func xremoveall(p string) {
	if vflag > 2 {
		errprintf("rm -r %s\n", p)
	}
	os.RemoveAll(p)
}

// xreaddir replaces dst with a list of the names of the files and subdirectories in dir.
// The names are relative to dir; they are not full paths.
func xreaddir(dir string) []string {
	f, err := os.Open(dir)
	if err != nil {
		fatalf("%v", err)
	}
	defer f.Close()

		xmkdir(p)
	}

	goosGoarch := pathf("%s/pkg/%s_%s", goroot, gohostos, gohostarch)
	if rebuildall {
		xremoveall(goosGoarch)
	}
	xmkdirall(goosGoarch)
	xatexit(func() {
		if files := xreaddir(goosGoarch); len(files) == 0 {
			xremove(goosGoarch)
		}
	})

	if goos != gohostos || goarch != gohostarch {
		p := pathf("%s/pkg/%s_%s", goroot, goos, goarch)
		if rebuildall {
			xremoveall(p)
		}

// that provides an optimized implementation of [ReadDir].
type ReadDirFS interface {
	FS

	// ReadDir reads the named directory
	// and returns a list of directory entries sorted by filename.
	ReadDir(name string) ([]DirEntry, error)
}

// ReadDir reads the named directory
// and returns a list of directory entries sorted by filename.
//
// If fs implements [ReadDirFS], ReadDir calls fs.ReadDir.

func isDirEmpty(dirname string, legacy bool) bool {
	if legacy {
		// On filesystems such as btrfs, nfs this is not true, so fallback
		// to performing readdir() instead.
		entries, err := readDirN(dirname, 1)
		if err != nil {
			return false
		}
		return len(entries) == 0
	}
	var stat syscall.Stat_t
	if err := syscall.Stat(dirname, &stat); err != nil {
		return false
	}

	// Check non existent directory.
	if _, err := readDir("/tmp/non-existent-directory"); err != errFileNotFound {
		t.Fatalf("expected = %s, got: %s", errFileNotFound, err)
	}

	file := path.Join(os.TempDir(), "issue")
	if err := os.WriteFile(file, []byte(""), 0o644); err != nil {
		t.Fatal(err)
	}
	defer os.RemoveAll(file)

	// Check if file is given.
	if _, err := readDir(path.Join(file, "mydir")); err != errFileNotFound {

func (f *File) Readdir(n int) ([]FileInfo, error) {
	if f == nil {
		return nil, ErrInvalid
	}
	_, _, infos, err := f.readdir(n, readdirFileInfo)
	if infos == nil {
		// Readdir has historically always returned a non-nil empty slice, never nil,
		// even on error (except misuse with nil receiver above).
		// Keep it that way to avoid breaking overly sensitive callers.
		infos = []FileInfo{}
	}
	return infos, err
}

			d.bufp, d.nbuf = 0, nb

			if err != nil {
				if err == io.EOF {
					break
				}
				return names, dirents, infos, &PathError{Op: "readdir", Path: file.name, Err: err}
			}
			if nb < syscall.STATFIXLEN {
				return names, dirents, infos, &PathError{Op: "readdir", Path: file.name, Err: syscall.ErrShortStat}
			}
		}

		// Get a record from the buffer.
		b := d.buf[d.bufp:]

			t.errorf("%s: third Open: ReadDir(%d) after %d: 0 entries but nil error", dir, n, len(list2))
			return
		}
	}
	t.checkDirList(dir, "first Open+ReadDir(-1) vs third Open+ReadDir(1,2) loop", list, list2)

	// If fsys has ReadDir, check that it matches and is sorted.
	if fsys, ok := t.fsys.(fs.ReadDirFS); ok {
		list2, err := fsys.ReadDir(dir)
		if err != nil {
			t.errorf("%s: fsys.ReadDir: %w", dir, err)
			return
		}

				names = append(names, d.Name())
			}
			t.Errorf("ReadDir(%s) = %v, %v, want %v, nil", desc, names, err, []string{"hello.txt", "sub"})
		}
	}

	// Test that ReadDir uses the method when present.
	dirs, err := ReadDir(readDirOnly{testFsys}, ".")
	check("readDirOnly", dirs, err)

	// Test that ReadDir uses Open when the method is not present.
	dirs, err = ReadDir(openOnly{testFsys}, ".")
	check("openOnly", dirs, err)

	}
}

func TestReadDir(t *testing.T) {
	dirname := "rumpelstilzchen"
	_, err := ReadDir(dirname)
	if err == nil {
		t.Fatalf("ReadDir %s: error expected, none found", dirname)
	}

	dirname = ".."
	list, err := ReadDir(dirname)
	if err != nil {
		t.Fatalf("ReadDir %s: %v", dirname, err)
	}

	foundFile := false
	foundSubDir := false
	for _, dir := range list {
		switch {