Merge pull request #19787 from backstage/mob/package-discovery

cli,frontend-app-api: add experimental support for frontend package discovery

packages/frontend-app-api/src/createApp.tsx

@@ -32,6 +32,7 @@ import {
 } from './wiring/parameters';
 import { RoutingProvider } from './routing/RoutingContext';
 import { RouteRef } from '@backstage/core-plugin-api';
+import { getAvailablePlugins } from './wiring/discovery';
 
 /** @public */
 export function createApp(options: { plugins: BackstagePlugin[] }): {
@@ -40,11 +41,12 @@ export function createApp(options: { plugins: BackstagePlugin[] }): {
   const appConfig = ConfigReader.fromConfigs(process.env.APP_CONFIG as any);
 
   const builtinExtensions = [CoreRouter];
+  const discoveredPlugins = getAvailablePlugins();
 
   // pull in default extension instance from discovered packages
   // apply config to adjust default extension instances and add more
   const extensionParams = mergeExtensionParameters({
-    sources: options.plugins,
+    sources: [...options.plugins, ...discoveredPlugins],
     builtinExtensions,
     parameters: readAppExtensionParameters(appConfig),
   });

packages/frontend-app-api/src/wiring/discovery.test.ts

@@ -0,0 +1,118 @@
+/*
+ * 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 { createPlugin } from '@backstage/frontend-plugin-api';
+import { getAvailablePlugins } from './discovery';
+
+const globalSpy = jest.fn();
+Object.defineProperty(global, '__@backstage/discovered__', {
+  get: globalSpy,
+});
+
+describe('getAvailablePlugins', () => {
+  afterEach(jest.resetAllMocks);
+
+  it('should discover nothing with undefined global', () => {
+    expect(getAvailablePlugins()).toEqual([]);
+  });
+
+  it('should discover nothing with empty global', () => {
+    globalSpy.mockReturnValue({
+      modules: [],
+    });
+    expect(getAvailablePlugins()).toEqual([]);
+  });
+
+  it('should discover a plugin', () => {
+    const testPlugin = createPlugin({ id: 'test' });
+    globalSpy.mockReturnValue({
+      modules: [
+        {
+          module: {
+            testPlugin,
+          },
+        },
+      ],
+    });
+    expect(getAvailablePlugins()).toEqual([testPlugin]);
+  });
+
+  it('should ignore garbage', () => {
+    const testPlugin = createPlugin({ id: 'test' });
+    globalSpy.mockReturnValue({
+      modules: [
+        {
+          module: {
+            testPlugin,
+            a: 'a',
+            b: null,
+            c: undefined,
+            d: Symbol('wat'),
+            e: () => {},
+            f: [],
+            g: {},
+            h: class {},
+            i: NaN,
+            j: Infinity,
+            k: -Infinity,
+            l: new Date(),
+            m: new RegExp('wat'),
+            n: new Error('wat'),
+            o: new Map(),
+            p: new Set(),
+            q: new WeakMap(),
+            r: new WeakSet(),
+            s: new ArrayBuffer(1),
+            t: new DataView(new ArrayBuffer(1)),
+            u: false,
+            v: true,
+            w: 0,
+            x: 1,
+            y: -1,
+            z: '',
+          },
+        },
+      ],
+    });
+    expect(getAvailablePlugins()).toEqual([testPlugin]);
+  });
+
+  it('should discover multiple plugins', () => {
+    const test1Plugin = createPlugin({ id: 'test1' });
+    const test2Plugin = createPlugin({ id: 'test2' });
+    const test3Plugin = createPlugin({ id: 'test3' });
+    globalSpy.mockReturnValue({
+      modules: [
+        {
+          module: {
+            test1Plugin,
+            test2Plugin,
+          },
+        },
+        {
+          module: {
+            test3Plugin,
+          },
+        },
+      ],
+    });
+    expect(getAvailablePlugins()).toEqual([
+      test1Plugin,
+      test2Plugin,
+      test3Plugin,
+    ]);
+  });
+});

packages/frontend-app-api/src/wiring/discovery.ts

@@ -0,0 +1,43 @@
+/*
+ * 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 { BackstagePlugin } from '@backstage/frontend-plugin-api';
+
+interface DiscoveryGlobal {
+  modules: Array<{ name: string; module: object }>;
+}
+
+/**
+ * @public
+ */
+export function getAvailablePlugins(): BackstagePlugin[] {
+  const discovered = (
+    window as { '__@backstage/discovered__'?: DiscoveryGlobal }
+  )['__@backstage/discovered__'];
+
+  return (
+    discovered?.modules.flatMap(({ module: mod }) =>
+      Object.values(mod).filter(isBackstagePlugin),
+    ) ?? []
+  );
+}
+
+function isBackstagePlugin(obj: unknown): obj is BackstagePlugin {
+  if (obj !== null && typeof obj === 'object' && '$$type' in obj) {
+    return obj.$$type === 'backstage-plugin';
+  }
+  return false;
+}