Merge pull request #19897 from backstage/mob/extensionTree

frontend-app-api: Add Extension utilities

packages/frontend-app-api/api-report.md

@@ -4,7 +4,9 @@
 
 ```ts
 import { BackstagePlugin } from '@backstage/frontend-plugin-api';
+import { Config } from '@backstage/config';
 import { ConfigApi } from '@backstage/core-plugin-api';
+import { ExtensionDataRef } from '@backstage/frontend-plugin-api';
 import { JSX as JSX_2 } from 'react';
 
 // @public (undocumented)
@@ -14,4 +16,23 @@ export function createApp(options: {
 }): {
   createRoot(): JSX_2.Element;
 };
+
+// @public (undocumented)
+export function createExtensionTree(options: { config: Config }): ExtensionTree;
+
+// @public (undocumented)
+export interface ExtensionTree {
+  // (undocumented)
+  getExtension(id: string): ExtensionTreeNode | undefined;
+  // (undocumented)
+  getExtensionAttachments(id: string, inputName: string): ExtensionTreeNode[];
+}
+
+// @public (undocumented)
+export interface ExtensionTreeNode {
+  // (undocumented)
+  getData<T>(ref: ExtensionDataRef<T>): T | undefined;
+  // (undocumented)
+  id: string;
+}
 ```

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

@@ -15,10 +15,11 @@
  */
 
 import React, { JSX } from 'react';
-import { ConfigReader } from '@backstage/config';
+import { ConfigReader, Config } from '@backstage/config';
 import {
   BackstagePlugin,
   coreExtensionData,
+  ExtensionDataRef,
 } from '@backstage/frontend-plugin-api';
 import { Core } from '../extensions/Core';
 import { CoreRoutes } from '../extensions/CoreRoutes';
@@ -76,26 +77,55 @@ import {
 import { BrowserRouter } from 'react-router-dom';
 
 /** @public */
-export function createApp(options: {
-  plugins: BackstagePlugin[];
-  config?: ConfigApi;
-}): {
-  createRoot(): JSX.Element;
-} {
-  const appConfig =
-    options?.config ??
-    ConfigReader.fromConfigs(overrideBaseUrlConfigs(defaultConfigLoaderSync()));
+export interface ExtensionTreeNode {
+  id: string;
+  getData<T>(ref: ExtensionDataRef<T>): T | undefined;
+}
 
+/** @public */
+export interface ExtensionTree {
+  getExtension(id: string): ExtensionTreeNode | undefined;
+  getExtensionAttachments(id: string, inputName: string): ExtensionTreeNode[];
+}
+
+/** @public */
+export function createExtensionTree(options: {
+  config: Config;
+}): ExtensionTree {
+  const plugins = getAvailablePlugins();
+  const { instances } = createInstances({
+    plugins,
+    config: options.config,
+  });
+
+  return {
+    getExtension(id: string): ExtensionTreeNode | undefined {
+      return instances.get(id);
+    },
+    getExtensionAttachments(
+      id: string,
+      inputName: string,
+    ): ExtensionTreeNode[] {
+      return instances.get(id)?.attachments.get(inputName) ?? [];
+    },
+  };
+}
+
+/**
+ * @internal
+ */
+export function createInstances(options: {
+  plugins: BackstagePlugin[];
+  config: Config;
+}) {
   const builtinExtensions = [Core, CoreRoutes, CoreNav, CoreLayout];
-  const discoveredPlugins = getAvailablePlugins();
-  const allPlugins = [...discoveredPlugins, ...options.plugins];
 
   // pull in default extension instance from discovered packages
   // apply config to adjust default extension instances and add more
   const extensionParams = mergeExtensionParameters({
-    sources: allPlugins,
+    sources: options.plugins,
     builtinExtensions,
-    parameters: readAppExtensionParameters(appConfig),
+    parameters: readAppExtensionParameters(options.config),
   });
 
   // TODO: validate the config of all extension instances
@@ -156,10 +186,32 @@ export function createApp(options: {
   }
 
   const rootConfigs = attachmentMap.get('root')?.get('default') ?? [];
+
   const rootInstances = rootConfigs.map(instanceParams =>
     createInstance(instanceParams),
   );
 
+  return { instances, rootInstances };
+}
+
+/** @public */
+export function createApp(options: {
+  plugins: BackstagePlugin[];
+  config?: ConfigApi;
+}): {
+  createRoot(): JSX.Element;
+} {
+  const discoveredPlugins = getAvailablePlugins();
+  const allPlugins = [...discoveredPlugins, ...options.plugins];
+  const appConfig =
+    options?.config ??
+    ConfigReader.fromConfigs(overrideBaseUrlConfigs(defaultConfigLoaderSync()));
+
+  const { rootInstances } = createInstances({
+    plugins: allPlugins,
+    config: appConfig,
+  });
+
   const routePaths = extractRouteInfoFromInstanceTree(rootInstances);
 
   const coreInstance = rootInstances.find(({ id }) => id === 'core');

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

@@ -14,4 +14,9 @@
  * limitations under the License.
  */
 
-export { createApp } from './createApp';
+export {
+  createApp,
+  createExtensionTree,
+  type ExtensionTreeNode,
+  type ExtensionTree,
+} from './createApp';