Beginning of rewrite apply merge-logic using visitor pattern.

Major changes:
- Don't generate a patch, instead generate the merged object so it can be used with PUT
- Separate tree parsing logic to collate items in a list from the delete / merge / replace / add logic when merging
- Use openapi for merge strategy metadata so it works with extensions and version skew
- Support multi-field mergekeys when merging lists
- Support replace strategy for maps
- Reduce complexity of generating order when merging lists - keep the locally defined order and append remote only-items

Continue to support:
- Explicitly setting fields to null
- Merging lists of primitives
- Don't randomize ordering when merging lists

TODO:
- Retain keys
- Conflict detection

pkg/kubectl/apply/parse/visitor.go

@@ -0,0 +1,79 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package parse
+
+import (
+	"k8s.io/kubernetes/pkg/kubectl/apply"
+	"k8s.io/kubernetes/pkg/kubectl/cmd/util/openapi"
+)
+
+// ItemVisitor provides an interface for Items to Accept and call
+// the Visit function that corresponds to its actual type.
+type ItemVisitor interface {
+	// CreatePrimitiveElement builds an Element for a primitiveItem
+	CreatePrimitiveElement(*primitiveItem) (apply.Element, error)
+
+	// CreateListElement builds an Element for a listItem
+	CreateListElement(*listItem) (apply.Element, error)
+
+	// CreateMapElement builds an Element for a mapItem
+	CreateMapElement(*mapItem) (apply.Element, error)
+
+	// CreateTypeElement builds an Element for a typeItem
+	CreateTypeElement(*typeItem) (apply.Element, error)
+}
+
+// ElementBuildingVisitor creates an Elements from Items
+// An Element combines the values from the Item with the field metadata.
+type ElementBuildingVisitor struct {
+	resources openapi.Resources
+}
+
+// CreatePrimitiveElement creates a primitiveElement
+func (v ElementBuildingVisitor) CreatePrimitiveElement(item *primitiveItem) (apply.Element, error) {
+	return v.primitiveElement(item)
+}
+
+// CreateListElement creates a ListElement
+func (v ElementBuildingVisitor) CreateListElement(item *listItem) (apply.Element, error) {
+	meta, err := getFieldMeta(item.GetMeta(), item.Name)
+	if err != nil {
+		return nil, err
+	}
+	if meta.GetFieldMergeType() == "merge" {
+		return v.mergeListElement(meta, item)
+	}
+	return v.replaceListElement(meta, item)
+}
+
+// CreateMapElement creates a mapElement
+func (v ElementBuildingVisitor) CreateMapElement(item *mapItem) (apply.Element, error) {
+	meta, err := getFieldMeta(item.GetMeta(), item.Name)
+	if err != nil {
+		return nil, err
+	}
+	return v.mapElement(meta, item)
+}
+
+// CreateTypeElement creates a typeElement
+func (v ElementBuildingVisitor) CreateTypeElement(item *typeItem) (apply.Element, error) {
+	meta, err := getFieldMeta(item.GetMeta(), item.Name)
+	if err != nil {
+		return nil, err
+	}
+	return v.typeElement(meta, item)
+}