Retain element ordering when merge resources

kyaml/kio/filters/merge.go

@@ -41,6 +41,8 @@ func (c MergeFilter) Filter(input []*yaml.RNode) ([]*yaml.RNode, error) {
 
 	// index the Resources by G/V/K/NS/N
 	index := map[mergeKey][]*yaml.RNode{}
+	// retain the original ordering
+	var order []mergeKey
 	for i := range input {
 		meta, err := input[i].GetMeta()
 		if err != nil {
@@ -52,13 +54,16 @@ func (c MergeFilter) Filter(input []*yaml.RNode) ([]*yaml.RNode, error) {
 			namespace:  meta.Namespace,
 			name:       meta.Name,
 		}
+		if _, found := index[key]; !found {
+			order = append(order, key)
+		}
 		index[key] = append(index[key], input[i])
 	}
 
 	// merge each of the G/V/K/NS/N lists
 	var output []*yaml.RNode
 	var err error
-	for k := range index {
+	for _, k := range order {
 		var merged *yaml.RNode
 		resources := index[k]
 		for i := range resources {

kyaml/kio/filters/merge_test.go

@@ -0,0 +1,115 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package filters_test
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"sigs.k8s.io/kustomize/kyaml/kio"
+	"sigs.k8s.io/kustomize/kyaml/kio/filters"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+)
+
+// TestMerge_Merge_order tests that the original order of elements
+// retained after merge
+func TestMerge_Merge_order(t *testing.T) {
+	r1, err := yaml.Parse(`
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: foo-1
+  namespace: bar-1
+spec:
+  template:
+    spec: {}
+`)
+	if !assert.NoError(t, err) {
+		t.FailNow()
+	}
+
+	r2, err := yaml.Parse(`
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: foo-2
+  namespace: bar-2
+spec:
+  template:
+    spec: {}
+`)
+	if !assert.NoError(t, err) {
+		t.FailNow()
+	}
+
+	var b bytes.Buffer
+	err = kio.Pipeline{
+		Inputs:  []kio.Reader{&kio.PackageBuffer{Nodes: []*yaml.RNode{r1, r2}}},
+		Filters: []kio.Filter{filters.MatchFilter{}},
+		Outputs: []kio.Writer{&kio.ByteWriter{Writer: &b}},
+	}.Execute()
+	if !assert.NoError(t, err) {
+		t.FailNow()
+	}
+
+	expected := strings.TrimSpace(`
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: foo-1
+  namespace: bar-1
+spec:
+  template:
+    spec: {}
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: foo-2
+  namespace: bar-2
+spec:
+  template:
+    spec: {}
+`)
+
+	if !assert.Equal(t, expected, strings.TrimSpace(b.String())) {
+		t.FailNow()
+	}
+
+	b.Reset()
+	err = kio.Pipeline{
+		Inputs:  []kio.Reader{&kio.PackageBuffer{Nodes: []*yaml.RNode{r2, r1}}},
+		Filters: []kio.Filter{filters.MatchFilter{}},
+		Outputs: []kio.Writer{&kio.ByteWriter{Writer: &b}},
+	}.Execute()
+	if !assert.NoError(t, err) {
+		t.FailNow()
+	}
+
+	expected = strings.TrimSpace(`
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: foo-2
+  namespace: bar-2
+spec:
+  template:
+    spec: {}
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: foo-1
+  namespace: bar-1
+spec:
+  template:
+    spec: {}
+`)
+
+	if !assert.Equal(t, expected, strings.TrimSpace(b.String())) {
+		t.FailNow()
+	}
+}