}
	}
	return nil
}

// walk recursively descends path, calling walkFn.
func walk(path string, info fs.FileInfo, walkFn WalkFunc) error {
	if !info.IsDir() {
		return walkFn(path, info, nil)
	}

	names, err := readDirNames(path)
	err1 := walkFn(path, info, err)
	// If err != nil, walk can't walk into this directory.
	// err1 != nil means walkFn want walk to skip this directory or stop walking.

		if err := walk(filename, fi, walkFn); err != nil {
			if !fi.IsDir() || err != filepath.SkipDir {
				return err
			}
		}
	}
	return nil
}

// Walk walks the file tree rooted at root, calling walkFn for each file or
// directory in the tree, including root.
func Walk(root string, walkFn filepath.WalkFunc) error {
	Trace("Walk", root)
	info, err := Lstat(root)
	if err != nil {

// ReadDir via os.ReadDir
func (fs *DefaultFs) ReadDir(dirname string) ([]os.DirEntry, error) {
	return os.ReadDir(fs.prefix(dirname))
}

// Walk via filepath.Walk
func (fs *DefaultFs) Walk(root string, walkFn filepath.WalkFunc) error {
	return filepath.Walk(fs.prefix(root), walkFn)
}

// defaultFile implements File using same-named functions from "os"
type defaultFile struct {
	file *os.File
}

		count++
		return false
	})
	return count
}

// WalkFn is used when walking the tree. Takes a
// key and value, returning if iteration should
// be terminated.
type WalkFn[T any] func(s netip.Prefix, v T) bool

// DepthFirstWalk is used to walk the tree of the corresponding IP family
func (t *Tree[T]) DepthFirstWalk(isIPv6 bool, fn WalkFn[T]) {
	if isIPv6 {
		recursiveWalk(t.rootV6, fn)
	}

	// from "os"
	ReadFile(filename string) ([]byte, error)
	TempDir(dir, prefix string) (string, error)
	TempFile(dir, prefix string) (File, error)
	ReadDir(dirname string) ([]os.DirEntry, error)
	Walk(root string, walkFn filepath.WalkFunc) error
}

// File is an interface that we can use to mock various filesystem operations typically
// accessed through the File object from the "os" package
type File interface {

		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")
		}
	}

	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"))
	})

func listStdPkgs(goroot string) ([]string, error) {
	// Based on cmd/go's matchPackages function.
	var pkgs []string

	src := filepath.Join(goroot, "src") + string(filepath.Separator)
	walkFn := func(path string, d fs.DirEntry, err error) error {
		if err != nil || !d.IsDir() || path == src {
			return nil
		}

		base := filepath.Base(path)

			var got []string

			err := Walk(tc.dir, func(path string, info fs.FileInfo, err error) error {
				t.Logf("walk %q", path)
				got = append(got, path)
				if err != nil {
					t.Errorf("walkfn: got non nil err argument: %v, want nil err argument", err)
				}
				return nil
			})
			if err != nil {
				t.Errorf("Walk: got error %q, want nil", err)
			}

// walked multiple times.
// TODO(gri) Revisit this design. It may make sense to walk those nodes
// only once. A place where this matters is types2.TestResolveIdents.
func Walk(root Node, v Visitor) {
	walker{v}.node(root)
}

// A Visitor's Visit method is invoked for each node encountered by Walk.
// If the result visitor w is not nil, Walk visits each of the children

				break
			}
			return err
		}
	}
	return nil
}

// WalkDir walks the file tree rooted at root, calling fn for each file or
// directory in the tree, including root.
//
// All errors that arise visiting files and directories are filtered by fn:
// see the [fs.WalkDirFunc] documentation for details.
//
// The files are walked in lexical order, which makes the output deterministic