Add support for buildMetadata in the kustomize generator

Read the buildMetadata field from the Flux Kustomization spec
and pass it through to the generated kustomization.yaml. This
allows users to enable originAnnotations and transformerAnnotations
per Kustomization without modifying the source repository.

Ref: fluxcd/kustomize-controller#1579
Signed-off-by: Pierre-Gilles Mialon <pmialon@gmail.com>

Author: Pierre-Gilles Mialon

kustomize/kustomize_generator.go

@@ -56,6 +56,7 @@ const (
 	imagesField           = "images"
 	namePrefixField       = "namePrefix"
 	nameSuffixField       = "nameSuffix"
+	buildMetadataField    = "buildMetadata"
 )
 
 // Action is the action that was taken on the kustomization file
@@ -296,6 +297,15 @@ func (g *Generator) WriteFile(dirPath string, opts ...SavingOptions) (Action, er
 		}
 	}
 
+	buildMetadata, _, err := g.getNestedStringSlice(specField, buildMetadataField)
+	if err != nil {
+		errf := CleanDirectory(dirPath, action)
+		return action, fmt.Errorf("unable to get buildMetadata: %w", fmt.Errorf("%v %v", err, errf))
+	}
+	if len(buildMetadata) > 0 {
+		kus.BuildMetadata = buildMetadata
+	}
+
 	manifest, err := yaml.Marshal(kus)
 	if err != nil {
 		errf := CleanDirectory(dirPath, action)

kustomize/kustomize_generator_test.go

@@ -243,6 +243,81 @@ func Test_Components(t *testing.T) {
 	}
 }
 
+func TestGenerator_BuildMetadata(t *testing.T) {
+	g := NewWithT(t)
+	dataKS, err := os.ReadFile("./testdata/buildMetadata/ks.yaml")
+	g.Expect(err).NotTo(HaveOccurred())
+
+	ks, err := readYamlObjects(strings.NewReader(string(dataKS)))
+	g.Expect(err).NotTo(HaveOccurred())
+
+	tmpDir, err := testTempDir(t)
+	g.Expect(err).ToNot(HaveOccurred())
+	g.Expect(copy.Copy("testdata/buildMetadata", tmpDir)).To(Succeed())
+	_, err = kustomize.NewGenerator(tmpDir, ks[0]).WriteFile(tmpDir)
+	g.Expect(err).NotTo(HaveOccurred())
+
+	// Read the generated kustomization.yaml and verify buildMetadata is set
+	kfileYAML, err := os.ReadFile(filepath.Join(tmpDir, "kustomization.yaml"))
+	g.Expect(err).NotTo(HaveOccurred())
+
+	var kus kustypes.Kustomization
+	g.Expect(yaml.Unmarshal(kfileYAML, &kus)).To(Succeed())
+	g.Expect(kus.BuildMetadata).To(Equal([]string{"originAnnotations", "transformerAnnotations"}))
+
+	// Verify that the build succeeds with buildMetadata set
+	resMap, err := kustomize.SecureBuild(tmpDir, tmpDir, false)
+	g.Expect(err).NotTo(HaveOccurred())
+	g.Expect(resMap.Resources()).To(HaveLen(1))
+}
+
+func TestGenerator_BuildMetadata_EmptySpec(t *testing.T) {
+	g := NewWithT(t)
+
+	// Flux Kustomization with no buildMetadata should not override defaults
+	ks := unstructured.Unstructured{Object: map[string]any{}}
+
+	tmpDir, err := testTempDir(t)
+	g.Expect(err).ToNot(HaveOccurred())
+	g.Expect(copy.Copy("testdata/buildMetadata", tmpDir)).To(Succeed())
+	_, err = kustomize.NewGenerator(tmpDir, ks).WriteFile(tmpDir)
+	g.Expect(err).NotTo(HaveOccurred())
+
+	kfileYAML, err := os.ReadFile(filepath.Join(tmpDir, "kustomization.yaml"))
+	g.Expect(err).NotTo(HaveOccurred())
+
+	var kus kustypes.Kustomization
+	g.Expect(yaml.Unmarshal(kfileYAML, &kus)).To(Succeed())
+	// The kustomization.yaml has no .resources field (only configMapGenerator),
+	// so the fallback "originAnnotations" is set to avoid empty build errors
+	g.Expect(kus.BuildMetadata).To(Equal([]string{"originAnnotations"}))
+}
+
+func TestGenerator_BuildMetadata_NoResources(t *testing.T) {
+	g := NewWithT(t)
+
+	// Flux Kustomization with buildMetadata but no resources in the kustomization.yaml
+	// The spec buildMetadata should override the fallback "originAnnotations"
+	ks := unstructured.Unstructured{Object: map[string]any{}}
+	err := unstructured.SetNestedStringSlice(ks.Object,
+		[]string{"transformerAnnotations"}, "spec", "buildMetadata")
+	g.Expect(err).ToNot(HaveOccurred())
+
+	tmpDir, err := testTempDir(t)
+	g.Expect(err).ToNot(HaveOccurred())
+	g.Expect(copy.Copy("testdata/noResources", tmpDir)).To(Succeed())
+	_, err = kustomize.NewGenerator(tmpDir, ks).WriteFile(tmpDir)
+	g.Expect(err).NotTo(HaveOccurred())
+
+	kfileYAML, err := os.ReadFile(filepath.Join(tmpDir, "kustomization.yaml"))
+	g.Expect(err).NotTo(HaveOccurred())
+
+	var kus kustypes.Kustomization
+	g.Expect(yaml.Unmarshal(kfileYAML, &kus)).To(Succeed())
+	// User-specified buildMetadata should override the fallback
+	g.Expect(kus.BuildMetadata).To(Equal([]string{"transformerAnnotations"}))
+}
+
 func Test_IsLocalRelativePath(t *testing.T) {
 	tests := []struct {
 		path     string

kustomize/testdata/buildMetadata/ks.yaml

@@ -0,0 +1,16 @@
+---
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: test-buildmetadata
+  namespace: test-namespace
+spec:
+  buildMetadata:
+    - originAnnotations
+    - transformerAnnotations
+  interval: 4m0s
+  path: ./
+  prune: true
+  sourceRef:
+    kind: GitRepository
+    name: app

kustomize/testdata/buildMetadata/kustomization.yaml

@@ -0,0 +1,7 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+configMapGenerator:
+  - name: test-configmap
+    literals:
+      - foo=bar
+      - baz=qux