Add strategic merge patch filter based on kyaml libraries

api/filters/patchstrategicmerge/doc.go

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+// Copyright 2020 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+// Package patchstrategicmerge contains a kio.Filter implementation of the
+// kustomize strategic merge patch transformer.
+package patchstrategicmerge

api/filters/patchstrategicmerge/example_test.go

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+// Copyright 2020 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package patchstrategicmerge
+
+import (
+	"bytes"
+	"log"
+	"os"
+
+	"sigs.k8s.io/kustomize/kyaml/kio"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+)
+
+func ExampleFilter() {
+	err := kio.Pipeline{
+		Inputs: []kio.Reader{&kio.ByteReader{Reader: bytes.NewBufferString(`
+apiVersion: example.com/v1
+kind: Foo
+metadata:
+  name: instance
+spec:
+  replicas: 3
+`)}},
+		Filters: []kio.Filter{Filter{
+			Patch: yaml.MustParse(`
+spec:
+  template:
+    containers:
+    - image: nginx
+`),
+		}},
+		Outputs: []kio.Writer{kio.ByteWriter{Writer: os.Stdout}},
+	}.Execute()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Output:
+	// apiVersion: example.com/v1
+	// kind: Foo
+	// metadata:
+	//   name: instance
+	// spec:
+	//   replicas: 3
+	//   template:
+	//     containers:
+	//     - image: nginx
+}

api/filters/patchstrategicmerge/patchstrategicmerge.go

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+package patchstrategicmerge
+
+import (
+	"sigs.k8s.io/kustomize/kyaml/kio"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+	"sigs.k8s.io/kustomize/kyaml/yaml/merge2"
+)
+
+type Filter struct {
+	Patch *yaml.RNode
+}
+
+var _ kio.Filter = Filter{}
+
+func (pf Filter) Filter(nodes []*yaml.RNode) ([]*yaml.RNode, error) {
+	return kio.FilterAll(yaml.FilterFunc(pf.run)).Filter(nodes)
+}
+
+func (pf Filter) run(node *yaml.RNode) (*yaml.RNode, error) {
+	return merge2.Merge(pf.Patch, node)
+}

api/filters/patchstrategicmerge/patchstrategicmerge_test.go

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+package patchstrategicmerge
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	filtertest "sigs.k8s.io/kustomize/api/testutils/filtertest"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+)
+
+func TestFilter(t *testing.T) {
+	testCases := map[string]struct {
+		input    string
+		patch    *yaml.RNode
+		expected string
+	}{
+		"simple patch": {
+			input: `
+apiVersion: apps/v1
+metadata:
+  name: myDeploy
+kind: Deployment
+`,
+			patch: yaml.MustParse(`
+metadata:
+  name: yourDeploy
+`),
+			expected: `
+apiVersion: apps/v1
+metadata:
+  name: yourDeploy
+kind: Deployment
+`,
+		},
+		"nested patch": {
+			input: `
+apiVersion: apps/v1
+metadata:
+  name: myDeploy
+kind: Deployment
+spec:
+  containers:
+  - name: nginx
+    args:
+    - abc
+`,
+			patch: yaml.MustParse(`
+spec:
+  containers:
+  - name: nginx
+    args:
+    - def
+`),
+			expected: `
+apiVersion: apps/v1
+metadata:
+  name: myDeploy
+kind: Deployment
+spec:
+  containers:
+  - name: nginx
+    args:
+    - def
+`,
+		},
+	}
+
+	for tn, tc := range testCases {
+		t.Run(tn, func(t *testing.T) {
+			f := Filter{
+				Patch: tc.patch,
+			}
+			if !assert.Equal(t,
+				strings.TrimSpace(tc.expected),
+				strings.TrimSpace(
+					filtertest.RunFilter(t, tc.input, f))) {
+				t.FailNow()
+			}
+		})
+	}
+}