Add Stat to finder/fs

Add a Stat method to finder/fs that will be used by finder to read
the mode of the target of a symlink.

Bug: 157656545
Test: fs_test.go
Change-Id: Ie2b4509b7d11857d9a1685de4477088b91d43c63

finder/fs/fs_test.go

@@ -0,0 +1,76 @@
+// Copyright 2020 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fs
+
+import (
+	"os"
+	"testing"
+)
+
+func TestMockFs_LstatStatSymlinks(t *testing.T) {
+	// setup filesystem
+	filesystem := NewMockFs(nil)
+	Create(t, "/tmp/realdir/hi.txt", filesystem)
+	Create(t, "/tmp/realdir/ignoreme.txt", filesystem)
+
+	Link(t, "/tmp/links/dir", "../realdir", filesystem)
+	Link(t, "/tmp/links/file", "../realdir/hi.txt", filesystem)
+	Link(t, "/tmp/links/broken", "nothingHere", filesystem)
+	Link(t, "/tmp/links/recursive", "recursive", filesystem)
+
+	assertStat := func(t *testing.T, stat os.FileInfo, err error, wantName string, wantMode os.FileMode) {
+		t.Helper()
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		if g, w := stat.Name(), wantName; g != w {
+			t.Errorf("want name %q, got %q", w, g)
+		}
+		if g, w := stat.Mode(), wantMode; g != w {
+			t.Errorf("%s: want mode %q, got %q", wantName, w, g)
+		}
+	}
+
+	assertErr := func(t *testing.T, err error, wantErr string) {
+		if err == nil || err.Error() != wantErr {
+			t.Errorf("want error %q, got %q", wantErr, err)
+		}
+	}
+
+	stat, err := filesystem.Lstat("/tmp/links/dir")
+	assertStat(t, stat, err, "dir", os.ModeSymlink)
+
+	stat, err = filesystem.Stat("/tmp/links/dir")
+	assertStat(t, stat, err, "realdir", os.ModeDir)
+
+	stat, err = filesystem.Lstat("/tmp/links/file")
+	assertStat(t, stat, err, "file", os.ModeSymlink)
+
+	stat, err = filesystem.Stat("/tmp/links/file")
+	assertStat(t, stat, err, "hi.txt", 0)
+
+	stat, err = filesystem.Lstat("/tmp/links/broken")
+	assertStat(t, stat, err, "broken", os.ModeSymlink)
+
+	stat, err = filesystem.Stat("/tmp/links/broken")
+	assertErr(t, err, "stat /tmp/links/nothingHere: file does not exist")
+
+	stat, err = filesystem.Lstat("/tmp/links/recursive")
+	assertStat(t, stat, err, "recursive", os.ModeSymlink)
+
+	stat, err = filesystem.Stat("/tmp/links/recursive")
+	assertErr(t, err, "read /tmp/links/recursive: too many levels of symbolic links")
+}