discover backend feature factory

Co-authored-by: Patrik Oldsberg <poldsberg@gmail.com>
Signed-off-by: Vincenzo Scamporlino <vincenzos@spotify.com>

packages/backend-app-api/package.json

@@ -5,13 +5,26 @@
   "main": "src/index.ts",
   "types": "src/index.ts",
   "publishConfig": {
-    "access": "public",
-    "main": "dist/index.cjs.js",
-    "types": "dist/index.d.ts"
+    "access": "public"
   },
   "backstage": {
     "role": "node-library"
   },
+  "exports": {
+    ".": "./src/index.ts",
+    "./alpha": "./src/alpha.ts",
+    "./package.json": "./package.json"
+  },
+  "typesVersions": {
+    "*": {
+      "alpha": [
+        "src/alpha.ts"
+      ],
+      "package.json": [
+        "package.json"
+      ]
+    }
+  },
   "homepage": "https://backstage.io",
   "repository": {
     "type": "git",
@@ -36,6 +49,7 @@
     "@backstage/backend-plugin-api": "workspace:^",
     "@backstage/backend-tasks": "workspace:^",
     "@backstage/cli-common": "workspace:^",
+    "@backstage/cli-node": "workspace:^",
     "@backstage/config": "workspace:^",
     "@backstage/config-loader": "workspace:^",
     "@backstage/errors": "workspace:^",

packages/backend-app-api/src/alpha.ts

@@ -0,0 +1,118 @@
+/*
+ * 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 {
+  BackendFeature,
+  RootConfigService,
+  coreServices,
+  createServiceFactory,
+} from '@backstage/backend-plugin-api';
+import {
+  featureDiscoveryServiceRef,
+  FeatureDiscoveryService,
+} from '@backstage/backend-plugin-api/alpha';
+import { resolve as resolvePath, dirname } from 'path';
+import fs from 'fs-extra';
+import { BackstagePackageJson } from '@backstage/cli-node';
+
+const LOADED_PACKAGE_ROLES = ['backend-plugin', 'backend-module'];
+
+/** @internal */
+async function findClosestPackageDir(
+  searchDir: string,
+): Promise<string | undefined> {
+  let path = searchDir;
+
+  // Some confidence check to avoid infinite loop
+  for (let i = 0; i < 1000; i++) {
+    const packagePath = resolvePath(path, 'package.json');
+    const exists = await fs.pathExists(packagePath);
+    if (exists) {
+      return path;
+    }
+
+    const newPath = dirname(path);
+    if (newPath === path) {
+      return undefined;
+    }
+    path = newPath;
+  }
+
+  throw new Error(
+    `Iteration limit reached when searching for root package.json at ${searchDir}`,
+  );
+}
+
+/** @alpha */
+export class PackageDiscoveryService implements FeatureDiscoveryService {
+  constructor(private readonly config: RootConfigService) {}
+
+  async getBackendFeatures(): Promise<{ features: Array<BackendFeature> }> {
+    // if (this.config.getOptionalString('backend.packages') !== 'all') {
+    //   return { features: [] };
+    // }
+
+    console.log(`DEBUG: executing backend feature discovery`);
+    const packageDir = await findClosestPackageDir(process.argv[1]);
+    if (!packageDir) {
+      throw new Error('NOOOOOOOOOOOOOOOOOOOOOOOOOO');
+    }
+    console.log(`DEBUG: packageDir=`, packageDir);
+    const { dependencies } = require(resolvePath(packageDir, 'package.json'));
+    const dependencyNames = Object.keys(dependencies);
+    console.log(`DEBUG: dependencyNames=`, dependencyNames);
+
+    const features: BackendFeature[] = [];
+
+    for (const name of dependencyNames) {
+      const depPkg = require(`${name}/package.json`) as BackstagePackageJson;
+      if (!LOADED_PACKAGE_ROLES.includes(depPkg?.backstage?.role ?? '')) {
+        continue;
+      }
+      const depModule = require(name); // @backstage/plugin-catalog-backend
+      console.log(`DEBUG: loaded ${name} depModule=`, depModule);
+      Object.values(depModule).filter(exportValue => {
+        if (
+          exportValue &&
+          typeof exportValue === 'object' &&
+          (exportValue as any).$$type === '@backstage/BackendFeature'
+        ) {
+          features.push(exportValue as BackendFeature);
+        }
+        if (
+          typeof exportValue === 'function' &&
+          (exportValue as any).$$type === '@backstage/BackendFeatureFactory'
+        ) {
+          features.push(exportValue() as BackendFeature);
+        }
+      });
+    }
+
+    console.log(`DEBUG: features=`, features);
+    return { features };
+  }
+}
+
+/** @alpha */
+export const packageFeatureDiscoveryServiceFactory = createServiceFactory({
+  service: featureDiscoveryServiceRef,
+  deps: {
+    config: coreServices.rootConfig,
+  },
+  factory({ config }) {
+    return new PackageDiscoveryService(config);
+  },
+});