Perform deep merge for template values

cmd/kops/BUILD.bazel

@@ -139,6 +139,7 @@ go_test(
         "delete_confirm_test.go",
         "integration_test.go",
         "lifecycle_integration_test.go",
+        "toolbox_template_test.go",
     ],
     data = [
         "//channels:channeldata",  # keep

cmd/kops/toolbox_template.go

@@ -223,15 +223,42 @@ func newTemplateContext(files []string) (map[string]interface{}, error) {
 				return nil, fmt.Errorf("unable decode the configuration file: %s, error: %v", j, err)
 			}
 
-			for k, v := range ctx {
-				context[k] = v
-			}
+			context = mergeValues(context, ctx)
 		}
 	}
 
 	return context, nil
 }
 
+// Merges source and destination map, preferring values from the source map
+// Copied from the Helm (https://github.com/kubernetes/helm) project:
+// https://github.com/kubernetes/helm/blob/282984e75fd115a0765730efe09d8257c72fa56d/cmd/helm/install.go#L302
+func mergeValues(dest map[string]interface{}, src map[string]interface{}) map[string]interface{} {
+	for k, v := range src {
+		// If the key doesn't exist already, then just set the key to that value
+		if _, exists := dest[k]; !exists {
+			dest[k] = v
+			continue
+		}
+		nextMap, ok := v.(map[string]interface{})
+		// If it isn't another map, overwrite the value
+		if !ok {
+			dest[k] = v
+			continue
+		}
+		// Edge case: If the key exists in the destination, but isn't a map
+		destMap, isMap := dest[k].(map[string]interface{})
+		// If the source map has a map for this key, prefer it
+		if !isMap {
+			dest[k] = v
+			continue
+		}
+		// If we got to this point, it is a map in both, so merge them
+		dest[k] = mergeValues(destMap, nextMap)
+	}
+	return dest
+}
+
 // expandFiles is responsible for resolving any references to directories
 func expandFiles(path string) ([]string, error) {
 	// @check if the path is a directory, if not we can return straight away

cmd/kops/toolbox_template_test.go

@@ -0,0 +1,79 @@
+/*
+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 main
+
+import (
+	"reflect"
+	"testing"
+)
+
+// Copied from the Helm (https://github.com/kubernetes/helm) project:
+// https://github.com/kubernetes/helm/blob/282984e75fd115a0765730efe09d8257c72fa56d/cmd/helm/install_test.go#L230
+func TestMergeValues(t *testing.T) {
+	nestedMap := map[string]interface{}{
+		"foo": "bar",
+		"baz": map[string]string{
+			"cool": "stuff",
+		},
+	}
+	anotherNestedMap := map[string]interface{}{
+		"foo": "bar",
+		"baz": map[string]string{
+			"cool":    "things",
+			"awesome": "stuff",
+		},
+	}
+	flatMap := map[string]interface{}{
+		"foo": "bar",
+		"baz": "stuff",
+	}
+	anotherFlatMap := map[string]interface{}{
+		"testing": "fun",
+	}
+
+	testMap := mergeValues(flatMap, nestedMap)
+	equal := reflect.DeepEqual(testMap, nestedMap)
+	if !equal {
+		t.Errorf("Expected a nested map to overwrite a flat value. Expected: %v, got %v", nestedMap, testMap)
+	}
+
+	testMap = mergeValues(nestedMap, flatMap)
+	equal = reflect.DeepEqual(testMap, flatMap)
+	if !equal {
+		t.Errorf("Expected a flat value to overwrite a map. Expected: %v, got %v", flatMap, testMap)
+	}
+
+	testMap = mergeValues(nestedMap, anotherNestedMap)
+	equal = reflect.DeepEqual(testMap, anotherNestedMap)
+	if !equal {
+		t.Errorf("Expected a nested map to overwrite another nested map. Expected: %v, got %v", anotherNestedMap, testMap)
+	}
+
+	testMap = mergeValues(anotherFlatMap, anotherNestedMap)
+	expectedMap := map[string]interface{}{
+		"testing": "fun",
+		"foo":     "bar",
+		"baz": map[string]string{
+			"cool":    "things",
+			"awesome": "stuff",
+		},
+	}
+	equal = reflect.DeepEqual(testMap, expectedMap)
+	if !equal {
+		t.Errorf("Expected a map with different keys to merge properly with another map. Expected: %v, got %v", expectedMap, testMap)
+	}
+}