backend-plugin-api: fix for plugins and modules depending on multion services

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

packages/backend-plugin-api/src/wiring/createBackendModule.test.ts

@@ -14,7 +14,9 @@
  * limitations under the License.
  */
 
+import { createServiceRef } from '../services';
 import { createBackendModule } from './createBackendModule';
+import { createExtensionPoint } from './createExtensionPoint';
 import { InternalBackendRegistrations } from './types';
 
 describe('createBackendModule', () => {
@@ -54,4 +56,35 @@ describe('createBackendModule', () => {
     // @ts-expect-error
     expect(module({ a: 'a' })).toBeDefined();
   });
+
+  it('should be able to depend on all types of dependencies', () => {
+    const extensionPoint = createExtensionPoint<string>({ id: 'point' });
+    const singleServiceRef = createServiceRef<string>({ id: 'single' });
+    const multiServiceRef = createServiceRef<string>({
+      id: 'multi',
+      multiton: true,
+    });
+
+    const plugin = createBackendModule({
+      pluginId: 'x',
+      moduleId: 'y',
+      register(r) {
+        r.registerInit({
+          deps: {
+            point: extensionPoint,
+            single: singleServiceRef,
+            multi: multiServiceRef,
+          },
+          async init({ point, single, multi }) {
+            const a: string = point;
+            const b: string = single;
+            const c: string[] = multi;
+            expect([a, b, c]).toBe('unused');
+          },
+        });
+      },
+    });
+
+    expect(plugin.$$type).toEqual('@backstage/BackendFeature');
+  });
 });

packages/backend-plugin-api/src/wiring/createBackendPlugin.test.ts

@@ -14,7 +14,9 @@
  * limitations under the License.
  */
 
+import { createServiceRef } from '../services';
 import { createBackendPlugin } from './createBackendPlugin';
+import { createExtensionPoint } from './createExtensionPoint';
 import { InternalBackendRegistrations } from './types';
 
 describe('createBackendPlugin', () => {
@@ -52,4 +54,50 @@ describe('createBackendPlugin', () => {
     // @ts-expect-error
     expect(plugin({ a: 'a' })).toBeDefined();
   });
+
+  it('should be able to depend on all compatible dependencies', () => {
+    const singleServiceRef = createServiceRef<string>({ id: 'single' });
+    const multiServiceRef = createServiceRef<string>({
+      id: 'multi',
+      multiton: true,
+    });
+
+    const plugin = createBackendPlugin({
+      pluginId: 'x',
+      register(r) {
+        r.registerInit({
+          deps: {
+            single: singleServiceRef,
+            multi: multiServiceRef,
+          },
+          async init({ single, multi }) {
+            const a: string = single;
+            const b: string[] = multi;
+            expect([a, b]).toBe('unused');
+          },
+        });
+      },
+    });
+
+    expect(plugin.$$type).toEqual('@backstage/BackendFeature');
+  });
+
+  it('should not be able to depend on extension points', () => {
+    const extensionPoint = createExtensionPoint<string>({ id: 'point' });
+
+    const plugin = createBackendPlugin({
+      pluginId: 'x',
+      register(r) {
+        r.registerInit({
+          deps: {
+            // @ts-expect-error
+            point: extensionPoint,
+          },
+          async init() {},
+        });
+      },
+    });
+
+    expect(plugin.$$type).toEqual('@backstage/BackendFeature');
+  });
 });

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

@@ -36,6 +36,17 @@ export type ExtensionPoint<T> = {
   $$type: '@backstage/ExtensionPoint';
 };
 
+/** @ignore */
+type DepsToInstances<
+  TDeps extends {
+    [key in string]: ServiceRef<unknown> | ExtensionPoint<unknown>;
+  },
+> = {
+  [key in keyof TDeps]: TDeps[key] extends ServiceRef<unknown, any, 'multiton'>
+    ? Array<TDeps[key]['T']>
+    : TDeps[key]['T'];
+};
+
 /**
  * The callbacks passed to the `register` method of a backend plugin.
  *
@@ -46,11 +57,13 @@ export interface BackendPluginRegistrationPoints {
     ref: ExtensionPoint<TExtensionPoint>,
     impl: TExtensionPoint,
   ): void;
-  registerInit<Deps extends { [name in string]: unknown }>(options: {
-    deps: {
-      [name in keyof Deps]: ServiceRef<Deps[name]>;
-    };
-    init(deps: Deps): Promise<void>;
+  registerInit<
+    TDeps extends {
+      [name in string]: ServiceRef<unknown>;
+    },
+  >(options: {
+    deps: TDeps;
+    init(deps: DepsToInstances<TDeps>): Promise<void>;
   }): void;
 }
 
@@ -64,11 +77,13 @@ export interface BackendModuleRegistrationPoints {
     ref: ExtensionPoint<TExtensionPoint>,
     impl: TExtensionPoint,
   ): void;
-  registerInit<Deps extends { [name in string]: unknown }>(options: {
-    deps: {
-      [name in keyof Deps]: ServiceRef<Deps[name]> | ExtensionPoint<Deps[name]>;
-    };
-    init(deps: Deps): Promise<void>;
+  registerInit<
+    TDeps extends {
+      [name in string]: ServiceRef<unknown> | ExtensionPoint<unknown>;
+    },
+  >(options: {
+    deps: TDeps;
+    init(deps: DepsToInstances<TDeps>): Promise<void>;
   }): void;
 }