Keep feature discovery and resolution logic separate

Signed-off-by: Eric Peterson <ericpeterson@spotify.com>

.changeset/mira-color-like.md

@@ -2,4 +2,4 @@
 '@backstage/frontend-defaults': patch
 ---
 
-Feature resolution logic used in `createApp` is now exposed via the `resolveFeatures` function.
+Feature discovery and resolution logic used in `createApp` is now exposed via the `getAvailableFeatures` and `resolveFeatures` functions respectively.

packages/frontend-defaults/report.api.md

@@ -45,6 +45,9 @@ export function createPublicSignInApp(options?: CreateAppOptions): {
   createRoot(): React_2.JSX.Element;
 };
 
+// @public (undocumented)
+export function getAvailableFeatures(config: Config): FrontendFeature[];
+
 // @public (undocumented)
 export function resolveFeatures(options: {
   config: Config;

packages/frontend-defaults/src/createApp.tsx

@@ -20,7 +20,6 @@ import { ConfigApi, coreExtensionData } from '@backstage/frontend-plugin-api';
 import { defaultConfigLoaderSync } from '../../core-app-api/src/app/defaultConfigLoader';
 // eslint-disable-next-line @backstage/no-relative-monorepo-imports
 import { overrideBaseUrlConfigs } from '../../core-app-api/src/app/overrideBaseUrlConfigs';
-import { resolveFeatures } from './discovery';
 import { ConfigReader } from '@backstage/config';
 import {
   CreateAppRouteBinder,
@@ -28,6 +27,9 @@ import {
   FrontendFeature,
   createSpecializedApp,
 } from '@backstage/frontend-app-api';
+import appPlugin from '@backstage/plugin-app';
+import { getAvailableFeatures } from './discovery';
+import { resolveFeatures } from './resolveFeatures';
 
 /**
  * A source of dynamically loaded frontend features.
@@ -87,12 +89,15 @@ export function createApp(options?: CreateAppOptions): {
         overrideBaseUrlConfigs(defaultConfigLoaderSync()),
       );
 
+    const discoveredFeatures = getAvailableFeatures(config);
+    const providedFeatures = await resolveFeatures({
+      config,
+      features: options?.features,
+    });
+
     const app = createSpecializedApp({
       config,
-      features: await resolveFeatures({
-        config,
-        features: options?.features,
-      }),
+      features: [appPlugin, ...discoveredFeatures, ...providedFeatures],
       bindRoutes: options?.bindRoutes,
       extensionFactoryMiddleware: options?.extensionFactoryMiddleware,
     });

packages/frontend-defaults/src/discovery.ts

@@ -15,10 +15,7 @@
  */
 
 import { Config, ConfigReader } from '@backstage/config';
-import { stringifyError } from '@backstage/errors';
 import { FrontendFeature } from '@backstage/frontend-app-api';
-import { CreateAppFeatureLoader } from './createApp';
-import appPlugin from '@backstage/plugin-app';
 
 interface DiscoveryGlobal {
   modules: Array<{ name: string; export?: string; default: unknown }>;
@@ -56,7 +53,7 @@ function readPackageDetectionConfig(config: Config) {
 }
 
 /**
- * @internal
+ * @public
  */
 export function getAvailableFeatures(config: Config): FrontendFeature[] {
   const discovered = (
@@ -97,29 +94,3 @@ function isBackstageFeature(obj: unknown): obj is FrontendFeature {
   }
   return false;
 }
-
-/** @public */
-export async function resolveFeatures(options: {
-  config: Config;
-  features?: (FrontendFeature | CreateAppFeatureLoader)[];
-}): Promise<FrontendFeature[]> {
-  const discoveredFeatures = getAvailableFeatures(options.config);
-  const features = [appPlugin, ...discoveredFeatures];
-  for (const entry of options.features ?? []) {
-    if ('load' in entry) {
-      try {
-        const result = await entry.load({ config: options.config });
-        features.push(...result.features);
-      } catch (e) {
-        throw new Error(
-          `Failed to read frontend features from loader '${entry.getLoaderName()}', ${stringifyError(
-            e,
-          )}`,
-        );
-      }
-    } else {
-      features.push(entry);
-    }
-  }
-  return features;
-}

packages/frontend-defaults/src/index.ts

@@ -26,4 +26,5 @@ export {
   type CreateAppFeatureLoader,
 } from './createApp';
 export { createPublicSignInApp } from './createPublicSignInApp';
-export { resolveFeatures } from './discovery';
+export { getAvailableFeatures } from './discovery';
+export { resolveFeatures } from './resolveFeatures';

packages/frontend-defaults/src/resolveFeatures.ts

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2025 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 { Config } from '@backstage/config';
+import { stringifyError } from '@backstage/errors';
+import { FrontendFeature } from '@backstage/frontend-app-api';
+import { CreateAppFeatureLoader } from './createApp';
+
+/** @public */
+export async function resolveFeatures(options: {
+  config: Config;
+  features?: (FrontendFeature | CreateAppFeatureLoader)[];
+}): Promise<FrontendFeature[]> {
+  const features = [];
+  for (const entry of options.features ?? []) {
+    if ('load' in entry) {
+      try {
+        const result = await entry.load({ config: options.config });
+        features.push(...result.features);
+      } catch (e) {
+        throw new Error(
+          `Failed to read frontend features from loader '${entry.getLoaderName()}', ${stringifyError(
+            e,
+          )}`,
+        );
+      }
+    } else {
+      features.push(entry);
+    }
+  }
+  return features;
+}