Merge pull request #15743 from backstage/mob/environments

backend-app-api: add shared environments

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

@@ -16,10 +16,17 @@
 
 import {
   coreServices,
+  createBackendPlugin,
   createServiceFactory,
+  createServiceRef,
+  createSharedEnvironment,
 } from '@backstage/backend-plugin-api';
+import { mockConfigFactory } from '@backstage/backend-test-utils';
 import { createBackend } from './CreateBackend';
 
+const fooServiceRef = createServiceRef<string>({ id: 'foo', scope: 'root' });
+const barServiceRef = createServiceRef<string>({ id: 'bar', scope: 'root' });
+
 describe('createBackend', () => {
   it('should not throw when overriding a default service implementation', () => {
     expect(() =>
@@ -69,4 +76,91 @@ describe('createBackend', () => {
       }),
     ).toThrow('The core.pluginMetadata service cannot be overridden');
   });
+
+  it('should throw if an unsupported InternalSharedEnvironment version is passed in', () => {
+    expect(() =>
+      createBackend({
+        env: {} as any,
+      }),
+    ).toThrow(
+      "Shared environment version 'undefined' is invalid or not supported",
+    );
+    expect(() =>
+      createBackend({
+        env: { version: {} } as any,
+      }),
+    ).toThrow(
+      "Shared environment version '[object Object]' is invalid or not supported",
+    );
+    expect(() =>
+      createBackend({
+        env: { version: 'v2' } as any,
+      }),
+    ).toThrow("Shared environment version 'v2' is invalid or not supported");
+  });
+
+  it('should prioritize services correctly', async () => {
+    const backend = createBackend({
+      env: createSharedEnvironment({
+        services: [
+          createServiceFactory({
+            service: coreServices.rootHttpRouter,
+            deps: {},
+            async factory() {
+              return {
+                use() {},
+              };
+            },
+          }),
+          mockConfigFactory({
+            data: { root: 'root-env' },
+          }),
+          createServiceFactory({
+            service: fooServiceRef,
+            deps: {},
+            async factory() {
+              return 'foo-env';
+            },
+          }),
+          createServiceFactory({
+            service: barServiceRef,
+            deps: {},
+            async factory() {
+              return 'bar-env';
+            },
+          }),
+        ],
+      })(),
+      services: [
+        createServiceFactory({
+          service: fooServiceRef,
+          deps: {},
+          factory: async () => 'foo-backend',
+        }),
+      ],
+    });
+
+    expect.assertions(3);
+    backend.add(
+      createBackendPlugin({
+        id: 'test',
+        register(reg) {
+          reg.registerInit({
+            deps: {
+              config: coreServices.config,
+              foo: fooServiceRef,
+              bar: barServiceRef,
+            },
+            async init({ config, foo, bar }) {
+              expect(config.get('root')).toBe('root-env');
+              expect(foo).toBe('foo-backend');
+              expect(bar).toBe('bar-env');
+            },
+          });
+        },
+      })(),
+    );
+
+    await backend.start();
+  });
 });

packages/backend-defaults/src/CreateBackend.ts

@@ -33,7 +33,15 @@ import {
   urlReaderFactory,
   identityFactory,
 } from '@backstage/backend-app-api';
-import { ServiceFactoryOrFunction } from '@backstage/backend-plugin-api';
+import {
+  ServiceFactory,
+  ServiceFactoryOrFunction,
+  SharedBackendEnvironment,
+} from '@backstage/backend-plugin-api';
+
+// Internal import of the type to avoid needing to export this.
+// eslint-disable-next-line monorepo/no-internal-import
+import type { InternalSharedBackendEnvironment } from '@backstage/backend-plugin-api/src/wiring/createSharedEnvironment';
 
 export const defaultServiceFactories = [
   cacheFactory(),
@@ -57,6 +65,7 @@ export const defaultServiceFactories = [
  * @public
  */
 export interface CreateBackendOptions {
+  env?: SharedBackendEnvironment;
   services?: ServiceFactoryOrFunction[];
 }
 
@@ -64,15 +73,35 @@ export interface CreateBackendOptions {
  * @public
  */
 export function createBackend(options?: CreateBackendOptions): Backend {
+  const services = new Array<ServiceFactory>();
+
+  // Highest priority: Services passed directly to createBackend
   const providedServices = (options?.services ?? []).map(sf =>
     typeof sf === 'function' ? sf() : sf,
   );
-  const providedIds = new Set(providedServices.map(sf => sf.service.id));
-  const neededDefaultFactories = defaultServiceFactories.filter(
-    sf => !providedIds.has(sf.service.id),
-  );
+  services.push(...providedServices);
 
-  return createSpecializedBackend({
-    services: [...neededDefaultFactories, ...providedServices],
-  });
+  // Middle priority: Services from the shared environment
+  if (options?.env) {
+    const env = options.env as unknown as InternalSharedBackendEnvironment;
+    if (env.version !== 'v1') {
+      throw new Error(
+        `Shared environment version '${env.version}' is invalid or not supported`,
+      );
+    }
+
+    const environmentServices =
+      env.services?.filter(
+        sf => !services.some(({ service }) => sf.service.id === service.id),
+      ) ?? [];
+    services.push(...environmentServices);
+  }
+
+  // Lowest priority: Default services that are not already provided by environment or directly to createBackend
+  const defaultServices = defaultServiceFactories.filter(
+    sf => !services.some(({ service }) => service.id === sf.service.id),
+  );
+  services.push(...defaultServices);
+
+  return createSpecializedBackend({ services });
 }