core-api: migrate app context to use a separate type and implementation

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

@@ -64,6 +64,7 @@ import { AppThemeProvider } from './AppThemeProvider';
 import {
   AppComponents,
   AppConfigLoader,
+  AppContext,
   AppOptions,
   AppRouteBinder,
   BackstageApp,
@@ -139,6 +140,38 @@ function useConfigLoader(
   return { api: configReader };
 }
 
+class AppContextImpl implements AppContext {
+  constructor(private readonly app: PrivateAppImpl) {}
+
+  getPlugins(): BackstagePlugin<any, any>[] {
+    // eslint-disable-next-line no-console
+    console.warn('appContext.getPlugins() is deprecated and will be removed');
+    return this.app.getPlugins();
+  }
+
+  getSystemIcon(key: string): IconComponent {
+    return this.app.getSystemIcon(key);
+  }
+
+  getProvider(): React.ComponentType<{}> {
+    // eslint-disable-next-line no-console
+    console.warn('appContext.getProvider() is deprecated and will be removed');
+    return this.app.getProvider();
+  }
+
+  getRouter(): React.ComponentType<{}> {
+    // eslint-disable-next-line no-console
+    console.warn('appContext.getRouter() is deprecated and will be removed');
+    return this.app.getRouter();
+  }
+
+  getRoutes(): JSX.Element[] {
+    // eslint-disable-next-line no-console
+    console.warn('appContext.getRoutes() is deprecated and will be removed');
+    return this.app.getRoutes();
+  }
+}
+
 export class PrivateAppImpl implements BackstageApp {
   private apiHolder?: ApiHolder;
   private configApi?: ConfigApi;
@@ -236,6 +269,8 @@ export class PrivateAppImpl implements BackstageApp {
   }
 
   getProvider(): ComponentType<{}> {
+    const appContext = new AppContextImpl(this);
+
     const Provider = ({ children }: PropsWithChildren<{}>) => {
       const appThemeApi = useMemo(
         () => AppThemeSelector.createWithStorage(this.themes),
@@ -273,7 +308,7 @@ export class PrivateAppImpl implements BackstageApp {
 
       return (
         <ApiProvider apis={this.getApiHolder()}>
-          <AppContextProvider app={this}>
+          <AppContextProvider appContext={appContext}>
             <AppThemeProvider>
               <RoutingProvider
                 routePaths={routePaths}

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

@@ -15,25 +15,25 @@
  */
 
 import React, { createContext, PropsWithChildren, useContext } from 'react';
-import { BackstageApp } from './types';
+import { AppContext } from './types';
 
-const Context = createContext<BackstageApp | undefined>(undefined);
+const Context = createContext<AppContext | undefined>(undefined);
 
 type Props = {
-  app: BackstageApp;
+  appContext: AppContext;
 };
 
 export const AppContextProvider = ({
-  app,
+  appContext,
   children,
 }: PropsWithChildren<Props>) => (
-  <Context.Provider value={app} children={children} />
+  <Context.Provider value={appContext} children={children} />
 );
 
-export const useApp = (): BackstageApp => {
-  const app = useContext(Context);
-  if (!app) {
+export const useApp = (): AppContext => {
+  const appContext = useContext(Context);
+  if (!appContext) {
     throw new Error('No app context available');
   }
-  return app;
+  return appContext;
 };

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

@@ -190,3 +190,30 @@ export type BackstageApp = {
    */
   getRoutes(): JSX.Element[];
 };
+
+export type AppContext = {
+  /**
+   * @deprecated Will be removed
+   */
+  getPlugins(): BackstagePlugin<any, any>[];
+
+  /**
+   * Get a common or custom icon for this app.
+   */
+  getSystemIcon(key: IconKey): IconComponent;
+
+  /**
+   * @deprecated Will be removed
+   */
+  getProvider(): ComponentType<{}>;
+
+  /**
+   * @deprecated Will be removed
+   */
+  getRouter(): ComponentType<{}>;
+
+  /**
+   * @deprecated Will be removed
+   */
+  getRoutes(): JSX.Element[];
+};