Move ExtensionFactoryMiddleware from frontend-plugin-api to frontend-app-api

The `ExtensionFactoryMiddleware` type is only used by the app-level wiring
and has been moved to `@backstage/frontend-app-api` as its canonical location.

The type is preserved in `@backstage/frontend-plugin-api` with a `@deprecated`
tag pointing to the new location. All internal usages have been updated to
import from the new location.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

.changeset/move-extension-factory-middleware-app-api.md

@@ -0,0 +1,5 @@
+---
+'@backstage/frontend-app-api': patch
+---
+
+Added the `ExtensionFactoryMiddleware` type as a public export.

.changeset/move-extension-factory-middleware-plugin-api.md

@@ -0,0 +1,5 @@
+---
+'@backstage/frontend-plugin-api': patch
+---
+
+Deprecated the `ExtensionFactoryMiddleware` type, which has been moved to `@backstage/frontend-app-api`.

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

@@ -4,10 +4,13 @@
 
 ```ts
 import { ApiHolder } from '@backstage/core-plugin-api';
+import { ApiHolder as ApiHolder_2 } from '@backstage/frontend-plugin-api';
 import { AppNode } from '@backstage/frontend-plugin-api';
 import { AppTree } from '@backstage/frontend-plugin-api';
 import { ConfigApi } from '@backstage/core-plugin-api';
-import { ExtensionFactoryMiddleware } from '@backstage/frontend-plugin-api';
+import { ExtensionDataContainer } from '@backstage/frontend-plugin-api';
+import { ExtensionDataRef } from '@backstage/frontend-plugin-api';
+import { ExtensionDataValue } from '@backstage/frontend-plugin-api';
 import { ExternalRouteRef } from '@backstage/frontend-plugin-api';
 import { FrontendFeature } from '@backstage/frontend-plugin-api';
 import { FrontendPlugin } from '@backstage/frontend-plugin-api';
@@ -177,6 +180,18 @@ export type CreateSpecializedAppOptions = {
   };
 };
 
+// @public (undocumented)
+export type ExtensionFactoryMiddleware = (
+  originalFactory: (contextOverrides?: {
+    config?: JsonObject;
+  }) => ExtensionDataContainer<ExtensionDataRef>,
+  context: {
+    node: AppNode;
+    apis: ApiHolder_2;
+    config?: JsonObject;
+  },
+) => Iterable<ExtensionDataValue<any, any>>;
+
 // @public
 export type FrontendPluginInfoResolver = (ctx: {
   packageJson(): Promise<JsonObject | undefined>;

packages/frontend-app-api/src/tree/instantiateAppNodeTree.test.ts

@@ -19,7 +19,6 @@ import {
   Extension,
   ExtensionDataRef,
   ExtensionDefinition,
-  ExtensionFactoryMiddleware,
   ExtensionInput,
   PortableSchema,
   ResolvedExtensionInput,
@@ -29,6 +28,7 @@ import {
   createExtensionInput,
   createFrontendPlugin,
 } from '@backstage/frontend-plugin-api';
+import { ExtensionFactoryMiddleware } from '../wiring/types';
 import {
   createAppNodeInstance,
   instantiateAppNodeTree,

packages/frontend-app-api/src/tree/instantiateAppNodeTree.ts

@@ -18,10 +18,10 @@ import {
   ApiHolder,
   ExtensionDataContainer,
   ExtensionDataRef,
-  ExtensionFactoryMiddleware,
   ExtensionInput,
   ResolvedExtensionInputs,
 } from '@backstage/frontend-plugin-api';
+import { ExtensionFactoryMiddleware } from '../wiring/types';
 import mapValues from 'lodash/mapValues';
 import { AppNode, AppNodeInstance } from '@backstage/frontend-plugin-api';
 // eslint-disable-next-line @backstage/no-relative-monorepo-imports

packages/frontend-app-api/src/wiring/createSpecializedApp.tsx

@@ -29,9 +29,9 @@ import {
   createApiFactory,
   routeResolutionApiRef,
   AppNode,
-  ExtensionFactoryMiddleware,
   FrontendFeature,
 } from '@backstage/frontend-plugin-api';
+import { ExtensionFactoryMiddleware } from './types';
 import {
   AnyApiFactory,
   ApiHolder,

packages/frontend-app-api/src/wiring/index.ts

@@ -20,3 +20,4 @@ export {
 } from './createSpecializedApp';
 export { type FrontendPluginInfoResolver } from './createPluginInfoAttacher';
 export { type AppError, type AppErrorTypes } from './createErrorCollector';
+export { type ExtensionFactoryMiddleware } from './types';

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

@@ -0,0 +1,36 @@
+/*
+ * 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 { JsonObject } from '@backstage/types';
+import {
+  ApiHolder,
+  AppNode,
+  ExtensionDataContainer,
+  ExtensionDataRef,
+  ExtensionDataValue,
+} from '@backstage/frontend-plugin-api';
+
+/** @public */
+export type ExtensionFactoryMiddleware = (
+  originalFactory: (contextOverrides?: {
+    config?: JsonObject;
+  }) => ExtensionDataContainer<ExtensionDataRef>,
+  context: {
+    node: AppNode;
+    apis: ApiHolder;
+    config?: JsonObject;
+  },
+) => Iterable<ExtensionDataValue<any, any>>;

packages/frontend-defaults/report.api.md

@@ -8,7 +8,7 @@ import { AppErrorTypes } from '@backstage/frontend-app-api';
 import { Config } from '@backstage/config';
 import { ConfigApi } from '@backstage/frontend-plugin-api';
 import { CreateAppRouteBinder } from '@backstage/frontend-app-api';
-import { ExtensionFactoryMiddleware } from '@backstage/frontend-plugin-api';
+import { ExtensionFactoryMiddleware } from '@backstage/frontend-app-api';
 import { FrontendFeature } from '@backstage/frontend-plugin-api';
 import { FrontendFeatureLoader } from '@backstage/frontend-plugin-api';
 import { FrontendPluginInfoResolver } from '@backstage/frontend-app-api';

packages/frontend-defaults/src/createApp.tsx

@@ -18,7 +18,6 @@ import { JSX, lazy, ReactNode, Suspense } from 'react';
 import {
   ConfigApi,
   coreExtensionData,
-  ExtensionFactoryMiddleware,
   FrontendFeature,
   FrontendFeatureLoader,
 } from '@backstage/frontend-plugin-api';
@@ -31,6 +30,7 @@ import { ConfigReader } from '@backstage/config';
 import {
   CreateAppRouteBinder,
   createSpecializedApp,
+  ExtensionFactoryMiddleware,
   FrontendPluginInfoResolver,
 } from '@backstage/frontend-app-api';
 import appPlugin from '@backstage/plugin-app';

packages/frontend-plugin-api/report.api.md

@@ -3,17 +3,13 @@
 > Do not edit this file. It is a report generated by [API Extractor](https://api-extractor.com/).
 
