feat: implement TrackableFilter for replicacount

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

api/filters/replicacount/replicacount.go

@@ -14,9 +14,17 @@ import (
 type Filter struct {
 	Replica   types.Replica   `json:"replica,omitempty" yaml:"replica,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 (rc *Filter) WithMutationTracker(callback func(key, value, tag string, node *yaml.RNode)) {
+	rc.trackableSetter.WithMutationTracker(callback)
+}
 
 func (rc Filter) Filter(nodes []*yaml.RNode) ([]*yaml.RNode, error) {
 	return kio.FilterAll(yaml.FilterFunc(rc.run)).Filter(nodes)
@@ -33,5 +41,5 @@ func (rc Filter) run(node *yaml.RNode) (*yaml.RNode, error) {
 }
 
 func (rc Filter) set(node *yaml.RNode) error {
-	return filtersutil.SetScalar(strconv.FormatInt(rc.Replica.Count, 10))(node)
+	return rc.trackableSetter.SetScalar(strconv.FormatInt(rc.Replica.Count, 10))(node)
 }

api/filters/replicacount/replicacount_test.go

@@ -7,14 +7,17 @@ import (
 	"github.com/stretchr/testify/assert"
 	filtertest_test "sigs.k8s.io/kustomize/api/testutils/filtertest"
 	"sigs.k8s.io/kustomize/api/types"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
 )
 
 func TestFilter(t *testing.T) {
-
+	mutationTrackerStub := filtertest_test.MutationTrackerStub{}
 	testCases := map[string]struct {
-		input    string
-		expected string
-		filter   Filter
+		input                string
+		expected             string
+		filter               Filter
+		mutationTracker      func(key, value, tag string, node *yaml.RNode)
+		expectedSetValueArgs []filtertest_test.SetValueArg
 	}{
 		"update field": {
 			input: `
@@ -161,9 +164,43 @@ spec:
 				FieldSpec: types.FieldSpec{Path: "spec/template/replicas"},
 			},
 		},
+		"mutation tracker": {
+			input: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: dep
+spec:
+  replicas: 5
+`,
+			expected: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: dep
+spec:
+  replicas: 42
+`,
+			filter: Filter{
+				Replica: types.Replica{
+					Name:  "dep",
+					Count: 42,
+				},
+				FieldSpec: types.FieldSpec{Path: "spec/replicas"},
+			},
+			mutationTracker: mutationTrackerStub.MutationTracker,
+			expectedSetValueArgs: []filtertest_test.SetValueArg{
+				{
+					Value:    "42",
+					NodePath: []string{"spec", "replicas"},
+				},
+			},
+		},
 	}
 
 	for tn, tc := range testCases {
+		mutationTrackerStub.Reset()
+		tc.filter.WithMutationTracker(tc.mutationTracker)
 		t.Run(tn, func(t *testing.T) {
 			if !assert.Equal(t,
 				strings.TrimSpace(tc.expected),
@@ -171,6 +208,7 @@ spec:
 					filtertest_test.RunFilter(t, tc.input, tc.filter))) {
 				t.FailNow()
 			}
+			assert.Equal(t, tc.expectedSetValueArgs, mutationTrackerStub.SetValueArgs())
 		})
 	}
 }