Emit unmodified change events for directories

When a file changes, emit events for the seen parent
directories to ensure that those parents are included
in change streams such as archives. The parents are
needed accurately recreate diff representation apart
from a parent (such as overlay and aufs graph drivers
in Docker).

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

fs/diff_test.go

@@ -44,6 +44,7 @@ func TestSimpleDiff(t *testing.T) {
 		fstest.Remove("/etc/unexpected"),
 	)
 	diff := []TestChange{
+		Unchanged("/etc"),
 		Modify("/etc/hosts"),
 		Modify("/etc/profile"),
 		Delete("/etc/unexpected"),
@@ -70,6 +71,7 @@ func TestDirectoryReplace(t *testing.T) {
 		fstest.CreateFile("/dir1/f2", []byte("Now file"), 0666),
 	)
 	diff := []TestChange{
+		Unchanged("/dir1"),
 		Add("/dir1/f11"),
 		Modify("/dir1/f2"),
 	}
@@ -132,10 +134,13 @@ func TestParentDirectoryPermission(t *testing.T) {
 		fstest.CreateFile("/dir3/f", []byte("irrelevant"), 0644),
 	)
 	diff := []TestChange{
+		Unchanged("/dir1"),
 		Add("/dir1/d"),
 		Add("/dir1/d/f"),
 		Add("/dir1/f"),
+		Unchanged("/dir2"),
 		Add("/dir2/f"),
+		Unchanged("/dir3"),
 		Add("/dir3/f"),
 	}
 
@@ -184,6 +189,56 @@ func TestUpdateWithSameTime(t *testing.T) {
 	}
 }
 
+func TestUnchangedParent(t *testing.T) {
+	skipDiffTestOnWindows(t)
+	l1 := fstest.Apply(
+		fstest.CreateDir("/dir1", 0755),
+		fstest.CreateDir("/dir3", 0755),
+		fstest.CreateDir("/dir3/a", 0755),
+		fstest.CreateDir("/dir3/a/e", 0755),
+		fstest.CreateDir("/dir3/z", 0755),
+	)
+	l2 := fstest.Apply(
+		fstest.CreateDir("/dir1/a", 0755),
+		fstest.CreateFile("/dir1/a/b", []byte("irrelevant"), 0644),
+		fstest.CreateDir("/dir1/a/e", 0755),
+		fstest.CreateFile("/dir1/a/e/f", []byte("irrelevant"), 0644),
+		fstest.CreateFile("/dir1/f", []byte("irrelevant"), 0644),
+		fstest.CreateDir("/dir2", 0755),
+		fstest.CreateFile("/dir2/f", []byte("irrelevant"), 0644),
+		fstest.CreateFile("/dir3/a/b", []byte("irrelevant"), 0644),
+		fstest.CreateDir("/dir3/a/c", 0755),
+		fstest.CreateDir("/dir3/a/e/i", 0755),
+		fstest.CreateFile("/dir3/a/e/i/f", []byte("irrelevant"), 0644),
+		fstest.CreateFile("/dir3/f", []byte("irrelevant"), 0644),
+		fstest.CreateFile("/dir3/z/f", []byte("irrelevant"), 0644),
+	)
+	diff := []TestChange{
+		Unchanged("/dir1"),
+		Add("/dir1/a"),
+		Add("/dir1/a/b"),
+		Add("/dir1/a/e"),
+		Add("/dir1/a/e/f"),
+		Add("/dir1/f"),
+		Add("/dir2"),
+		Add("/dir2/f"),
+		Unchanged("/dir3"),
+		Unchanged("/dir3/a"),
+		Add("/dir3/a/b"),
+		Add("/dir3/a/c"),
+		Unchanged("/dir3/a/e"),
+		Add("/dir3/a/e/i"),
+		Add("/dir3/a/e/i/f"),
+		Add("/dir3/f"),
+		Unchanged("/dir3/z"),
+		Add("/dir3/z/f"),
+	}
+
+	if err := testDiffWithBase(l1, l2, diff); err != nil {
+		t.Fatalf("Failed diff with base: %+v", err)
+	}
+}
+
 // buildkit#172
 func TestLchtimes(t *testing.T) {
 	skipDiffTestOnWindows(t)
@@ -347,7 +402,7 @@ func diffString(c1, c2 []TestChange) string {
 func changesString(c []TestChange) string {
 	strs := make([]string, len(c))
 	for i := range c {
-		strs[i] = fmt.Sprintf("\t%s\t%s", c[i].Kind, c[i].Path)
+		strs[i] = fmt.Sprintf("\t%-10s\t%s", c[i].Kind, c[i].Path)
 	}
 	return strings.Join(strs, "\n")
 }
@@ -372,3 +427,10 @@ func Modify(p string) TestChange {
 		Path: filepath.FromSlash(p),
 	}
 }
+
+func Unchanged(p string) TestChange {
+	return TestChange{
+		Kind: ChangeKindUnmodified,
+		Path: filepath.FromSlash(p),
+	}
+}