Merge pull request #15743 from backstage/mob/environments

backend-app-api: add shared environments

packages/backend-plugin-api/api-report.md

@@ -217,6 +217,15 @@ export function createServiceRef<TService>(
   config: ServiceRefConfig<TService, 'root'>,
 ): ServiceRef<TService, 'root'>;
 
+// @public
+export function createSharedEnvironment<
+  TOptions extends [options?: object] = [],
+>(
+  config:
+    | SharedBackendEnvironmentConfig
+    | ((...params: TOptions) => SharedBackendEnvironmentConfig),
+): (...options: TOptions) => SharedBackendEnvironment;
+
 // @public
 export interface DatabaseService {
   getClient(): Promise<Knex>;
@@ -467,6 +476,18 @@ export interface ServiceRefConfig<TService, TScope extends 'root' | 'plugin'> {
   scope?: TScope;
 }
 
+// @public (undocumented)
+export interface SharedBackendEnvironment {
+  // (undocumented)
+  $$type: 'SharedBackendEnvironment';
+}
+
+// @public (undocumented)
+export interface SharedBackendEnvironmentConfig {
+  // (undocumented)
+  services?: ServiceFactoryOrFunction[];
+}
+
 // @public
 export interface TokenManagerService {
   authenticate(token: string): Promise<void>;

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

@@ -0,0 +1,100 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {
+  createServiceFactory,
+  createServiceRef,
+  ServiceFactoryOrFunction,
+} from '../services';
+import {
+  createSharedEnvironment,
+  InternalSharedBackendEnvironment,
+} from './createSharedEnvironment';
+
+const fooService = createServiceRef<string>({ id: 'foo', scope: 'root' });
+const fooFactory = createServiceFactory({
+  service: fooService,
+  deps: {},
+  async factory() {
+    return 'foo';
+  },
+});
+
+const barService = createServiceRef<number>({ id: 'bar', scope: 'root' });
+const barFactory = createServiceFactory({
+  service: barService,
+  deps: {},
+  async factory() {
+    return 0xba5;
+  },
+});
+
+describe('createSharedEnvironment', () => {
+  it('should create an empty shared environment', () => {
+    const env = createSharedEnvironment({});
+    expect(env).toBeDefined();
+    const internalEnv = env() as unknown as InternalSharedBackendEnvironment;
+    expect(internalEnv).toEqual({
+      $$type: 'SharedBackendEnvironment',
+      version: 'v1',
+      services: undefined,
+    });
+  });
+
+  it('should create a shared environment with services', () => {
+    const env = createSharedEnvironment({
+      services: [fooFactory, barFactory()],
+    });
+    const internalEnv = env() as unknown as InternalSharedBackendEnvironment;
+    expect(internalEnv.version).toBe('v1');
+    expect(internalEnv.services?.length).toBe(2);
+    expect(internalEnv.services?.[0]?.service.id).toBe('foo');
+    expect(internalEnv.services?.[1]?.service.id).toBe('bar');
+  });
+
+  it('should create a shared environment with options', () => {
+    const env = createSharedEnvironment((options?: { withFoo?: boolean }) => {
+      const services = new Array<ServiceFactoryOrFunction>();
+      if (options?.withFoo) {
+        services.push(fooFactory());
+      }
+      services.push(barFactory);
+      return { services };
+    });
+    const internalEnv1 = env() as unknown as InternalSharedBackendEnvironment;
+    expect(internalEnv1.version).toBe('v1');
+    expect(internalEnv1.services?.length).toBe(1);
+    expect(internalEnv1.services?.[0]?.service.id).toBe('bar');
+
+    const internalEnv2 = env({
+      withFoo: true,
+    }) as unknown as InternalSharedBackendEnvironment;
+    expect(internalEnv2.version).toBe('v1');
+    expect(internalEnv2.services?.length).toBe(2);
+    expect(internalEnv2.services?.[0]?.service.id).toBe('foo');
+    expect(internalEnv2.services?.[1]?.service.id).toBe('bar');
+  });
+
+  it('should not allow duplicate service factories', () => {
+    expect(() =>
+      createSharedEnvironment({
+        services: [fooFactory, fooFactory()],
+      })(),
+    ).toThrow(
+      "Duplicate service implementations provided in shared environment for 'foo'",
+    );
+  });
+});

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

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { ServiceFactory, ServiceFactoryOrFunction } from '../services';
+
+/** @public */
+export interface SharedBackendEnvironmentConfig {
+  services?: ServiceFactoryOrFunction[];
+}
+
+// This type is opaque in order to allow for future API evolution without
+// cluttering the external API. For example we might want to add support
+// for more powerful callback based backend modifications.
+//
+// By making this opaque we also ensure that the type doesn't become an input
+// type that we need to care about, as it would otherwise be possible to pass
+// a custom environment definition to `createBackend`, which we don't want.
+/**
+ * @public
+ */
+export interface SharedBackendEnvironment {
+  $$type: 'SharedBackendEnvironment';
+}
+
+/**
+ * This type is NOT supposed to be used by anyone except internally by the backend-app-api package.
+ * @internal */
+export interface InternalSharedBackendEnvironment {
+  version: 'v1';
+  services?: ServiceFactory[];
+}
+
+/**
+ * Creates a shared backend environment which can be used to create multiple backends
+ * @public
+ */
+export function createSharedEnvironment<
+  TOptions extends [options?: object] = [],
+>(
+  config:
+    | SharedBackendEnvironmentConfig
+    | ((...params: TOptions) => SharedBackendEnvironmentConfig),
+): (...options: TOptions) => SharedBackendEnvironment {
+  const configCallback = typeof config === 'function' ? config : () => config;
+
+  return (...options) => {
+    const actualConfig = configCallback(...options);
+    const services = actualConfig?.services?.map(sf =>
+      typeof sf === 'function' ? sf() : sf,
+    );
+
+    const exists = new Set<string>();
+    const duplicates = new Set<string>();
+    for (const { service } of services ?? []) {
+      if (exists.has(service.id)) {
+        duplicates.add(service.id);
+      } else {
+        exists.add(service.id);
+      }
+    }
+
+    if (duplicates.size > 0) {
+      const dupStr = [...duplicates].map(id => `'${id}'`).join(', ');
+      throw new Error(
+        `Duplicate service implementations provided in shared environment for ${dupStr}`,
+      );
+    }
+
+    // Here to ensure type safety in this internal implementation.
+    const env: SharedBackendEnvironment & InternalSharedBackendEnvironment = {
+      $$type: 'SharedBackendEnvironment',
+      version: 'v1',
+      services,
+    };
+    return env;
+  };
+}

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

@@ -14,6 +14,11 @@
  * limitations under the License.
  */
 
+export { createSharedEnvironment } from './createSharedEnvironment';
+export type {
+  SharedBackendEnvironment,
+  SharedBackendEnvironmentConfig,
+} from './createSharedEnvironment';
 export type {
   BackendModuleConfig,
   BackendPluginConfig,