google_artifact_registry_repository: Fix perma-diff in maven_config (#12190)

Author: Subserial

mmv1/products/artifactregistry/Repository.yaml

@@ -300,6 +300,7 @@ properties:
       Provides additional configuration details for repositories of the maven
       format type.
     allow_empty_object: true
+    diff_suppress_func: 'emptyMavenConfigDiffSuppress'
     properties:
       # Maven properties.
       - name: 'allowSnapshotOverwrites'

mmv1/templates/terraform/constants/artifact_registry_repository.go.tmpl

@@ -95,3 +95,22 @@ func mapHashID(v any) int {
 	obj := v.(map[string]any)
 	return schema.HashString(obj["id"])
 }
+
+func isDefaultEnum(val any) bool {
+  s, ok := val.(string)
+  if !ok {
+    return false
+  }
+  return s == "" || strings.HasSuffix(s, "_UNSPECIFIED")
+}
+
+// emptyMavenConfigDiffSuppress generates a config from defaults if it or any
+// properties are unset. Missing, empty and default configs are all equivalent.
+func emptyMavenConfigDiffSuppress(k, old, new string, d *schema.ResourceData) bool {
+  oSnap, nSnap := d.GetChange("maven_config.0.allow_snapshot_overwrites")
+  if oSnap.(bool) != nSnap.(bool) {
+    return false
+  }
+  oPolicy, nPolicy := d.GetChange("maven_config.0.version_policy")
+  return isDefaultEnum(oPolicy) && isDefaultEnum(nPolicy)
+}

mmv1/third_party/terraform/services/artifactregistry/resource_artifact_registry_repository_test.go.tmpl

@@ -84,6 +84,38 @@ func TestAccArtifactRegistryRepository_createMvnRelease(t *testing.T) {
 	})
 }
 
+func TestAccArtifactRegistryRepository_updateEmptyMvn(t *testing.T) {
+	t.Parallel()
+
+	repositoryID := fmt.Sprintf("tf-test-%d", acctest.RandInt(t))
+
+	acctest.VcrTest(t, resource.TestCase{
+		PreCheck:                 func() { acctest.AccTestPreCheck(t) },
+		ProtoV5ProviderFactories: acctest.ProtoV5ProviderFactories(t),
+		CheckDestroy:             testAccCheckArtifactRegistryRepositoryDestroyProducer(t),
+		Steps: []resource.TestStep{
+			{
+				Config: testAccArtifactRegistryRepository_createMvnEmpty1(repositoryID),
+			},
+			{
+				ResourceName:      "google_artifact_registry_repository.test",
+				ImportState:       true,
+				ImportStateVerify: true,
+			},
+			{
+				Config:             testAccArtifactRegistryRepository_createMvnEmpty2(repositoryID),
+				PlanOnly:           true,
+				ExpectNonEmptyPlan: false,
+			},
+			{
+				Config:             testAccArtifactRegistryRepository_createMvnEmpty3(repositoryID),
+				PlanOnly:           true,
+				ExpectNonEmptyPlan: false,
+			},
+		},
+	})
+}
+
 func TestAccArtifactRegistryRepository_kfp(t *testing.T) {
 	t.Parallel()
 
@@ -152,6 +184,43 @@ resource "google_artifact_registry_repository" "test" {
 `, repositoryID, versionPolicy)
 }
 
+func testAccArtifactRegistryRepository_createMvnEmpty1(repositoryID string) string {
+	return fmt.Sprintf(`
+resource "google_artifact_registry_repository" "test" {
+  repository_id = "%s"
+  location = "us-central1"
+  description = "maven repository with empty maven_config"
+  format = "MAVEN"
+}
+`, repositoryID)
+}
+
+func testAccArtifactRegistryRepository_createMvnEmpty2(repositoryID string) string {
+	return fmt.Sprintf(`
+resource "google_artifact_registry_repository" "test" {
+  repository_id = "%s"
+  location = "us-central1"
+  description = "maven repository with empty maven_config"
+  format = "MAVEN"
+  maven_config { }
+}
+`, repositoryID)
+}
+
+func testAccArtifactRegistryRepository_createMvnEmpty3(repositoryID string) string {
+	return fmt.Sprintf(`
+resource "google_artifact_registry_repository" "test" {
+  repository_id = "%s"
+  location = "us-central1"
+  description = "maven repository with empty maven_config"
+  format = "MAVEN"
+  maven_config {
+    allow_snapshot_overwrites = false
+  }
+}
+`, repositoryID)
+}
+
 func testAccArtifactRegistryRepository_kfp(repositoryID string) string {
 	return fmt.Sprintf(`
 resource "google_artifact_registry_repository" "test" {