[release-branch.go1.16] archive/zip: only return directory once via io/fs.FS

While we're here fix the ModTime value for directories.

For #43872
For #45345
Fixes #45347

Change-Id: I155e6517713ef6a9482b9431f1167a44337c6ad2
Reviewed-on: https://go-review.googlesource.com/c/go/+/311530
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
(cherry picked from commit 87e4dcd446df2ab1985ef61ce15da329493248a1)
Reviewed-on: https://go-review.googlesource.com/c/go/+/315249
Trust: Jeremy Faller <jeremy@golang.org>

3 files changed, 92 insertions, 18 deletions

diff --git a/src/archive/zip/reader.go b/src/archive/zip/reader.go
index c288ad965b..18f9833db0 100644
--- a/src/archive/zip/reader.go
+++ b/src/archive/zip/reader.go
@@ -628,10 +628,11 @@ func (b *readBuf) sub(n int) readBuf {
 }
 
 // A fileListEntry is a File and its ename.
-// If file == nil, the fileListEntry describes a directory, without metadata.
+// If file == nil, the fileListEntry describes a directory without metadata.
 type fileListEntry struct {
-	name string
-	file *File // nil for directories
+	name  string
+	file  *File
+	isDir bool
 }
 
 type fileInfoDirEntry interface {
@@ -640,20 +641,26 @@ type fileInfoDirEntry interface {
 }
 
 func (e *fileListEntry) stat() fileInfoDirEntry {
-	if e.file != nil {
+	if !e.isDir {
 		return headerFileInfo{&e.file.FileHeader}
 	}
 	return e
 }
 
 // Only used for directories.
-func (f *fileListEntry) Name() string       { _, elem, _ := split(f.name); return elem }
-func (f *fileListEntry) Size() int64        { return 0 }
-func (f *fileListEntry) ModTime() time.Time { return time.Time{} }
-func (f *fileListEntry) Mode() fs.FileMode  { return fs.ModeDir | 0555 }
-func (f *fileListEntry) Type() fs.FileMode  { return fs.ModeDir }
-func (f *fileListEntry) IsDir() bool        { return true }
-func (f *fileListEntry) Sys() interface{}   { return nil }
+func (f *fileListEntry) Name() string      { _, elem, _ := split(f.name); return elem }
+func (f *fileListEntry) Size() int64       { return 0 }
+func (f *fileListEntry) Mode() fs.FileMode { return fs.ModeDir | 0555 }
+func (f *fileListEntry) Type() fs.FileMode { return fs.ModeDir }
+func (f *fileListEntry) IsDir() bool       { return true }
+func (f *fileListEntry) Sys() interface{}  { return nil }
+
+func (f *fileListEntry) ModTime() time.Time {
+	if f.file == nil {
+		return time.Time{}
+	}
+	return f.file.FileHeader.Modified.UTC()
+}
 
 func (f *fileListEntry) Info() (fs.FileInfo, error) { return f, nil }
 
@@ -673,15 +680,32 @@ func toValidName(name string) string {
 func (r *Reader) initFileList() {
 	r.fileListOnce.Do(func() {
 		dirs := make(map[string]bool)
+		knownDirs := make(map[string]bool)
 		for _, file := range r.File {
+			isDir := len(file.Name) > 0 && file.Name[len(file.Name)-1] == '/'
 			name := toValidName(file.Name)
 			for dir := path.Dir(name); dir != "."; dir = path.Dir(dir) {
 				dirs[dir] = true
 			}
-			r.fileList = append(r.fileList, fileListEntry{name, file})
+			entry := fileListEntry{
+				name:  name,
+				file:  file,
+				isDir: isDir,
+			}
+			r.fileList = append(r.fileList, entry)
+			if isDir {
+				knownDirs[name] = true
+			}
 		}
 		for dir := range dirs {
-			r.fileList = append(r.fileList, fileListEntry{dir + "/", nil})
+			if !knownDirs[dir] {
+				entry := fileListEntry{
+					name:  dir,
+					file:  nil,
+					isDir: true,
+				}
+				r.fileList = append(r.fileList, entry)
+			}
 		}
 
 		sort.Slice(r.fileList, func(i, j int) bool { return fileEntryLess(r.fileList[i].name, r.fileList[j].name) })
@@ -705,7 +729,7 @@ func (r *Reader) Open(name string) (fs.File, error) {
 	if e == nil || !fs.ValidPath(name) {
 		return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist}
 	}
-	if e.file == nil || strings.HasSuffix(e.file.Name, "/") {
+	if e.isDir {
 		return &openDir{e, r.openReadDir(name), 0}, nil
 	}
 	rc, err := e.file.Open()
@@ -730,7 +754,7 @@ func split(name string) (dir, elem string, isDir bool) {
 	return name[:i], name[i+1:], isDir
 }
 
-var dotFile = &fileListEntry{name: "./"}
+var dotFile = &fileListEntry{name: "./", isDir: true}
 
 func (r *Reader) openLookup(name string) *fileListEntry {
 	if name == "." {
diff --git a/src/archive/zip/reader_test.go b/src/archive/zip/reader_test.go
index 5faf1f49b5..c6e8d21568 100644
--- a/src/archive/zip/reader_test.go
+++ b/src/archive/zip/reader_test.go
@@ -1073,12 +1073,62 @@ func TestIssue12449(t *testing.T) {
 }
 
 func TestFS(t *testing.T) {
-	z, err := OpenReader("testdata/unix.zip")
+	for _, test := range []struct {
+		file string
+		want []string
+	}{
+		{
+			"testdata/unix.zip",
+			[]string{"hello", "dir/bar", "readonly"},
+		},
+		{
+			"testdata/subdir.zip",
+			[]string{"a/b/c"},
+		},
+	} {
+		t.Run(test.file, func(t *testing.T) {
+			t.Parallel()
+			z, err := OpenReader(test.file)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer z.Close()
+			if err := fstest.TestFS(z, test.want...); err != nil {
+				t.Error(err)
+			}
+		})
+	}
+}
+
+func TestFSModTime(t *testing.T) {
+	t.Parallel()
+	z, err := OpenReader("testdata/subdir.zip")
 	if err != nil {
 		t.Fatal(err)
 	}
-	if err := fstest.TestFS(z, "hello", "dir/bar", "dir/empty", "readonly"); err != nil {
-		t.Fatal(err)
+	defer z.Close()
+
+	for _, test := range []struct {
+		name string
+		want time.Time
+	}{
+		{
+			"a",
+			time.Date(2021, 4, 19, 12, 29, 56, 0, timeZone(-7*time.Hour)).UTC(),
+		},
+		{
+			"a/b/c",
+			time.Date(2021, 4, 19, 12, 29, 59, 0, timeZone(-7*time.Hour)).UTC(),
+		},
+	} {
+		fi, err := fs.Stat(z, test.name)
+		if err != nil {
+			t.Errorf("%s: %v", test.name, err)
+			continue
+		}
+		if got := fi.ModTime(); !got.Equal(test.want) {
+			t.Errorf("%s: got modtime %v, want %v", test.name, got, test.want)
+		}
 	}
 }
 
diff --git a/src/archive/zip/testdata/subdir.zip b/src/archive/zip/testdata/subdir.zip
new file mode 100644
index 0000000000..324d06b48d
--- /dev/null
+++ b/src/archive/zip/testdata/subdir.zip