refactor the strategic merge patch transformer toward moving it to a plugin (#1340)

pkg/resmap/factory.go

@@ -14,11 +14,12 @@ import (
 // Factory makes instances of ResMap.
 type Factory struct {
 	resF *resource.Factory
+	tf   PatchFactory
 }
 
 // NewFactory returns a new resmap.Factory.
-func NewFactory(rf *resource.Factory) *Factory {
-	return &Factory{resF: rf}
+func NewFactory(rf *resource.Factory, tf PatchFactory) *Factory {
+	return &Factory{resF: rf, tf: tf}
 }
 
 // RF returns a resource.Factory.
@@ -118,6 +119,11 @@ func (rmF *Factory) FromSecretArgs(
 	return rmF.FromResource(res), nil
 }
 
+func (rmF *Factory) MergePatches(patches []*resource.Resource) (
+	ResMap, error) {
+	return rmF.tf.MergePatches(patches, rmF.resF)
+}
+
 func newResMapFromResourceSlice(resources []*resource.Resource) (ResMap, error) {
 	result := New()
 	for _, res := range resources {

pkg/resmap/patchfactory.go

@@ -0,0 +1,15 @@
+/// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+// Package patch holds miscellaneous interfaces used by kustomize.
+package resmap
+
+import (
+	"sigs.k8s.io/kustomize/v3/pkg/resource"
+)
+
+// PatchFactory makes transformers that require k8sdeps.
+type PatchFactory interface {
+	MergePatches(patches []*resource.Resource,
+		rf *resource.Factory) (ResMap, error)
+}

pkg/resmap/resmap_test.go

@@ -19,7 +19,7 @@ import (
 
 var rf = resource.NewFactory(
 	kunstruct.NewKunstructuredFactoryImpl())
-var rmF = NewFactory(rf)
+var rmF = NewFactory(rf, nil)
 
 func doAppend(t *testing.T, w ResMap, r *resource.Resource) {
 	err := w.Append(r)