sync: add tests to check dir modtimes are kept when syncing

This adds tests to check dir modtimes are updated from source
when syncing even if they've changed in the destination.
This should work both with and without --copy-empty-src-dirs.

fs/sync/sync_test.go

@@ -2762,6 +2762,81 @@ func TestSyncConcurrentTruncate(t *testing.T) {
 	testSyncConcurrent(t, "truncate")
 }
 
+// Test that sync replaces dir modtimes in dst if they've changed
+func testSyncReplaceDirModTime(t *testing.T, copyEmptySrcDirs bool) {
+	accounting.GlobalStats().ResetCounters()
+	ctx, _ := fs.AddConfig(context.Background())
+	r := fstest.NewRun(t)
+
+	file1 := r.WriteFile("file1", "file1", t2)
+	file2 := r.WriteFile("test_dir1/file2", "file2", t2)
+	file3 := r.WriteFile("test_dir2/sub_dir/file3", "file3", t2)
+	r.CheckLocalItems(t, file1, file2, file3)
+
+	_, err := operations.MkdirModTime(ctx, r.Flocal, "empty_dir", t2)
+	require.NoError(t, err)
+
+	// A directory that's empty on both src and dst
+	_, err = operations.MkdirModTime(ctx, r.Flocal, "empty_on_remote", t2)
+	require.NoError(t, err)
+	_, err = operations.MkdirModTime(ctx, r.Fremote, "empty_on_remote", t2)
+	require.NoError(t, err)
+
+	// set logging
+	// (this checks log output as DirModtime operations do not yet have stats, and r.CheckDirectoryModTimes also does not tell us what actions were taken)
+	oldLogLevel := fs.GetConfig(context.Background()).LogLevel
+	defer func() { fs.GetConfig(context.Background()).LogLevel = oldLogLevel }() // reset to old val after test
+	// need to do this as fs.Infof only respects the globalConfig
+	fs.GetConfig(context.Background()).LogLevel = fs.LogLevelInfo
+
+	// First run
+	accounting.GlobalStats().ResetCounters()
+	ctx = predictDstFromLogger(ctx)
+	output := bilib.CaptureOutput(func() {
+		err := CopyDir(ctx, r.Fremote, r.Flocal, copyEmptySrcDirs)
+		require.NoError(t, err)
+	})
+	require.NotNil(t, output)
+	testLoggerVsLsf(ctx, r.Fremote, operations.GetLoggerOpt(ctx).JSON, t)
+
+	// Save all dirs
+	dirs := []string{"test_dir1", "test_dir2", "test_dir2/sub_dir", "empty_on_remote"}
+	if copyEmptySrcDirs {
+		dirs = append(dirs, "empty_dir")
+	}
+
+	// Change dir modtimes
+	for _, dir := range dirs {
+		_, err := operations.SetDirModTime(ctx, r.Flocal, nil, dir, t1)
+		if err != nil && !errors.Is(err, fs.ErrorNotImplemented) {
+			require.NoError(t, err)
+		}
+	}
+
+	// Run again
+	accounting.GlobalStats().ResetCounters()
+	ctx = predictDstFromLogger(ctx)
+	output = bilib.CaptureOutput(func() {
+		err := CopyDir(ctx, r.Fremote, r.Flocal, copyEmptySrcDirs)
+		require.NoError(t, err)
+	})
+	require.NotNil(t, output)
+	testLoggerVsLsf(ctx, r.Fremote, operations.GetLoggerOpt(ctx).JSON, t)
+	r.CheckLocalItems(t, file1, file2, file3)
+	r.CheckRemoteItems(t, file1, file2, file3)
+
+	// Check that the modtimes of the directories are as expected
+	r.CheckDirectoryModTimes(t, dirs...)
+}
+
+func TestSyncReplaceDirModTime(t *testing.T) {
+	testSyncReplaceDirModTime(t, false)
+}
+
+func TestSyncReplaceDirModTimeWithEmptyDirs(t *testing.T) {
+	testSyncReplaceDirModTime(t, true)
+}
+
 // Tests that nothing is transferred when src and dst already match
 // Run the same sync twice, ensure no action is taken the second time
 func testNothingToTransfer(t *testing.T, copyEmptySrcDirs bool) {