backend-app-api: stop loading modules if parent plugin is not present

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

.changeset/lazy-rats-fail.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-app-api': minor
+---
+
+**BREAKING**: Modules are no longer loaded unless the plugin that they extend is present.

.changeset/pink-mirrors-jam.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-test-utils': patch
+---
+
+`startTestBackend` will now add placeholder plugins when a modules are provided without their parent plugin.

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

@@ -60,6 +60,16 @@ const baseFactories = [
   loggerServiceFactory(),
 ];
 
+const testPlugin = createBackendPlugin({
+  pluginId: 'test',
+  register(reg) {
+    reg.registerInit({
+      deps: {},
+      async init() {},
+    });
+  },
+})();
+
 describe('BackendInitializer', () => {
   it('should initialize root scoped services', async () => {
     const rootFactory = jest.fn();
@@ -99,6 +109,7 @@ describe('BackendInitializer', () => {
     });
     const init = new BackendInitializer(baseFactories);
 
+    init.add(testPlugin);
     init.add(
       createBackendModule({
         pluginId: 'test',
@@ -172,6 +183,7 @@ describe('BackendInitializer', () => {
 
   it('should forward errors when modules fail to start', async () => {
     const init = new BackendInitializer([]);
+    init.add(testPlugin);
     init.add(
       createBackendModule({
         pluginId: 'test',
@@ -222,6 +234,7 @@ describe('BackendInitializer', () => {
 
   it('should reject duplicate modules', async () => {
     const init = new BackendInitializer([]);
+    init.add(testPlugin);
     init.add(
       createBackendModule({
         pluginId: 'test',
@@ -262,6 +275,7 @@ describe('BackendInitializer', () => {
         factory: () => new MockLogger(),
       })(),
     ]);
+    init.add(testPlugin);
     init.add(
       createBackendModule({
         pluginId: 'test',
@@ -308,9 +322,10 @@ describe('BackendInitializer', () => {
         },
       })(),
     );
+    init.add(testPlugin);
     init.add(
       createBackendModule({
-        pluginId: 'test-b',
+        pluginId: 'test',
         moduleId: 'mod',
         register(reg) {
           reg.registerInit({
@@ -321,7 +336,7 @@ describe('BackendInitializer', () => {
       })(),
     );
     await expect(init.start()).rejects.toThrow(
-      "Illegal dependency: Module 'mod' for plugin 'test-b' attempted to depend on extension point 'a' for plugin 'test-a'. Extension points can only be used within their plugin's scope.",
+      "Illegal dependency: Module 'mod' for plugin 'test' attempted to depend on extension point 'a' for plugin 'test-a'. Extension points can only be used within their plugin's scope.",
     );
   });
 });

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

@@ -228,9 +228,7 @@ export class BackendInitializer {
       }
     }
 
-    const allPluginIds = [
-      ...new Set([...pluginInits.keys(), ...moduleInits.keys()]),
-    ];
+    const allPluginIds = [...pluginInits.keys()];
 
     // All plugins are initialized in parallel
     await Promise.all(

packages/backend-test-utils/src/next/wiring/TestBackend.ts

@@ -29,6 +29,7 @@ import {
   ExtensionPoint,
   coreServices,
   createBackendModule,
+  createBackendPlugin,
 } from '@backstage/backend-plugin-api';
 import { mockServices } from '../services';
 import { ConfigReader } from '@backstage/config';
@@ -84,6 +85,42 @@ export const defaultServiceFactories = [
   mockServices.urlReader.factory(),
 ];
 
+/**
+ * Given a set of features, return an array of plugins that ensures that each
+ * module in the provided set of features has a corresponding plugin.
+ * @internal
+ */
+function createPluginsForOrphanModules(features: Array<BackendFeature>) {
+  const pluginIds = new Set<string>();
+  const modulePluginIds = new Set<string>();
+
+  for (const feature of features) {
+    if (isInternalBackendFeature(feature)) {
+      const registrations = feature.getRegistrations();
+      for (const registration of registrations) {
+        if (registration.type === 'plugin') {
+          pluginIds.add(registration.pluginId);
+        } else if (registration.type === 'module') {
+          modulePluginIds.add(registration.pluginId);
+        }
+      }
+    }
+  }
+
+  for (const pluginId of pluginIds) {
+    modulePluginIds.delete(pluginId);
+  }
+
+  return Array.from(modulePluginIds).map(pluginId =>
+    createBackendPlugin({
+      pluginId,
+      register(reg) {
+        reg.registerInit({ deps: {}, async init() {} });
+      },
+    }),
+  );
+}
+
 /**
  * Given a set of extension points and features, find the extension
  * points that we mock and tie them to the correct plugin ID.
@@ -277,7 +314,9 @@ export async function startTestBackend<TExtensionPoints extends any[]>(
   for (const m of createExtensionPointTestModules(features, extensionPoints)) {
     backend.add(m);
   }
-
+  for (const p of createPluginsForOrphanModules(features)) {
+    backend.add(p);
+  }
   for (const feature of features) {
     backend.add(feature);
   }