implement TrackableFilter with labels

This updates the labels filter to implement the TrackableFilter
interface by reusing the TrackableSetter abstraction provided by
filtersutil.

This is done to provide a generic and consistent experience across the
filters

api/filters/labels/labels.go

@@ -21,22 +21,15 @@ type Filter struct {
 	// FsSlice identifies the label fields.
 	FsSlice types.FsSlice
 
-	// SetEntryCallback is invoked each time a label is applied
-	// Example use cases:
-	//   - Tracking all paths where labels have been applied
-	SetEntryCallback func(key, value, tag string, node *yaml.RNode)
+	setter filtersutil.TrackableSetter
 }
 
 var _ kio.Filter = Filter{}
+var _ kio.TrackableFilter = &Filter{}
 
-func (f Filter) setEntry(key, value, tag string) filtersutil.SetFn {
-	baseSetEntryFunc := filtersutil.SetEntry(key, value, tag)
-	return func(node *yaml.RNode) error {
-		if f.SetEntryCallback != nil {
-			f.SetEntryCallback(key, value, tag, node)
-		}
-		return baseSetEntryFunc(node)
-	}
+// WithMutationTracker registers a callback which will be invoked each time a field is mutated
+func (f *Filter) WithMutationTracker(callback func(key, value, tag string, node *yaml.RNode)) {
+	f.setter.WithMutationTracker(callback)
 }
 
 func (f Filter) Filter(nodes []*yaml.RNode) ([]*yaml.RNode, error) {
@@ -46,7 +39,7 @@ func (f Filter) Filter(nodes []*yaml.RNode) ([]*yaml.RNode, error) {
 			for _, k := range keys {
 				if err := node.PipeE(fsslice.Filter{
 					FsSlice: f.FsSlice,
-					SetValue: f.setEntry(
+					SetValue: f.setter.SetEntry(
 						k, f.Labels[k], yaml.NodeTagString),
 					CreateKind: yaml.MappingNode, // Labels are MappingNodes.
 					CreateTag:  yaml.NodeTagMap,

api/filters/labels/labels_test.go

@@ -37,6 +37,7 @@ func TestLabels_Filter(t *testing.T) {
 		input                string
 		expectedOutput       string
 		filter               Filter
+		setEntryCallback     func(key, value, tag string, node *yaml.RNode)
 		expectedSetEntryArgs []setEntryArg
 	}{
 		"add": {
@@ -456,8 +457,8 @@ a:
 						CreateIfNotPresent: true,
 					},
 				},
-				SetEntryCallback: setEntryCallbackStub,
 			},
+			setEntryCallback: setEntryCallbackStub,
 			expectedSetEntryArgs: []setEntryArg{
 				{
 					Key:      "mage",
@@ -478,6 +479,7 @@ a:
 	for tn, tc := range testCases {
 		setEntryArgs = nil
 		t.Run(tn, func(t *testing.T) {
+			tc.filter.WithMutationTracker(tc.setEntryCallback)
 			if !assert.Equal(t,
 				strings.TrimSpace(tc.expectedOutput),
 				strings.TrimSpace(filtertest_test.RunFilter(t, tc.input, tc.filter))) {