Address comments: add unit tests, defaulting and update comment

pkg/types/defaulting.go

@@ -0,0 +1,27 @@
+/*
+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 types
+
+import (
+	corev1 "k8s.io/api/core/v1"
+)
+
+func (v *Var) Defaulting() {
+	if (corev1.ObjectFieldSelector{}) == v.FieldRef {
+		v.FieldRef = corev1.ObjectFieldSelector{FieldPath: "metadata.name"}
+	}
+}

pkg/types/kustomization.go

@@ -137,16 +137,22 @@ type DataSources struct {
 	EnvSource string `json:"env,omitempty" yaml:"env,omitempty"`
 }
 
-// Var represents a variable whose value will be source'd from a Kubernetes object
-// and will be substituted at runtime.
+// Var represents a variable whose value will be sourced
+// from a field in a Kubernetes object.
 type Var struct {
 	// Value of identifier name e.g. FOO used in container args, annotations
 	// Appears in pod template as $(FOO)
 	Name string `json:"name" yaml:"name"`
 
-	// ObjRef refers to a Kubernetes Resource
+	// ObjRef must refer to a Kubernetes resource under the
+	// purview of this kustomization. ObjRef should use the
+	// raw name of the object (the name specified in its YAML,
+	// before addition of a namePrefix).
 	ObjRef corev1.ObjectReference `json:"objref" yaml:"objref"`
 
-	// FieldRef refers to the fieldpath to extract value from a Kubernetes Object
-	FieldRef corev1.ObjectFieldSelector `json:"fieldref" yaml:"objref"`
+	// FieldRef refers to the field of the object referred to by
+	// ObjRef whose value will be extracted for use in
+	// replacing $(FOO).
+	// If unspecified, this defaults to fieldpath: metadata.name
+	FieldRef corev1.ObjectFieldSelector `json:"fieldref,omitempty" yaml:"objref,omitempty"`
 }