 ```ts
-import { AnyRouteRefParams as AnyRouteRefParams_2 } from '@backstage/frontend-plugin-api';
-import { ApiRef as ApiRef_2 } from '@backstage/frontend-plugin-api';
+import { ApiRef as ApiRef_2 } from '@backstage/core-plugin-api';
 import { ComponentType } from 'react';
 import type { Config } from '@backstage/config';
-import { ConfigurableExtensionDataRef as ConfigurableExtensionDataRef_2 } from '@backstage/frontend-plugin-api';
 import { Expand } from '@backstage/types';
 import { ExpandRecursive } from '@backstage/types';
 import { ExtensionBlueprint as ExtensionBlueprint_2 } from '@backstage/frontend-plugin-api';
-import { ExtensionBlueprintParams as ExtensionBlueprintParams_2 } from '@backstage/frontend-plugin-api';
 import { ExtensionDataRef as ExtensionDataRef_2 } from '@backstage/frontend-plugin-api';
-import { ExtensionInput as ExtensionInput_2 } from '@backstage/frontend-plugin-api';
 import { JsonObject } from '@backstage/types';
 import { JsonValue } from '@backstage/types';
 import { JSX as JSX_2 } from 'react';
@@ -21,7 +17,6 @@ import { JSX as JSX_3 } from 'react/jsx-runtime';
 import { Observable } from '@backstage/types';
 import { PropsWithChildren } from 'react';
 import { ReactNode } from 'react';
-import { SwappableComponentRef as SwappableComponentRef_2 } from '@backstage/frontend-plugin-api';
 import type { z } from 'zod';
 
