update resolveSymlinkAncestor and add tests

pkg/filesystem/resolve.go

@@ -125,8 +125,10 @@ func resolveSymlinkAncestor(path string) (string, error) {
 	if !filepath.IsAbs(path) {
 		return "", errors.New("dest path must be abs")
 	}
+
 	last := ""
 	newPath := path
+
 loop:
 	for newPath != "/" {
 		fi, err := os.Lstat(newPath)
@@ -134,11 +136,15 @@ loop:
 			return "", errors.Wrap(err, "failed to lstat")
 		}
 
-		switch mode := fi.Mode(); {
-		case mode&os.ModeSymlink != 0:
+		if util.IsSymlink(fi) {
 			last = filepath.Base(newPath)
 			newPath = filepath.Dir(newPath)
-		default:
+		} else {
+			// Even if the filenode pointed to by newPath is a regular file,
+			// one of its ancestors could be a symlink. We call filepath.EvalSymlinks
+			// to test whether there are any links in the path. If the output of
+			// EvalSymlinks is different than the input we know one of the nodes in the
+			// the path is a link.
 			target, err := filepath.EvalSymlinks(newPath)
 			if err != nil {
 				return "", err

pkg/filesystem/resolve_test.go

@@ -183,3 +183,196 @@ func Test_ResolvePaths(t *testing.T) {
 		validateResults(t, files, expectedFiles, err)
 	})
 }
+
+func Test_resolveSymlinkAncestor(t *testing.T) {
+	setupDirs := func(t *testing.T) (string, string) {
+		testDir, err := ioutil.TempDir("", "")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		targetDir := filepath.Join(testDir, "bar", "baz")
+
+		if err := os.MkdirAll(targetDir, 0777); err != nil {
+			t.Fatal(err)
+		}
+
+		targetPath := filepath.Join(targetDir, "bam.txt")
+
+		if err := ioutil.WriteFile(targetPath, []byte("meow"), 0777); err != nil {
+			t.Fatal(err)
+		}
+
+		return testDir, targetPath
+	}
+
+	t.Run("path is a symlink", func(t *testing.T) {
+		testDir, targetPath := setupDirs(t)
+		defer os.RemoveAll(testDir)
+
+		linkDir := filepath.Join(testDir, "foo", "buzz")
+
+		if err := os.MkdirAll(linkDir, 0777); err != nil {
+			t.Fatal(err)
+		}
+
+		linkPath := filepath.Join(linkDir, "zoom.txt")
+
+		if err := os.Symlink(targetPath, linkPath); err != nil {
+			t.Fatal(err)
+		}
+
+		expected := linkPath
+
+		actual, err := resolveSymlinkAncestor(linkPath)
+		if err != nil {
+			t.Errorf("expected err to be nil but was %s", err)
+		}
+
+		if actual != expected {
+			t.Errorf("expected result to be %s not %s", expected, actual)
+		}
+	})
+
+	t.Run("path is a dead symlink", func(t *testing.T) {
+		testDir, targetPath := setupDirs(t)
+		defer os.RemoveAll(testDir)
+
+		linkDir := filepath.Join(testDir, "foo", "buzz")
+
+		if err := os.MkdirAll(linkDir, 0777); err != nil {
+			t.Fatal(err)
+		}
+
+		linkPath := filepath.Join(linkDir, "zoom.txt")
+
+		if err := os.Symlink(targetPath, linkPath); err != nil {
+			t.Fatal(err)
+		}
+
+		if err := os.Remove(targetPath); err != nil {
+			t.Fatal(err)
+		}
+
+		expected := linkPath
+
+		actual, err := resolveSymlinkAncestor(linkPath)
+		if err != nil {
+			t.Errorf("expected err to be nil but was %s", err)
+		}
+
+		if actual != expected {
+			t.Errorf("expected result to be %s not %s", expected, actual)
+		}
+	})
+
+	t.Run("path is not a symlink", func(t *testing.T) {
+		testDir, targetPath := setupDirs(t)
+		defer os.RemoveAll(testDir)
+
+		expected := targetPath
+
+		actual, err := resolveSymlinkAncestor(targetPath)
+		if err != nil {
+			t.Errorf("expected err to be nil but was %s", err)
+		}
+
+		if actual != expected {
+			t.Errorf("expected result to be %s not %s", expected, actual)
+		}
+	})
+
+	t.Run("parent of path is a symlink", func(t *testing.T) {
+		testDir, targetPath := setupDirs(t)
+		defer os.RemoveAll(testDir)
+
+		targetDir := filepath.Dir(targetPath)
+
+		linkDir := filepath.Join(testDir, "foo")
+
+		if err := os.MkdirAll(linkDir, 0777); err != nil {
+			t.Fatal(err)
+		}
+
+		linkDir = filepath.Join(linkDir, "gaz")
+
+		if err := os.Symlink(targetDir, linkDir); err != nil {
+			t.Fatal(err)
+		}
+
+		linkPath := filepath.Join(linkDir, filepath.Base(targetPath))
+
+		expected := linkDir
+
+		actual, err := resolveSymlinkAncestor(linkPath)
+		if err != nil {
+			t.Errorf("expected err to be nil but was %s", err)
+		}
+
+		if actual != expected {
+			t.Errorf("expected result to be %s not %s", expected, actual)
+		}
+	})
+
+	t.Run("parent of path is a dead symlink", func(t *testing.T) {
+		testDir, targetPath := setupDirs(t)
+		defer os.RemoveAll(testDir)
+
+		targetDir := filepath.Dir(targetPath)
+
+		linkDir := filepath.Join(testDir, "foo")
+
+		if err := os.MkdirAll(linkDir, 0777); err != nil {
+			t.Fatal(err)
+		}
+
+		linkDir = filepath.Join(linkDir, "gaz")
+
+		if err := os.Symlink(targetDir, linkDir); err != nil {
+			t.Fatal(err)
+		}
+
+		if err := os.RemoveAll(targetDir); err != nil {
+			t.Fatal(err)
+		}
+
+		linkPath := filepath.Join(linkDir, filepath.Base(targetPath))
+
+		_, err := resolveSymlinkAncestor(linkPath)
+		if err == nil {
+			t.Error("expected err to not be nil")
+		}
+	})
+
+	t.Run("great grandparent of path is a symlink", func(t *testing.T) {
+		testDir, targetPath := setupDirs(t)
+		defer os.RemoveAll(testDir)
+
+		targetDir := filepath.Dir(targetPath)
+
+		linkDir := filepath.Join(testDir, "foo")
+
+		if err := os.Symlink(filepath.Dir(targetDir), linkDir); err != nil {
+			t.Fatal(err)
+		}
+
+		linkPath := filepath.Join(
+			linkDir,
+			filepath.Join(
+				filepath.Base(targetDir),
+				filepath.Base(targetPath),
+			),
+		)
+
+		expected := linkDir
+
+		actual, err := resolveSymlinkAncestor(linkPath)
+		if err != nil {
+			t.Errorf("expected err to be nil but was %s", err)
+		}
+
+		if actual != expected {
+			t.Errorf("expected result to be %s not %s", expected, actual)
+		}
+	})
+}