home: add support for new backend system

Signed-off-by: Vincenzo Scamporlino <vincenzos@spotify.com>

plugins/home/alpha-api-report.md

@@ -0,0 +1,13 @@
+## API Report File for "@backstage/plugin-home"
+
+> Do not edit this file. It is a report generated by [API Extractor](https://api-extractor.com/).
+
+```ts
+import { BackstagePlugin } from '@backstage/frontend-plugin-api';
+
+// @alpha (undocumented)
+const _default: BackstagePlugin;
+export default _default;
+
+// (No @packageDocumentation comment for this package)
+```

plugins/home/package.json

@@ -23,6 +23,21 @@
     "backstage",
     "homepage"
   ],
+  "exports": {
+    ".": "./src/index.ts",
+    "./alpha": "./src/alpha.tsx",
+    "./package.json": "./package.json"
+  },
+  "typesVersions": {
+    "*": {
+      "alpha": [
+        "src/alpha.tsx"
+      ],
+      "package.json": [
+        "package.json"
+      ]
+    }
+  },
   "sideEffects": false,
   "scripts": {
     "build": "backstage-cli package build",
@@ -39,6 +54,7 @@
     "@backstage/core-app-api": "workspace:^",
     "@backstage/core-components": "workspace:^",
     "@backstage/core-plugin-api": "workspace:^",
+    "@backstage/frontend-plugin-api": "workspace:^",
     "@backstage/plugin-catalog-react": "workspace:^",
     "@backstage/plugin-home-react": "workspace:^",
     "@backstage/theme": "workspace:^",

plugins/home/src/alpha.tsx

@@ -0,0 +1,53 @@
+/*
+ * 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 React from 'react';
+
+import { rootRouteRef } from './routes';
+import {
+  coreExtensionData,
+  createExtensionInput,
+  createPageExtension,
+  createPlugin,
+} from '@backstage/frontend-plugin-api';
+
+const HomepageCompositionRootExtension = createPageExtension({
+  id: 'home',
+  defaultPath: '/home',
+  routeRef: rootRouteRef,
+  inputs: {
+    props: createExtensionInput(
+      { children: coreExtensionData.reactElement.optional() },
+      // TODO(vinzscam): title
+      {
+        singleton: true,
+        optional: true,
+      },
+    ),
+  },
+  loader: ({ inputs }) =>
+    import('./components/').then(m => (
+      <m.HomepageCompositionRoot children={inputs.props?.children} />
+    )),
+});
+
+/**
+ * @alpha
+ */
+export default createPlugin({
+  id: 'home',
+  extensions: [HomepageCompositionRootExtension],
+});