Merge pull request #21632 from davidfestal/support-additional-config-schemas

Support external config schemas in the backend

plugins/app-node/api-report.md

@@ -3,9 +3,23 @@
 > Do not edit this file. It is a report generated by [API Extractor](https://api-extractor.com/).
 
 ```ts
+import { ConfigSchema } from '@backstage/config-loader';
 import { ExtensionPoint } from '@backstage/backend-plugin-api';
 import { Handler } from 'express';
 
+// @public
+export interface ConfigSchemaExtensionPoint {
+  setConfigSchema(configSchema: ConfigSchema): void;
+}
+
+// @public
+export const configSchemaExtensionPoint: ExtensionPoint<ConfigSchemaExtensionPoint>;
+
+// @public
+export function loadCompiledConfigSchema(
+  appDistDir: string,
+): Promise<ConfigSchema | undefined>;
+
 // @public
 export interface StaticFallbackHandlerExtensionPoint {
   setStaticFallbackHandler(handler: Handler): void;

plugins/app-node/package.json

@@ -34,7 +34,9 @@
   ],
   "dependencies": {
     "@backstage/backend-plugin-api": "workspace:^",
+    "@backstage/config-loader": "workspace:^",
     "@types/express": "^4.17.6",
-    "express": "^4.17.1"
+    "express": "^4.17.1",
+    "fs-extra": "10.1.0"
   }
 }

plugins/app-node/src/extensions.ts

@@ -15,6 +15,7 @@
  */
 
 import { createExtensionPoint } from '@backstage/backend-plugin-api';
+import { ConfigSchema } from '@backstage/config-loader';
 import { Handler } from 'express';
 
 /**
@@ -50,3 +51,25 @@ export const staticFallbackHandlerExtensionPoint =
   createExtensionPoint<StaticFallbackHandlerExtensionPoint>({
     id: 'app.staticFallbackHandler',
   });
+
+/**
+ * The interface for {@link configSchemaExtensionPoint}.
+ *
+ * @public
+ */
+export interface ConfigSchemaExtensionPoint {
+  /**
+   * Sets the config schema. This can only be done once.
+   */
+  setConfigSchema(configSchema: ConfigSchema): void;
+}
+
+/**
+ * An extension point the exposes the ability to override the config schema used by the frontend application.
+ *
+ * @public
+ */
+export const configSchemaExtensionPoint =
+  createExtensionPoint<ConfigSchemaExtensionPoint>({
+    id: 'app.configSchema',
+  });

plugins/app-node/src/index.ts

@@ -23,4 +23,8 @@
 export {
   staticFallbackHandlerExtensionPoint,
   type StaticFallbackHandlerExtensionPoint,
+  configSchemaExtensionPoint,
+  type ConfigSchemaExtensionPoint,
 } from './extensions';
+
+export { loadCompiledConfigSchema } from './schema';

plugins/app-node/src/schema.ts

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2024 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 fs from 'fs-extra';
+import { resolve as resolvePath } from 'path';
+import { ConfigSchema, loadConfigSchema } from '@backstage/config-loader';
+
+/**
+ * Loads the config schema that is embedded in the frontend build.
+ *
+ * @public
+ */
+export async function loadCompiledConfigSchema(
+  appDistDir: string,
+): Promise<ConfigSchema | undefined> {
+  const schemaPath = resolvePath(appDistDir, '.config-schema.json');
+  if (await fs.pathExists(schemaPath)) {
+    const serializedSchema = await fs.readJson(schemaPath);
+
+    return await loadConfigSchema({
+      serialized: serializedSchema,
+    });
+  }
+
+  return undefined;
+}