// 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 (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
		}

	//
	// If n > 0, ReadDir returns at most n DirEntry structures.
	// In this case, if ReadDir returns an empty slice, it will return
	// a non-nil error explaining why.
	// At the end of a directory, the error is io.EOF.
	// (ReadDir must return io.EOF itself, not an error wrapping io.EOF.)
	//
	// If n <= 0, ReadDir returns all the DirEntry values from the directory

// attempted and has err set to nil, giving the function a chance to
// return [SkipDir] or [SkipAll] and avoid the ReadDir entirely. The second call
// is after a failed ReadDir and reports the error from ReadDir.
// (If ReadDir succeeds, there is no second call.)
//
// The differences between WalkDirFunc compared to [path/filepath.WalkFunc] are:
//
//   - The second argument has type [DirEntry] instead of [FileInfo].

	}
}

func TestReadDir(t *testing.T) {
	t.Parallel()

	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 {

	return os.WriteFile(filename, data, perm)
}

// ReadDir reads the directory named by dirname and returns
// a list of fs.FileInfo for the directory's contents,
// sorted by filename. If an error occurs reading the directory,
// ReadDir returns no directory entries along with the error.
//
// Deprecated: As of Go 1.16, [os.ReadDir] is a more efficient and correct choice:

	return syscall.Chdir(fd.Path)
}

// ReadDir wraps syscall.ReadDir.
// We treat this like an ordinary system call rather than a call
// that tries to fill the buffer.
func (fd *FD) ReadDir(buf []byte, cookie syscall.Dircookie) (int, error) {
	if err := fd.incref(); err != nil {
		return 0, err
	}
	defer fd.decref()
	for {
		n, err := syscall.ReadDir(fd.Sysfd, buf, cookie)
		if err != nil {
			n = 0

			if IsNotExist(err) {
				// File disappeared between readdir and stat.
				// Treat as if it didn't exist.
				continue
			}
			if err != nil {
				return nil, dirents, nil, err
			}
			dirents = append(dirents, de)
		} else {
			info, err := lstat(f.name + "/" + string(name))
			if IsNotExist(err) {
				// File disappeared between readdir + stat.
				// Treat as if it didn't exist.
				continue
			}