From 36a40b4903059537a8e0ef174819c44ef2b886a7 Mon Sep 17 00:00:00 2001
From: Vincenzo Scamporlino <vincenzos@spotify.com>
Date: Tue, 1 Aug 2023 20:43:28 +0200
Subject: [PATCH] define BackendFeatureFactory

Signed-off-by: Vincenzo Scamporlino <vincenzos@spotify.com>
---
 packages/backend-app-api/src/alpha.ts         | 48 ++++++++++++-------
 .../src/wiring/factories.ts                   | 17 ++++---
 .../backend-plugin-api/src/wiring/index.ts    |  1 +
 .../backend-plugin-api/src/wiring/types.ts    |  8 ++++
 4 files changed, 51 insertions(+), 23 deletions(-)

diff --git a/packages/backend-app-api/src/alpha.ts b/packages/backend-app-api/src/alpha.ts
index da77c7cfc5..31b61950b9 100644
--- a/packages/backend-app-api/src/alpha.ts
+++ b/packages/backend-app-api/src/alpha.ts
@@ -16,6 +16,7 @@
 
 import {
   BackendFeature,
+  BackendFeatureFactory,
   RootConfigService,
   coreServices,
   createServiceFactory,
@@ -71,8 +72,11 @@ export class PackageDiscoveryService implements FeatureDiscoveryService {
       throw new Error('NOOOOOOOOOOOOOOOOOOOOOOOOOO');
     }
     console.log(`DEBUG: packageDir=`, packageDir);
-    const { dependencies } = require(resolvePath(packageDir, 'package.json'));
-    const dependencyNames = Object.keys(dependencies);
+    const { dependencies } = require(resolvePath(
+      packageDir,
+      'package.json',
+    )) as BackstagePackageJson;
+    const dependencyNames = Object.keys(dependencies || {});
     console.log(`DEBUG: dependencyNames=`, dependencyNames);
 
     const features: BackendFeature[] = [];
@@ -82,23 +86,16 @@ export class PackageDiscoveryService implements FeatureDiscoveryService {
       if (!LOADED_PACKAGE_ROLES.includes(depPkg?.backstage?.role ?? '')) {
         continue;
       }
-      const depModule = require(name); // @backstage/plugin-catalog-backend
+      const depModule = require(name);
       console.log(`DEBUG: loaded ${name} depModule=`, depModule);
-      Object.values(depModule).filter(exportValue => {
-        if (
-          exportValue &&
-          typeof exportValue === 'object' &&
-          (exportValue as any).$$type === '@backstage/BackendFeature'
-        ) {
-          features.push(exportValue as BackendFeature);
+      for (const exportValue of Object.values(depModule)) {
+        if (isBackendFeature(exportValue)) {
+          features.push(exportValue);
         }
-        if (
-          typeof exportValue === 'function' &&
-          (exportValue as any).$$type === '@backstage/BackendFeatureFactory'
-        ) {
-          features.push(exportValue() as BackendFeature);
+        if (isBackendFeatureFactory(exportValue)) {
+          features.push(exportValue());
         }
-      });
+      }
     }
 
     console.log(`DEBUG: features=`, features);
@@ -116,3 +113,22 @@ export const packageFeatureDiscoveryServiceFactory = createServiceFactory({
     return new PackageDiscoveryService(config);
   },
 });
+
+function isBackendFeature(value: unknown): value is BackendFeature {
+  return (
+    !!value &&
+    typeof value === 'object' &&
+    (value as BackendFeature).$$type === '@backstage/BackendFeature'
+  );
+}
+
+function isBackendFeatureFactory(
+  value: unknown,
+): value is BackendFeatureFactory {
+  return (
+    !!value &&
+    typeof value === 'object' &&
+    (value as BackendFeatureFactory).$$type ===
+      '@backstage/BackendFeatureFactory'
+  );
+}
diff --git a/packages/backend-plugin-api/src/wiring/factories.ts b/packages/backend-plugin-api/src/wiring/factories.ts
index 41584e9a29..ba9238e0e0 100644
--- a/packages/backend-plugin-api/src/wiring/factories.ts
+++ b/packages/backend-plugin-api/src/wiring/factories.ts
@@ -17,11 +17,10 @@
 import {
   BackendModuleRegistrationPoints,
   BackendPluginRegistrationPoints,
-  BackendFeature,
   ExtensionPoint,
-  InternalBackendFeature,
   InternalBackendModuleRegistration,
   InternalBackendPluginRegistration,
+  BackendFeatureFactory,
 } from './types';
 
 /**
@@ -92,9 +91,10 @@ export const catalogPlugin = createBackendPlugin({
  */
 export function createBackendPlugin<TOptions extends [options?: object] = []>(
   config: BackendPluginConfig | ((...params: TOptions) => BackendPluginConfig),
-): (...params: TOptions) => BackendFeature {
+): BackendFeatureFactory<TOptions> {
   const configCallback = typeof config === 'function' ? config : () => config;
-  const factory = (...options: TOptions): InternalBackendFeature => {
+
+  const factory: BackendFeatureFactory<TOptions> = (...options) => {
     const c = configCallback(...options);
 
     let registrations: InternalBackendPluginRegistration[];
@@ -149,8 +149,8 @@ export function createBackendPlugin<TOptions extends [options?: object] = []>(
       },
     };
   };
-
   factory.$$type = '@backstage/BackendFeatureFactory';
+
   return factory;
 }
 
@@ -184,9 +184,9 @@ export interface BackendModuleConfig {
  */
 export function createBackendModule<TOptions extends [options?: object] = []>(
   config: BackendModuleConfig | ((...params: TOptions) => BackendModuleConfig),
-): (...params: TOptions) => BackendFeature {
+): BackendFeatureFactory<TOptions> {
   const configCallback = typeof config === 'function' ? config : () => config;
-  return (...options: TOptions): InternalBackendFeature => {
+  const factory: BackendFeatureFactory<TOptions> = (...options: TOptions) => {
     const c = configCallback(...options);
 
     let registrations: InternalBackendModuleRegistration[];
@@ -231,4 +231,7 @@ export function createBackendModule<TOptions extends [options?: object] = []>(
       },
     };
   };
+  factory.$$type = '@backstage/BackendFeatureFactory';
+
+  return factory;
 }
diff --git a/packages/backend-plugin-api/src/wiring/index.ts b/packages/backend-plugin-api/src/wiring/index.ts
index 9cb767b8ac..0b7104374a 100644
--- a/packages/backend-plugin-api/src/wiring/index.ts
+++ b/packages/backend-plugin-api/src/wiring/index.ts
@@ -28,5 +28,6 @@ export type {
   BackendModuleRegistrationPoints,
   BackendPluginRegistrationPoints,
   BackendFeature,
+  BackendFeatureFactory,
   ExtensionPoint,
 } from './types';
diff --git a/packages/backend-plugin-api/src/wiring/types.ts b/packages/backend-plugin-api/src/wiring/types.ts
index c81ee3ceb7..b9b4f3ff10 100644
--- a/packages/backend-plugin-api/src/wiring/types.ts
+++ b/packages/backend-plugin-api/src/wiring/types.ts
@@ -67,6 +67,14 @@ export interface BackendModuleRegistrationPoints {
   }): void;
 }
 
+/** @public */
+export interface BackendFeatureFactory<
+  TOptions extends [options?: object] = [],
+> {
+  (...options: TOptions): BackendFeature;
+  $$type: '@backstage/BackendFeatureFactory';
+}
+
 /** @public */
 export interface BackendFeature {
   // NOTE: This type is opaque in order to simplify future API evolution.