feat: implement TrackableFilter for prefix

This change updates the prefix filter to implement the TrackableFilter
interface. This provides the functionality for the user to track which
fields were updated by the prefix filter.

api/filters/prefix/prefix.go

@@ -18,9 +18,17 @@ type Filter struct {
 	Prefix string `json:"prefix,omitempty" yaml:"prefix,omitempty"`
 
 	FieldSpec types.FieldSpec `json:"fieldSpec,omitempty" yaml:"fieldSpec,omitempty"`
+
+	trackableSetter filtersutil.TrackableSetter
 }
 
 var _ kio.Filter = Filter{}
+var _ kio.TrackableFilter = &Filter{}
+
+// 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.trackableSetter.WithMutationTracker(callback)
+}
 
 func (f Filter) Filter(nodes []*yaml.RNode) ([]*yaml.RNode, error) {
 	return kio.FilterAll(yaml.FilterFunc(f.run)).Filter(nodes)
@@ -37,6 +45,6 @@ func (f Filter) run(node *yaml.RNode) (*yaml.RNode, error) {
 }
 
 func (f Filter) evaluateField(node *yaml.RNode) error {
-	return filtersutil.SetScalar(fmt.Sprintf(
+	return f.trackableSetter.SetScalar(fmt.Sprintf(
 		"%s%s", f.Prefix, node.YNode().Value))(node)
 }

api/filters/prefix/prefix_test.go

@@ -11,8 +11,11 @@ import (
 	"sigs.k8s.io/kustomize/api/filters/prefix"
 	filtertest_test "sigs.k8s.io/kustomize/api/testutils/filtertest"
 	"sigs.k8s.io/kustomize/api/types"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
 )
 
+var mutationTrackerStub = filtertest_test.MutationTrackerStub{}
+
 var tests = map[string]TestCase{
 	"prefix": {
 		input: `
@@ -83,17 +86,61 @@ a:
 			FieldSpec: types.FieldSpec{Path: "a/b/c"},
 		},
 	},
+
+	"mutation tracker": {
+		input: `
+apiVersion: example.com/v1
+kind: Foo
+metadata:
+  name: instance
+---
+apiVersion: example.com/v1
+kind: Bar
+metadata:
+  name: instance
+`,
+		expected: `
+apiVersion: example.com/v1
+kind: Foo
+metadata:
+  name: foo-instance
+---
+apiVersion: example.com/v1
+kind: Bar
+metadata:
+  name: foo-instance
+`,
+		filter: prefix.Filter{
+			Prefix:    "foo-",
+			FieldSpec: types.FieldSpec{Path: "metadata/name"},
+		},
+		mutationTracker: mutationTrackerStub.MutationTracker,
+		expectedSetValueArgs: []filtertest_test.SetValueArg{
+			{
+				Value:    "foo-instance",
+				NodePath: []string{"metadata", "name"},
+			},
+			{
+				Value:    "foo-instance",
+				NodePath: []string{"metadata", "name"},
+			},
+		},
+	},
 }
 
 type TestCase struct {
-	input    string
-	expected string
-	filter   prefix.Filter
+	input                string
+	expected             string
+	filter               prefix.Filter
+	mutationTracker      func(key, value, tag string, node *yaml.RNode)
+	expectedSetValueArgs []filtertest_test.SetValueArg
 }
 
 func TestFilter(t *testing.T) {
 	for name := range tests {
+		mutationTrackerStub.Reset()
 		test := tests[name]
+		test.filter.WithMutationTracker(test.mutationTracker)
 		t.Run(name, func(t *testing.T) {
 			if !assert.Equal(t,
 				strings.TrimSpace(test.expected),
@@ -101,6 +148,7 @@ func TestFilter(t *testing.T) {
 					filtertest_test.RunFilter(t, test.input, test.filter))) {
 				t.FailNow()
 			}
+			assert.Equal(t, test.expectedSetValueArgs, mutationTrackerStub.SetValueArgs())
 		})
 	}
 }