frontend-app-api: implement package discovery

Co-authored-by: Philipp Hugenroth <philipph@spotify.com>
Co-authored-by: Johan Haals <johan.haals@gmail.com>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

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 './discover';
 
 /** @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/discover/discover-plugins.d.ts

@@ -0,0 +1,22 @@
+/*
+ * 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.
+ */
+declare module '__backstage-autodetected-plugins__' {
+  type DetectedModule = {
+    name: string;
+    module: Record<string, any>;
+  };
+  const modules: Array<{ name: string; module: Record<string, any> }>;
+}

packages/frontend-app-api/src/discover/index.ts

@@ -0,0 +1,36 @@
+/*
+ * 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';
+
+// eslint-disable-next-line @backstage/no-undeclared-imports
+import { modules } from '__backstage-autodetected-plugins__';
+
+/**
+ * @public
+ */
+export function getAvailablePlugins(): BackstagePlugin[] {
+  return modules.flatMap(({ module: mod }) =>
+    Object.values(mod).flatMap(val => (isBackstagePlugin(val) ? [val] : [])),
+  );
+}
+
+function isBackstagePlugin(obj: unknown): obj is BackstagePlugin {
+  if (obj !== null && typeof obj === 'object' && '$$type' in obj) {
+    return obj.$$type === 'backstage-plugin';
+  }
+  return false;
+}