filepath: add WalkDir

WalkDir is like Walk but can use ReadDir to read directories,
instead of Readdirnames + Lstat on every entry,
which is usually a significant performance improvement.
(The Lstat can still happen if the walk function calls d.Info.)

Fixes #42027.

[Replay of CL 266240 after it was reverted due to accidentally
enabling on Windows a test that does not work on Windows.
The original code only ran the test on os.Getuid() > 0.
The rolled-back CL skipped the test on os.Getuid() == 0.
But on Windows, os.Getuid(), it turns out, always returns -1.
So what looked like a test for root was also excluding Windows.
This CL revises the test to skip Windows explicitly.]

Change-Id: I9b3661013d6449b7486532445d934ae91e5393ef
Reviewed-on: https://go-review.googlesource.com/c/go/+/267887
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

1 files changed, 62 insertions, 30 deletions

diff --git a/src/path/filepath/path_test.go b/src/path/filepath/path_test.go
index 7dc8b60c28..ec6f8f2de9 100644
--- a/src/path/filepath/path_test.go
+++ b/src/path/filepath/path_test.go
@@ -394,8 +394,8 @@ func checkMarks(t *testing.T, report bool) {
 // Assumes that each node name is unique. Good enough for a test.
 // If clear is true, any incoming error is cleared before return. The errors
 // are always accumulated, though.
-func mark(info fs.FileInfo, err error, errors *[]error, clear bool) error {
-	name := info.Name()
+func mark(d fs.DirEntry, err error, errors *[]error, clear bool) error {
+	name := d.Name()
 	walkTree(tree, tree.name, func(path string, n *Node) {
 		if n.name == name {
 			n.mark++
@@ -432,6 +432,19 @@ func chtmpdir(t *testing.T) (restore func()) {
 }
 
 func TestWalk(t *testing.T) {
+	walk := func(root string, fn filepath.WalkDirFunc) error {
+		return filepath.Walk(root, func(path string, info fs.FileInfo, err error) error {
+			return fn(path, &filepath.DirEntryFromInfo{info}, err)
+		})
+	}
+	testWalk(t, walk, 1)
+}
+
+func TestWalkDir(t *testing.T) {
+	testWalk(t, filepath.WalkDir, 2)
+}
+
+func testWalk(t *testing.T, walk func(string, filepath.WalkDirFunc) error, errVisit int) {
 	if runtime.GOOS == "ios" {
 		restore := chtmpdir(t)
 		defer restore()
@@ -455,11 +468,11 @@ func TestWalk(t *testing.T) {
 	makeTree(t)
 	errors := make([]error, 0, 10)
 	clear := true
-	markFn := func(path string, info fs.FileInfo, err error) error {
-		return mark(info, err, &errors, clear)
+	markFn := func(path string, d fs.DirEntry, err error) error {
+		return mark(d, err, &errors, clear)
 	}
 	// Expect no errors.
-	err = filepath.Walk(tree.name, markFn)
+	err = walk(tree.name, markFn)
 	if err != nil {
 		t.Fatalf("no error expected, found: %s", err)
 	}
@@ -469,10 +482,20 @@ func TestWalk(t *testing.T) {
 	checkMarks(t, true)
 	errors = errors[0:0]
 
-	// Test permission errors. Only possible if we're not root
-	// and only on some file systems (AFS, FAT).  To avoid errors during
-	// all.bash on those file systems, skip during go test -short.
-	if os.Getuid() > 0 && !testing.Short() {
+	t.Run("PermErr", func(t *testing.T) {
+		// Test permission errors. Only possible if we're not root
+		// and only on some file systems (AFS, FAT).  To avoid errors during
+		// all.bash on those file systems, skip during go test -short.
+		if runtime.GOOS == "windows" {
+			t.Skip("skipping on Windows")
+		}
+		if os.Getuid() == 0 {
+			t.Skip("skipping as root")
+		}
+		if testing.Short() {
+			t.Skip("skipping in short mode")
+		}
+
 		// introduce 2 errors: chmod top-level directories to 0
 		os.Chmod(filepath.Join(tree.name, tree.entries[1].name), 0)
 		os.Chmod(filepath.Join(tree.name, tree.entries[3].name), 0)
@@ -482,9 +505,9 @@ func TestWalk(t *testing.T) {
 		markTree(tree.entries[1])
 		markTree(tree.entries[3])
 		// correct double-marking of directory itself
-		tree.entries[1].mark--
-		tree.entries[3].mark--
-		err := filepath.Walk(tree.name, markFn)
+		tree.entries[1].mark -= errVisit
+		tree.entries[3].mark -= errVisit
+		err := walk(tree.name, markFn)
 		if err != nil {
 			t.Fatalf("expected no error return from Walk, got %s", err)
 		}
@@ -500,10 +523,10 @@ func TestWalk(t *testing.T) {
 		markTree(tree.entries[1])
 		markTree(tree.entries[3])
 		// correct double-marking of directory itself
-		tree.entries[1].mark--
-		tree.entries[3].mark--
+		tree.entries[1].mark -= errVisit
+		tree.entries[3].mark -= errVisit
 		clear = false // error will stop processing
-		err = filepath.Walk(tree.name, markFn)
+		err = walk(tree.name, markFn)
 		if err == nil {
 			t.Fatalf("expected error return from Walk")
 		}
@@ -517,7 +540,7 @@ func TestWalk(t *testing.T) {
 		// restore permissions
 		os.Chmod(filepath.Join(tree.name, tree.entries[1].name), 0770)
 		os.Chmod(filepath.Join(tree.name, tree.entries[3].name), 0770)
-	}
+	})
 }
 
 func touch(t *testing.T, name string) {
@@ -544,7 +567,7 @@ func TestWalkSkipDirOnFile(t *testing.T) {
 	touch(t, filepath.Join(td, "dir/foo2"))
 
 	sawFoo2 := false
-	walker := func(path string, info fs.FileInfo, err error) error {
+	walker := func(path string) error {
 		if strings.HasSuffix(path, "foo2") {
 			sawFoo2 = true
 		}
@@ -553,22 +576,31 @@ func TestWalkSkipDirOnFile(t *testing.T) {
 		}
 		return nil
 	}
+	walkFn := func(path string, _ fs.FileInfo, _ error) error { return walker(path) }
+	walkDirFn := func(path string, _ fs.DirEntry, _ error) error { return walker(path) }
 
-	err = filepath.Walk(td, walker)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if sawFoo2 {
-		t.Errorf("SkipDir on file foo1 did not block processing of foo2")
+	check := func(t *testing.T, walk func(root string) error, root string) {
+		t.Helper()
+		sawFoo2 = false
+		err = walk(root)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if sawFoo2 {
+			t.Errorf("SkipDir on file foo1 did not block processing of foo2")
+		}
 	}
 
-	err = filepath.Walk(filepath.Join(td, "dir"), walker)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if sawFoo2 {
-		t.Errorf("SkipDir on file foo1 did not block processing of foo2")
-	}
+	t.Run("Walk", func(t *testing.T) {
+		Walk := func(root string) error { return filepath.Walk(td, walkFn) }
+		check(t, Walk, td)
+		check(t, Walk, filepath.Join(td, "dir"))
+	})
+	t.Run("WalkDir", func(t *testing.T) {
+		WalkDir := func(root string) error { return filepath.WalkDir(td, walkDirFn) }
+		check(t, WalkDir, td)
+		check(t, WalkDir, filepath.Join(td, "dir"))
+	})
 }
 
 func TestWalkFileError(t *testing.T) {