backend-plugin-api: make BackendFeature opaque

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

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

@@ -19,6 +19,7 @@ import {
   createBackendPlugin,
   createExtensionPoint,
 } from './factories';
+import { InternalBackendFeature } from './types';
 
 describe('createExtensionPoint', () => {
   it('should create an ExtensionPoint', () => {
@@ -34,11 +35,30 @@ describe('createBackendPlugin', () => {
   it('should create a BackendPlugin', () => {
     const plugin = createBackendPlugin((_options: { a: string }) => ({
       pluginId: 'x',
-      register() {},
+      register(r) {
+        r.registerInit({ deps: {}, async init() {} });
+      },
     }));
     expect(plugin).toBeDefined();
     expect(plugin({ a: 'a' })).toBeDefined();
-    expect(plugin({ a: 'a' }).id).toBe('x');
+    expect(plugin({ a: 'a' })).toEqual({
+      $$type: '@backstage/BackendFeature',
+      version: 'v1',
+      getRegistrations: expect.any(Function),
+    });
+    expect(
+      (plugin({ a: 'a' }) as InternalBackendFeature).getRegistrations(),
+    ).toEqual([
+      {
+        type: 'plugin',
+        pluginId: 'x',
+        extensionPoints: [],
+        init: {
+          deps: expect.any(Object),
+          func: expect.any(Function),
+        },
+      },
+    ]);
     // @ts-expect-error
     expect(plugin()).toBeDefined();
     // @ts-expect-error
@@ -79,7 +99,11 @@ describe('createBackendPlugin', () => {
     }));
     expect(plugin).toBeDefined();
     expect(plugin({ a: 'a' })).toBeDefined();
-    expect(plugin({ a: 'a' }).id).toBe('x');
+    expect(plugin({ a: 'a' })).toEqual({
+      $$type: '@backstage/BackendFeature',
+      version: 'v1',
+      getRegistrations: expect.any(Function),
+    });
     // @ts-expect-error
     expect(plugin()).toBeDefined();
     // @ts-expect-error
@@ -107,11 +131,30 @@ describe('createBackendModule', () => {
     const mod = createBackendModule((_options: { a: string }) => ({
       pluginId: 'x',
       moduleId: 'y',
-      register() {},
+      register(r) {
+        r.registerInit({ deps: {}, async init() {} });
+      },
     }));
     expect(mod).toBeDefined();
     expect(mod({ a: 'a' })).toBeDefined();
-    expect(mod({ a: 'a' }).id).toBe('x.y');
+    expect(mod({ a: 'a' })).toEqual({
+      $$type: '@backstage/BackendFeature',
+      version: 'v1',
+      getRegistrations: expect.any(Function),
+    });
+    expect(
+      (mod({ a: 'a' }) as InternalBackendFeature).getRegistrations(),
+    ).toEqual([
+      {
+        type: 'module',
+        pluginId: 'x',
+        moduleId: 'y',
+        init: {
+          deps: expect.any(Object),
+          func: expect.any(Function),
+        },
+      },
+    ]);
     // @ts-expect-error
     expect(mod()).toBeDefined();
     // @ts-expect-error
@@ -155,7 +198,11 @@ describe('createBackendModule', () => {
     }));
     expect(mod).toBeDefined();
     expect(mod({ a: 'a' })).toBeDefined();
-    expect(mod({ a: 'a' }).id).toBe('x.y');
+    expect(mod({ a: 'a' })).toEqual({
+      $$type: '@backstage/BackendFeature',
+      version: 'v1',
+      getRegistrations: expect.any(Function),
+    });
     // @ts-expect-error
     expect(mod()).toBeDefined();
     // @ts-expect-error

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

@@ -19,6 +19,9 @@ import {
   BackendPluginRegistrationPoints,
   BackendFeature,
   ExtensionPoint,
+  InternalBackendFeature,
+  InternalBackendModuleRegistration,
+  InternalBackendPluginRegistration,
 } from './types';
 
