}
		in = f
		defer func() {
			f.Close()
			<-fdSem
		}()
	}

	// Compute the file's size and read its contents with minimal allocations.
	//
	// If we have the FileInfo from filepath.WalkDir, use it to make
	// a buffer of the right size and avoid ReadAll's reallocations.
	//
	// If the size is unknown (or bogus, or overflows an int), fall back to
	// a size-independent ReadAll.
	size := -1

		// After go 1.16, WalkDir was introduced, it's more effective than Walk because the callback WalkDirFunc is called before
		// reading a directory, making it save some time when a container's subPath contains lots of dirs.
		// See https://github.com/kubernetes/kubernetes/pull/71804 and https://github.com/kubernetes/kubernetes/issues/107667 for more details.

			base.Fatalf("download %s: %v", gotoolchain, err)
		}
		if info.Mode()&0111 == 0 {
			// allowExec sets the exec permission bits on all files found in dir.
			allowExec := func(dir string) {
				err := filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
					if err != nil {
						return err
					}
					if !d.IsDir() {
						info, err := os.Stat(path)
						if err != nil {
							return err
						}

	fmt.Fprintf(w, "For an overview of the script language, see <a href=\"/help\">/help</a>.\n\n")

	fmt.Fprintf(w, "<b>cache</b>\n")

	tw := tabwriter.NewWriter(w, 1, 8, 1, '\t', 0)
	err := filepath.WalkDir(s.scriptDir, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if filepath.Ext(path) != ".txt" {
			return nil
		}

		rel, err := filepath.Rel(s.scriptDir, path)

		readers[i] = newMetacacheReader(r)
		d := disks[i]

		// Send request to each disk.
		go func() {
			var werr error
			if d == nil {
				werr = errDiskNotFound
			} else {
				werr = d.WalkDir(ctx, WalkDirOptions{
					Limit:          opts.perDiskLimit,
					Bucket:         opts.bucket,
					BaseDir:        opts.path,
					Recursive:      opts.recursive,
					ReportNotFound: opts.reportNotFound,

		res = append(res, b)
	}
	// Remove empty headings at the end of the document.
	rem(1)
	return res
}

func sortedMarkdownFilenames(fsys fs.FS) ([]string, error) {
	var filenames []string
	err := fs.WalkDir(fsys, ".", func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if !d.IsDir() && strings.HasSuffix(path, ".md") {
			filenames = append(filenames, path)
		}
		return nil

			// contains nested modules this could push a lot of unnecessary contents,
			// but for the golang.org/x repos it seems to be significantly (~2x)
			// faster than copying one file at a time (via filepath.WalkDir),
			// apparently due to high latency in 'adb' commands.
			if err := adb("push", modDir, deviceModDir); err != nil {
				return 0, err
			}
		} else {

// and its transitive contents.
func makeDirsReadOnly(dir string) {
	type pathMode struct {
		path string
		mode fs.FileMode
	}
	var dirs []pathMode // in lexical order
	filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
		if err == nil && d.IsDir() {
			info, err := d.Info()
			if err == nil && info.Mode()&0222 != 0 {
				dirs = append(dirs, pathMode{path, info.Mode()})
			}

	switch name {
	case "opticks":
		var err error
		data, err = os.ReadFile("../../testdata/Isaac.Newton-Opticks.txt")
		if err != nil {
			return nil, err
		}
	case "go":
		err := filepath.WalkDir("../..", func(path string, info fs.DirEntry, err error) error {
			if err == nil && strings.HasSuffix(path, ".go") && !info.IsDir() {
				file, err := os.ReadFile(path)
				if err != nil {
					return err
				}

		if name == "builtin" || name == "cmd" {
			return filepath.SkipDir
		}

		pkgs = append(pkgs, strings.TrimPrefix(name, "vendor/"))
		return nil
	}
	if err := filepath.WalkDir(src, walkFn); err != nil {
		return nil, err
	}
	return pkgs, nil
}

func TestDependencies(t *testing.T) {
	if !testenv.HasSrc() {
		// Tests run in a limited file system and we do not