feat: add support for resource-policy: keep (#246) (#582)

The annotation `helm.sh/resource-policy: keep` instructs Helm to skip
deleting this resource when a Helm operation would result in its
deletion. As the resource is not actually deleted, exclude it from the
generated diff.

diff/diff.go

@@ -58,7 +58,9 @@ func Manifests(oldIndex, newIndex map[string]*manifest.MappingResult, options *O
 
 	for _, key := range removed {
 		oldContent := oldIndex[key]
-		doDiff(&report, key, oldContent, nil, options)
+		if oldContent.ResourcePolicy != "keep" {
+			doDiff(&report, key, oldContent, nil, options)
+		}
 	}
 
 	for _, key := range added {

diff/diff_test.go

@@ -259,6 +259,22 @@ spec:
 `,
 		}}
 
+	specReleaseKeep := map[string]*manifest.MappingResult{
+		"default, nginx, Deployment (apps)": {
+
+			Name: "default, nginx, Deployment (apps)",
+			Kind: "Deployment",
+			Content: `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: nginx
+annotations:
+  helm.sh/resource-policy: keep
+`,
+			ResourcePolicy: "keep",
+		}}
+
 	t.Run("OnChange", func(t *testing.T) {
 		var buf1 bytes.Buffer
 		diffOptions := Options{"diff", 10, false, true, []string{}, 0.0, []string{}}
@@ -438,6 +454,35 @@ spec:
 		require.Equal(t, ``, buf2.String())
 	})
 
+	t.Run("OnChangeRemoved", func(t *testing.T) {
+		var buf1 bytes.Buffer
+		diffOptions := Options{"diff", 10, false, true, []string{}, 0.5, []string{}}
+
+		if changesSeen := Manifests(specRelease, nil, &diffOptions, &buf1); !changesSeen {
+			t.Error("Unexpected return value from Manifests: Expected the return value to be `true` to indicate that it has seen any change(s), but was `false`")
+		}
+
+		require.Equal(t, `default, nginx, Deployment (apps) has been removed:
+
+- apiVersion: apps/v1
+- kind: Deployment
+- metadata:
+-   name: nginx
+- `+`
+`, buf1.String())
+	})
+
+	t.Run("OnChangeRemovedWithResourcePolicyKeep", func(t *testing.T) {
+		var buf2 bytes.Buffer
+		diffOptions := Options{"diff", 10, false, true, []string{}, 0.0, []string{}}
+
+		if changesSeen := Manifests(specReleaseKeep, nil, &diffOptions, &buf2); changesSeen {
+			t.Error("Unexpected return value from Manifests: Expected the return value to be `false` to indicate that it has NOT seen any change(s), but was `true`")
+		}
+
+		require.Equal(t, ``, buf2.String())
+	})
+
 	t.Run("OnChangeSimple", func(t *testing.T) {
 		var buf1 bytes.Buffer
 		diffOptions := Options{"simple", 10, false, true, []string{}, 0.0, []string{}}

manifest/parse.go

@@ -11,16 +11,18 @@ import (
 )
 
 const (
-	hookAnnotation = "helm.sh/hook"
+	hookAnnotation           = "helm.sh/hook"
+	resourcePolicyAnnotation = "helm.sh/resource-policy"
 )
 
 var yamlSeparator = []byte("\n---\n")
 
 // MappingResult to store result of diff
 type MappingResult struct {
-	Name    string
-	Kind    string
-	Content string
+	Name           string
+	Kind           string
+	Content        string
+	ResourcePolicy string
 }
 
 type metadata struct {
@@ -169,9 +171,10 @@ func parseContent(content string, defaultNamespace string, normalizeManifests bo
 	name := parsedMetadata.String()
 	return []*MappingResult{
 		{
-			Name:    name,
-			Kind:    parsedMetadata.Kind,
-			Content: content,
+			Name:           name,
+			Kind:           parsedMetadata.Kind,
+			Content:        content,
+			ResourcePolicy: parsedMetadata.Metadata.Annotations[resourcePolicyAnnotation],
 		},
 	}, nil
 }