backend-defaults: Stop accepting callback BackendFeatures for backend.add

Co-authored-by: Camila Belo <camilaibs@gmail.com>
Signed-off-by: Johan Haals <johan.haals@gmail.com>

packages/backend-app-api/api-report.md

@@ -24,14 +24,6 @@ export interface Backend {
           default: BackendFeature;
         }>,
   ): void;
-  // @deprecated (undocumented)
-  add(
-    feature:
-      | (() => BackendFeature)
-      | Promise<{
-          default: () => BackendFeature;
-        }>,
-  ): void;
   // (undocumented)
   start(): Promise<void>;
   // (undocumented)

packages/backend-app-api/src/wiring/BackstageBackend.ts

@@ -25,12 +25,7 @@ export class BackstageBackend implements Backend {
     this.#initializer = new BackendInitializer(defaultServiceFactories);
   }
 
-  add(
-    feature:
-      | BackendFeature
-      | (() => BackendFeature)
-      | Promise<{ default: BackendFeature | (() => BackendFeature) }>,
-  ): void {
+  add(feature: BackendFeature | Promise<{ default: BackendFeature }>): void {
     if (isPromise(feature)) {
       this.#initializer.add(feature.then(f => unwrapFeature(f.default)));
     } else {
@@ -57,15 +52,8 @@ function isPromise<T>(value: unknown | Promise<T>): value is Promise<T> {
 }
 
 function unwrapFeature(
-  feature:
-    | BackendFeature
-    | (() => BackendFeature)
-    | { default: BackendFeature | (() => BackendFeature) },
+  feature: BackendFeature | { default: BackendFeature },
 ): BackendFeature {
-  if (typeof feature === 'function') {
-    return feature();
-  }
-
   if ('$$type' in feature) {
     return feature;
   }
@@ -75,10 +63,7 @@ function unwrapFeature(
   // when importing using a dynamic import.
   // TODO: This is a broader issue than just this piece of code, and should move away from CommonJS.
   if ('default' in feature) {
-    const defaultFeature = feature.default;
-    return typeof defaultFeature === 'function'
-      ? defaultFeature()
-      : defaultFeature;
+    return feature.default;
   }
 
   return feature;

packages/backend-app-api/src/wiring/types.ts

@@ -26,18 +26,6 @@ import {
  */
 export interface Backend {
   add(feature: BackendFeature | Promise<{ default: BackendFeature }>): void;
-  /**
-   * @deprecated The ability to add features defined as a callback is being
-   * removed. Please update the installed feature to no longer be defined as a
-   * callback, typically this means updating it to use the latest version of
-   * `@backstage/backend-plugin-api`. If the feature is from a third-party
-   * package, please reach out to the package maintainer to update it.
-   */
-  add(
-    feature:
-      | (() => BackendFeature)
-      | Promise<{ default: () => BackendFeature }>,
-  ): void;
   start(): Promise<void>;
   stop(): Promise<void>;
 }