Address comments: add unit tests, defaulting and update comment

pkg/app/application.go

@@ -347,7 +347,10 @@ func (a *applicationImpl) Vars() ([]types.Var, error) {
 		}
 		vars = append(vars, subAppVars...)
 	}
-	vars = append(vars, a.kustomization.Vars...)
+	for _, v := range a.kustomization.Vars {
+		v.Defaulting()
+		vars = append(vars, v)
+	}
 	if len(errs.Get()) > 0 {
 		return nil, errs
 	}

pkg/app/var.go

@@ -1,3 +1,19 @@
+/*
+Copyright 2018 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 app
 
 import (

pkg/app/var_test.go

@@ -0,0 +1,51 @@
+/*
+Copyright 2018 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 app
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestGetFieldAsString(t *testing.T) {
+	m := map[string]interface{}{
+		"Kind": "Service",
+		"metadata": map[string]interface{}{
+			"labels": map[string]string{
+				"app": "application-name",
+			},
+			"name": "service-name",
+		},
+	}
+	p := []string{"Kind"}
+	s, _ := getFieldAsString(m, p)
+	if s != "Service" {
+		t.Errorf("Expected to get Service, but actually got %s", s)
+	}
+
+	p = []string{"metadata", "name"}
+	s, _ = getFieldAsString(m, p)
+	if s != "service-name" {
+		t.Errorf("Expected to get service-name, but actually got %s", s)
+	}
+
+	p = []string{"metadata", "non-existing-field"}
+	s, err := getFieldAsString(m, p)
+	if !strings.HasSuffix(err.Error(), "field at given fieldpath does not exist") {
+		t.Errorf("Unexpected failure due to incorrect error message %s", err.Error())
+	}
+}

pkg/commands/testdata/testcase-variable-ref/test.yaml

@@ -1,4 +1,4 @@
-description: varialbe reference and substitution
+description: variable reference and substitution
 args: []
 filename: testdata/testcase-variable-ref/in/overlay/
 expectedStdout: testdata/testcase-variable-ref/expected.yaml

pkg/transformers/refvars.go

@@ -72,7 +72,6 @@ func (rv *refvarTransformer) Transform(resources resmap.ResMap) error {
 				default:
 					return "", fmt.Errorf("invalid type encountered %T", vt)
 				}
-				return "", fmt.Errorf("invalid type encountered")
 			})
 			if err != nil {
 				return err

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"`
 }