 /**
@@ -86,11 +89,59 @@ export function createBackendPlugin<TOptions extends [options?: object] = []>(
   config: BackendPluginConfig | ((...params: TOptions) => BackendPluginConfig),
 ): (...params: TOptions) => BackendFeature {
   const configCallback = typeof config === 'function' ? config : () => config;
-  return (...options: TOptions) => {
+  return (...options: TOptions): InternalBackendFeature => {
     const c = configCallback(...options);
+
+    let registrations: InternalBackendPluginRegistration[];
+
     return {
-      ...c,
-      id: c.pluginId,
+      $$type: '@backstage/BackendFeature',
+      version: 'v1',
+      getRegistrations() {
+        if (registrations) {
+          return registrations;
+        }
+        const extensionPoints: InternalBackendPluginRegistration['extensionPoints'] =
+          [];
+        let init: InternalBackendPluginRegistration['init'] | undefined =
+          undefined;
+
+        c.register({
+          registerExtensionPoint(ext, impl) {
+            if (init) {
+              throw new Error(
+                'registerExtensionPoint called after registerInit',
+              );
+            }
+            extensionPoints.push([ext, impl]);
+          },
+          registerInit(regInit) {
+            if (init) {
+              throw new Error('registerInit must only be called once');
+            }
+            init = {
+              deps: regInit.deps,
+              func: regInit.init,
+            };
+          },
+        });
+
+        if (!init) {
+          throw new Error(
+            `registerInit was not called by register in ${c.pluginId}`,
+          );
+        }
+
+        registrations = [
+          {
+            type: 'plugin',
+            pluginId: c.pluginId,
+            extensionPoints,
+            init,
+          },
+        ];
+        return registrations;
+      },
     };
   };
 }
@@ -127,11 +178,49 @@ export function createBackendModule<TOptions extends [options?: object] = []>(
   config: BackendModuleConfig | ((...params: TOptions) => BackendModuleConfig),
 ): (...params: TOptions) => BackendFeature {
   const configCallback = typeof config === 'function' ? config : () => config;
-  return (...options: TOptions) => {
+  return (...options: TOptions): InternalBackendFeature => {
     const c = configCallback(...options);
+
+    let registrations: InternalBackendModuleRegistration[];
+
     return {
-      id: `${c.pluginId}.${c.moduleId}`,
-      register: c.register,
+      $$type: '@backstage/BackendFeature',
+      version: 'v1',
+      getRegistrations() {
+        if (registrations) {
+          return registrations;
+        }
+        let init: InternalBackendModuleRegistration['init'] | undefined =
+          undefined;
+
+        c.register({
+          registerInit(regInit) {
+            if (init) {
+              throw new Error('registerInit must only be called once');
+            }
+            init = {
+              deps: regInit.deps,
+              func: regInit.init,
+            };
+          },
+        });
+
+        if (!init) {
+          throw new Error(
+            `registerInit was not called by register in ${c.moduleId} module for ${c.pluginId}`,
+          );
+        }
+
+        registrations = [
+          {
+            type: 'module',
+            pluginId: c.pluginId,
+            moduleId: c.moduleId,
+            init,
+          },
+        ];
+        return registrations;
+      },
     };
   };
 }

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

@@ -32,7 +32,6 @@ export {
 export type {
   BackendModuleRegistrationPoints,
   BackendPluginRegistrationPoints,
-  BackendRegistrationPoints,
   BackendFeature,
   ExtensionPoint,
 } from './types';

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

@@ -35,26 +35,6 @@ export type ExtensionPoint<T> = {
   $$type: '@backstage/ExtensionPoint';
 };
 
-/**
- * The callbacks passed to the `register` method of a backend feature; this is
- * essentially a superset of {@link BackendPluginRegistrationPoints} and
- * {@link BackendModuleRegistrationPoints}.
- *
- * @public
- */
-export interface BackendRegistrationPoints {
-  registerExtensionPoint<TExtensionPoint>(
-    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>;
-  }): void;
-}
-
 /**
  * The callbacks passed to the `register` method of a backend plugin.
  *
@@ -89,7 +69,36 @@ export interface BackendModuleRegistrationPoints {
 
 /** @public */
 export interface BackendFeature {
-  // TODO(Rugvip): Try to get rid of the ID at this level, allowing for a feature to register multiple features as a bundle
-  id: string;
-  register(reg: BackendRegistrationPoints): void;
+  // NOTE: This type is opaque in order to simplify future API evolution.
+  $$type: '@backstage/BackendFeature';
+}
+
+/** @internal */
+export interface InternalBackendFeature extends BackendFeature {
+  version: 'v1';
+  getRegistrations(): Array<
+    InternalBackendPluginRegistration | InternalBackendModuleRegistration
+  >;
+}
+
+/** @internal */
+export interface InternalBackendPluginRegistration {
+  pluginId: string;
+  type: 'plugin';
+  extensionPoints: Array<readonly [ExtensionPoint<unknown>, unknown]>;
+  init: {
+    deps: Record<string, ServiceRef<unknown>>;
+    func(deps: Record<string, unknown>): Promise<void>;
+  };
+}
+
+/** @internal */
+export interface InternalBackendModuleRegistration {
+  pluginId: string;
+  moduleId: string;
+  type: 'module';
+  init: {
+    deps: Record<string, ServiceRef<unknown> | ExtensionPoint<unknown>>;
+    func(deps: Record<string, unknown>): Promise<void>;
+  };
 }