Add backstage.io/template-source annotation via the catalog:write action

Signed-off-by: Eric Peterson <ericpeterson@spotify.com>

.changeset/scaffolder-source-of-truth.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-scaffolder-backend': patch
+---
+
+The `catalog:write` action now automatically adds a `backstage.io/template-source` annotation, indicating which Scaffolder template was used to create the entity.

plugins/scaffolder-backend/src/scaffolder/actions/builtin/catalog/write.test.ts

@@ -94,4 +94,34 @@ describe('catalog:write', () => {
       yaml.stringify(entity),
     );
   });
+
+  it('should add backstage.io/source-template if provided', async () => {
+    const entity = {
+      apiVersion: 'backstage.io/v1alpha1',
+      kind: 'Component',
+      metadata: {
+        name: 'n',
+        namespace: 'ns',
+        annotations: {},
+      },
+      spec: {},
+    };
+
+    await action.handler({
+      ...mockContext,
+      templateInfo: { entityRef: 'template:default/test-skeleton' },
+      input: { entity },
+    });
+
+    const expectedEntity = JSON.parse(JSON.stringify(entity));
+    expectedEntity.metadata.annotations = {
+      'backstage.io/source-template': 'template:default/test-skeleton',
+    };
+
+    expect(fsMock.writeFile).toHaveBeenCalledTimes(1);
+    expect(fsMock.writeFile).toHaveBeenCalledWith(
+      resolvePath(mockContext.workspacePath, 'catalog-info.yaml'),
+      yaml.stringify(expectedEntity),
+    );
+  });
 });

plugins/scaffolder-backend/src/scaffolder/actions/builtin/catalog/write.ts

@@ -51,11 +51,25 @@ export function createCatalogWriteAction() {
     async handler(ctx) {
       ctx.logger.info(`Writing catalog-info.yaml`);
       const { filePath, entity } = ctx.input;
+      const entityRef = ctx.templateInfo?.entityRef;
       const path = filePath ?? 'catalog-info.yaml';
 
       await fs.writeFile(
         resolveSafeChildPath(ctx.workspacePath, path),
-        yaml.stringify(entity),
+        yaml.stringify({
+          ...entity,
+          metadata: {
+            ...entity.metadata,
+            ...(entityRef
+              ? {
+                  annotations: {
+                    ...entity.metadata.annotations,
+                    'backstage.io/source-template': entityRef,
+                  },
+                }
+              : undefined),
+          },
+        }),
       );
     },
   });