backend-app-api: add module initialization test + fix

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/backend-app-api/src/wiring/BackendInitializer.test.ts

@@ -20,10 +20,15 @@ import {
   coreServices,
   createBackendPlugin,
   createBackendModule,
+  createExtensionPoint,
 } from '@backstage/backend-plugin-api';
 import { BackendInitializer } from './BackendInitializer';
 import { ServiceRegistry } from './ServiceRegistry';
-import { rootLifecycleServiceFactory } from '../services/implementations';
+import {
+  lifecycleServiceFactory,
+  loggerServiceFactory,
+  rootLifecycleServiceFactory,
+} from '../services/implementations';
 
 const rootRef = createServiceRef<{ x: number }>({
   id: '1',
@@ -44,6 +49,17 @@ class MockLogger {
   }
 }
 
+const baseFactories = [
+  lifecycleServiceFactory(),
+  rootLifecycleServiceFactory(),
+  createServiceFactory({
+    service: coreServices.rootLogger,
+    deps: {},
+    factory: () => new MockLogger(),
+  })(),
+  loggerServiceFactory(),
+];
+
 describe('BackendInitializer', () => {
   it('should initialize root scoped services', async () => {
     const rootFactory = jest.fn();
@@ -75,6 +91,65 @@ describe('BackendInitializer', () => {
     expect(pluginFactory).not.toHaveBeenCalled();
   });
 
+  it('should initialize modules with extension points', async () => {
+    expect.assertions(3);
+
+    const extensionPoint = createExtensionPoint<{ values: string[] }>({
+      id: 'a',
+    });
+    const init = new BackendInitializer(new ServiceRegistry(baseFactories));
+
+    init.add(
+      createBackendModule({
+        pluginId: 'test',
+        moduleId: 'modA',
+        register(reg) {
+          reg.registerInit({
+            deps: { extension: extensionPoint },
+            async init({ extension }) {
+              expect(extension.values).toEqual(['b']);
+              extension.values.push('a');
+            },
+          });
+        },
+      })(),
+    );
+
+    init.add(
+      createBackendModule({
+        pluginId: 'test',
+        moduleId: 'modB',
+        register(reg) {
+          const values = ['b'];
+          reg.registerExtensionPoint(extensionPoint, { values });
+          reg.registerInit({
+            deps: {},
+            async init() {
+              expect(values).toEqual(['b', 'a', 'c']);
+            },
+          });
+        },
+      })(),
+    );
+
+    init.add(
+      createBackendModule({
+        pluginId: 'test',
+        moduleId: 'modC',
+        register(reg) {
+          reg.registerInit({
+            deps: { extension: extensionPoint },
+            async init({ extension }) {
+              expect(extension.values).toEqual(['b', 'a']);
+              extension.values.push('c');
+            },
+          });
+        },
+      })(),
+    );
+    await init.start();
+  });
+
   it('should forward errors when plugins fail to start', async () => {
     const init = new BackendInitializer(new ServiceRegistry([]));
     init.add(

packages/backend-app-api/src/wiring/BackendInitializer.ts

@@ -216,8 +216,11 @@ export class BackendInitializer {
           const tree = DependencyTree.fromIterable(
             Array.from(modules).map(([id, { provides, consumes }]) => ({
               id,
-              provides: Array.from(provides).map(p => p.id),
-              consumes: Array.from(consumes).map(c => c.id),
+              // Relationships are reversed at this point since we're only interested in the extension points.
+              // If a modules provides extension point A we want it to be initialized AFTER all modules
+              // that depend on extension point A, so that they can provide their extensions.
+              consumes: Array.from(provides).map(p => p.id),
+              produces: Array.from(consumes).map(c => c.id),
             })),
           );
           const circular = tree.detectCircularDependency();