core-api: make it possible for plugins to include ApiFactories

packages/core-api/src/app/App.tsx

@@ -324,6 +324,18 @@ export class PrivateAppImpl implements BackstageApp {
       registry.register('default', factory);
     }
 
+    for (const plugin of this.plugins) {
+      for (const factory of plugin.getApis()) {
+        if (!registry.register('default', factory)) {
+          throw new Error(
+            `Plugin ${plugin.getId()} tried to register duplicate or forbidden API factory for ${
+              factory.implements
+            }`,
+          );
+        }
+      }
+    }
+
     for (const factory of this.apis) {
       if (!registry.register('app', factory)) {
         throw new Error(

packages/core-api/src/plugin/Plugin.tsx

@@ -24,9 +24,11 @@ import {
 } from './types';
 import { validateBrowserCompat, validateFlagName } from '../app/FeatureFlags';
 import { RouteRef } from '../routing';
+import { AnyApiFactory } from '../apis';
 
 export type PluginConfig = {
   id: string;
+  apis?: Iterable<AnyApiFactory>;
   register?(hooks: PluginHooks): void;
 };
 
@@ -65,6 +67,10 @@ export class PluginImpl {
     return this.config.id;
   }
 
+  getApis(): Iterable<AnyApiFactory> {
+    return this.config.apis ?? [];
+  }
+
   output(): PluginOutput[] {
     if (this.storedOutput) {
       return this.storedOutput;

packages/core-api/src/plugin/types.ts

@@ -16,6 +16,7 @@
 
 import { ComponentType } from 'react';
 import { RouteRef } from '../routing';
+import { AnyApiFactory } from '../apis';
 
 export type RouteOptions = {
   // Whether the route path must match exactly, defaults to true.
@@ -70,4 +71,5 @@ export type PluginOutput =
 export type BackstagePlugin = {
   getId(): string;
   output(): PluginOutput[];
+  getApis(): Iterable<AnyApiFactory>;
 };