 // @public
@@ -82,12 +77,12 @@ export type AnalyticsImplementation = {
 };
 
 // @public
-export const AnalyticsImplementationBlueprint: ExtensionBlueprint_2<{
+export const AnalyticsImplementationBlueprint: ExtensionBlueprint<{
   kind: 'analytics';
   params: <TDeps extends { [name in string]: unknown }>(
     params: AnalyticsImplementationFactory<TDeps>,
-  ) => ExtensionBlueprintParams_2<AnalyticsImplementationFactory<{}>>;
-  output: ExtensionDataRef_2<
+  ) => ExtensionBlueprintParams<AnalyticsImplementationFactory<{}>>;
+  output: ExtensionDataRef<
     AnalyticsImplementationFactory<{}>,
     'core.analytics.factory',
     {}
@@ -96,7 +91,7 @@ export const AnalyticsImplementationBlueprint: ExtensionBlueprint_2<{
   config: {};
   configInput: {};
   dataRefs: {
-    factory: ConfigurableExtensionDataRef_2<
+    factory: ConfigurableExtensionDataRef<
       AnalyticsImplementationFactory<{}>,
       'core.analytics.factory',
       {}
@@ -149,7 +144,7 @@ export type AnyRouteRefParams =
   | undefined;
 
 // @public
-export const ApiBlueprint: ExtensionBlueprint_2<{
+export const ApiBlueprint: ExtensionBlueprint<{
   kind: 'api';
   params: <
     TApi,
@@ -157,13 +152,13 @@ export const ApiBlueprint: ExtensionBlueprint_2<{
     TDeps extends { [name in string]: unknown },
   >(
     params: ApiFactory<TApi, TImpl, TDeps>,
-  ) => ExtensionBlueprintParams_2<AnyApiFactory>;
-  output: ExtensionDataRef_2<AnyApiFactory, 'core.api.factory', {}>;
+  ) => ExtensionBlueprintParams<AnyApiFactory>;
+  output: ExtensionDataRef<AnyApiFactory, 'core.api.factory', {}>;
   inputs: {};
   config: {};
   configInput: {};
   dataRefs: {
-    factory: ConfigurableExtensionDataRef_2<
+    factory: ConfigurableExtensionDataRef<
       AnyApiFactory,
       'core.api.factory',
       {}
@@ -388,16 +383,16 @@ export interface ConfigurableExtensionDataRef<
 
 // @public (undocumented)
 export const coreExtensionData: {
-  title: ConfigurableExtensionDataRef_2<string, 'core.title', {}>;
-  icon: ConfigurableExtensionDataRef_2<IconElement, 'core.icon', {}>;
-  reactElement: ConfigurableExtensionDataRef_2<
+  title: ConfigurableExtensionDataRef<string, 'core.title', {}>;
+  icon: ConfigurableExtensionDataRef<IconElement, 'core.icon', {}>;
+  reactElement: ConfigurableExtensionDataRef<
     JSX_2.Element,
     'core.reactElement',
     {}
   >;
-  routePath: ConfigurableExtensionDataRef_2<string, 'core.routing.path', {}>;
-  routeRef: ConfigurableExtensionDataRef_2<
-    RouteRef<AnyRouteRefParams_2>,
+  routePath: ConfigurableExtensionDataRef<string, 'core.routing.path', {}>;
+  routeRef: ConfigurableExtensionDataRef<
+    RouteRef<AnyRouteRefParams>,
     'core.routing.ref',
     {}
   >;
@@ -909,7 +904,7 @@ export const errorApiRef: ApiRef<ErrorApi>;
 // @public (undocumented)
 export const ErrorDisplay: {
   (props: ErrorDisplayProps): JSX.Element | null;
-  ref: SwappableComponentRef_2<ErrorDisplayProps, ErrorDisplayProps>;
+  ref: SwappableComponentRef<ErrorDisplayProps, ErrorDisplayProps>;
 };
 
