backend-app-api: throw error if trying to override metadata service

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

.changeset/great-forks-lay.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-app-api': patch
+---
+
+An error will now be thrown if attempting to override the plugin metadata service.

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

@@ -19,6 +19,7 @@ import {
   BackendFeature,
   ExtensionPoint,
   ServiceRef,
+  coreServices,
 } from '@backstage/backend-plugin-api';
 import { BackstageBackend } from './BackstageBackend';
 
@@ -80,6 +81,11 @@ export function createSpecializedBackend(
     const ids = Array.from(duplicates).join(', ');
     throw new Error(`Duplicate service implementations provided for ${ids}`);
   }
+  if (exists.has(coreServices.pluginMetadata.id)) {
+    throw new Error(
+      `The ${coreServices.pluginMetadata.id} service cannot be overridden`,
+    );
+  }
 
   return new BackstageBackend(services);
 }

packages/backend-defaults/src/CreateBackend.test.ts

@@ -55,4 +55,18 @@ describe('createBackend', () => {
       'Duplicate service implementations provided for core.rootLifecycle',
     );
   });
+
+  it('should throw when providing a plugin metadata service implementation', () => {
+    expect(() =>
+      createBackend({
+        services: [
+          createServiceFactory({
+            service: coreServices.pluginMetadata,
+            deps: {},
+            factory: async () => async () => ({ getId: () => 'test' }),
+          }),
+        ],
+      }),
+    ).toThrow('The core.plugin-metadata service cannot be overridden');
+  });
 });