i--
	}
	if i < 0 {
		return ".", name, isDir
	}
	return name[:i], name[i+1:], isDir
}

var dotFile = &fileListEntry{name: "./", isDir: true}

func (r *Reader) openLookup(name string) *fileListEntry {
	if name == "." {
		return dotFile
	}

	dir, elem, _ := split(name)
	files := r.fileList
	i := sort.Search(len(files), func(i int) bool {
		idir, ielem, _ := split(files[i].name)

func (fi headerFileInfo) Size() int64 {
	if fi.fh.UncompressedSize64 > 0 {
		return int64(fi.fh.UncompressedSize64)
	}
	return int64(fi.fh.UncompressedSize)
}
func (fi headerFileInfo) IsDir() bool { return fi.Mode().IsDir() }
func (fi headerFileInfo) ModTime() time.Time {
	if fi.fh.Modified.IsZero() {
		return fi.fh.ModTime()
	}
	return fi.fh.Modified.UTC()
}

func (fi headerFileInfo) Size() int64        { return fi.h.Size }
func (fi headerFileInfo) IsDir() bool        { return fi.Mode().IsDir() }
func (fi headerFileInfo) ModTime() time.Time { return fi.h.ModTime }
func (fi headerFileInfo) Sys() any           { return fi.h }

// Name returns the base name of the file.
func (fi headerFileInfo) Name() string {
	if fi.IsDir() {
		return path.Base(path.Clean(fi.h.Name))
	}
	return path.Base(fi.h.Name)

func (tw *Writer) AddFS(fsys fs.FS) error {
	return fs.WalkDir(fsys, ".", func(name string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}
		info, err := d.Info()
		if err != nil {
			return err
		}
		// TODO(#49580): Handle symlinks when fs.ReadLinkFS is available.
		if !info.Mode().IsRegular() {

		if err != nil {
			t.Error(err)
			continue
		}
		if strings.Contains(fi.Name(), "/") {
			t.Errorf("FileInfo of %q contains slash: %q", v.h.Name, fi.Name())
		}
		name := path.Base(v.h.Name)
		if fi.IsDir() {
			name += "/"
		}
		if got, want := h2.Name, name; got != want {
			t.Errorf("i=%d: Name: got %v, want %v", i, got, want)
		}
		if got, want := h2.Size, v.h.Size; got != want {

pkg os, method (*PathError) Unwrap() error
pkg os, method (FileMode) IsDir() bool
pkg os, method (FileMode) IsRegular() bool
pkg os, method (FileMode) Perm() FileMode
pkg os, method (FileMode) String() string
pkg os, type FileInfo interface { IsDir, ModTime, Mode, Name, Size, Sys }
pkg os, type FileInfo interface, IsDir() bool
pkg os, type FileInfo interface, ModTime() time.Time

func (w *Writer) AddFS(fsys fs.FS) error {
	return fs.WalkDir(fsys, ".", func(name string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}
		info, err := d.Info()
		if err != nil {
			return err
		}
		if !info.Mode().IsRegular() {
			return errors.New("zip: cannot add non-regular file")
		}

	}

	d, err := os.Open(src)
	if err != nil {
		return err
	}
	defer d.Close()
	fi, err := d.Readdir(-1)
	if err != nil {
		return err
	}

	for _, f := range fi {
		if f.IsDir() {
			if f.Name() == "testdata" {
				if err := cp(dst, filepath.Join(src, f.Name())); err != nil {
					return err
				}
			}
			continue
		}

	w.imported[name] = &importing

	// Determine package files.
	dir := w.importDir[name]
	if dir == "" {
		dir = filepath.Join(w.root, filepath.FromSlash(name))
	}
	if fi, err := os.Stat(dir); err != nil || !fi.IsDir() {
		log.Panicf("no source in tree for import %q (from import %s in %s): %v", name, fromPath, fromDir, err)
	}

	context := w.context
	if context == nil {
		context = &build.Default
	}

	tr := NewReader(&buf)

	entries, err := fsys.ReadDir(".")
	if err != nil {
		t.Fatal(err)
	}

	var curfname string
	for _, entry := range entries {
		curfname = entry.Name()
		if entry.IsDir() {
			curfname += "/"
			continue
		}
		hdr, err := tr.Next()
		if err == io.EOF {
			break // End of archive
		}
		if err != nil {
			t.Fatal(err)
		}