 // @public (undocumented)
@@ -956,7 +951,7 @@ export interface ExtensionBlueprint<
   // (undocumented)
   make<
     TName extends string | undefined,
-    TParamsInput extends AnyParamsInput_2<NonNullable<T['params']>>,
+    TParamsInput extends AnyParamsInput<NonNullable<T['params']>>,
     UParentInputs extends ExtensionDataRef,
   >(args: {
     name?: TName;
@@ -1011,7 +1006,7 @@ export interface ExtensionBlueprint<
     };
     factory(
       originalFactory: <
-        TParamsInput extends AnyParamsInput_2<NonNullable<T['params']>>,
+        TParamsInput extends AnyParamsInput<NonNullable<T['params']>>,
       >(
         params: TParamsInput extends ExtensionBlueprintDefineParams
           ? TParamsInput
@@ -1226,7 +1221,7 @@ export type ExtensionDefinitionParameters = {
   params?: object | ExtensionBlueprintDefineParams;
 };
 
-// @public (undocumented)
+// @public @deprecated (undocumented)
 export type ExtensionFactoryMiddleware = (
   originalFactory: (contextOverrides?: {
     config?: JsonObject;
@@ -1471,14 +1466,14 @@ export const microsoftAuthApiRef: ApiRef<
 >;
 
 // @public
-export const NavItemBlueprint: ExtensionBlueprint_2<{
+export const NavItemBlueprint: ExtensionBlueprint<{
   kind: 'nav-item';
   params: {
     title: string;
     icon: IconComponent;
     routeRef: RouteRef<undefined>;
   };
-  output: ExtensionDataRef_2<
+  output: ExtensionDataRef<
     {
       title: string;
       icon: IconComponent;
@@ -1491,7 +1486,7 @@ export const NavItemBlueprint: ExtensionBlueprint_2<{
   config: {};
   configInput: {};
   dataRefs: {
-    target: ConfigurableExtensionDataRef_2<
+    target: ConfigurableExtensionDataRef<
       {
         title: string;
         icon: IconComponent;
@@ -1506,7 +1501,7 @@ export const NavItemBlueprint: ExtensionBlueprint_2<{
 // @public (undocumented)
 export const NotFoundErrorPage: {
   (props: NotFoundErrorPageProps): JSX.Element | null;
-  ref: SwappableComponentRef_2<NotFoundErrorPageProps, NotFoundErrorPageProps>;
+  ref: SwappableComponentRef<NotFoundErrorPageProps, NotFoundErrorPageProps>;
 };
 
 // @public (undocumented)
@@ -1594,7 +1589,7 @@ export interface OverridableExtensionDefinition<
     TExtraInputs extends {
       [inputName in string]: ExtensionInput;
     },
-    TParamsInput extends AnyParamsInput<NonNullable<T['params']>>,
+    TParamsInput extends AnyParamsInput_2<NonNullable<T['params']>>,
     UParentInputs extends ExtensionDataRef,
   >(
     args: Expand<
@@ -1620,7 +1615,7 @@ export interface OverridableExtensionDefinition<
         };
         factory?(
           originalFactory: <
-            TFactoryParamsReturn extends AnyParamsInput<
+            TFactoryParamsReturn extends AnyParamsInput_2<
               NonNullable<T['params']>
             >,
           >(
@@ -1719,7 +1714,7 @@ export interface OverridableFrontendPlugin<
 }
 
 // @public
-export const PageBlueprint: ExtensionBlueprint_2<{
+export const PageBlueprint: ExtensionBlueprint<{
   kind: 'page';
   params: {
     defaultPath?: [Error: `Use the 'path' param instead`];
@@ -1731,23 +1726,23 @@ export const PageBlueprint: ExtensionBlueprint_2<{
     noHeader?: boolean;
   };
   output:
-    | ExtensionDataRef_2<string, 'core.routing.path', {}>
-    | ExtensionDataRef_2<
-        RouteRef<AnyRouteRefParams_2>,
+    | ExtensionDataRef<string, 'core.routing.path', {}>
+    | ExtensionDataRef<
+        RouteRef<AnyRouteRefParams>,
         'core.routing.ref',
         {
           optional: true;
         }
       >
-    | ExtensionDataRef_2<JSX_2.Element, 'core.reactElement', {}>
-    | ExtensionDataRef_2<
+    | ExtensionDataRef<JSX_2.Element, 'core.reactElement', {}>
+    | ExtensionDataRef<
         string,
         'core.title',
         {
           optional: true;
         }
       >
-    | ExtensionDataRef_2<
+    | ExtensionDataRef<
         IconElement,
         'core.icon',
         {
@@ -1755,24 +1750,24 @@ export const PageBlueprint: ExtensionBlueprint_2<{
         }
       >;
   inputs: {
-    pages: ExtensionInput_2<
-      | ConfigurableExtensionDataRef_2<JSX_2.Element, 'core.reactElement', {}>
-      | ConfigurableExtensionDataRef_2<string, 'core.routing.path', {}>
-      | ConfigurableExtensionDataRef_2<
-          RouteRef<AnyRouteRefParams_2>,
+    pages: ExtensionInput<
+      | ConfigurableExtensionDataRef<JSX_2.Element, 'core.reactElement', {}>
+      | ConfigurableExtensionDataRef<string, 'core.routing.path', {}>
+      | ConfigurableExtensionDataRef<
+          RouteRef<AnyRouteRefParams>,
           'core.routing.ref',
           {
             optional: true;
           }
         >
-      | ConfigurableExtensionDataRef_2<
+      | ConfigurableExtensionDataRef<
           string,
           'core.title',
           {
             optional: true;
           }
         >
-      | ConfigurableExtensionDataRef_2<
+      | ConfigurableExtensionDataRef<
           IconElement,
           'core.icon',
           {
@@ -1800,7 +1795,7 @@ export const PageBlueprint: ExtensionBlueprint_2<{
 // @public
 export const PageLayout: {
   (props: PageLayoutProps): JSX.Element | null;
-  ref: SwappableComponentRef_2<PageLayoutProps, PageLayoutProps>;
+  ref: SwappableComponentRef<PageLayoutProps, PageLayoutProps>;
 };
 
 // @public
@@ -1839,14 +1834,14 @@ export type PendingOAuthRequest = {
 };
 
 // @public
-export const PluginHeaderActionBlueprint: ExtensionBlueprint_2<{
+export const PluginHeaderActionBlueprint: ExtensionBlueprint<{
   kind: 'plugin-header-action';
   params: (params: {
     loader: () => Promise<JSX.Element>;
-  }) => ExtensionBlueprintParams_2<{
+  }) => ExtensionBlueprintParams<{
     loader: () => Promise<JSX.Element>;
   }>;
-  output: ExtensionDataRef_2<JSX_2, 'core.reactElement', {}>;
+  output: ExtensionDataRef<JSX_2, 'core.reactElement', {}>;
   inputs: {};
   config: {};
   configInput: {};
@@ -1909,7 +1904,7 @@ export type ProfileInfoApi = {
 // @public (undocumented)
 export const Progress: {
   (props: ProgressProps): JSX.Element | null;
-  ref: SwappableComponentRef_2<ProgressProps, ProgressProps>;
+  ref: SwappableComponentRef<ProgressProps, ProgressProps>;
 };
 
 // @public (undocumented)
@@ -2020,7 +2015,7 @@ export type StorageValueSnapshot<TValue extends JsonValue> =
     };
 
 // @public
-export const SubPageBlueprint: ExtensionBlueprint_2<{
+export const SubPageBlueprint: ExtensionBlueprint<{
   kind: 'sub-page';
   params: {
     path: string;
@@ -2030,17 +2025,17 @@ export const SubPageBlueprint: ExtensionBlueprint_2<{
     routeRef?: RouteRef;
   };
   output:
-    | ExtensionDataRef_2<string, 'core.routing.path', {}>
-    | ExtensionDataRef_2<
-        RouteRef<AnyRouteRefParams_2>,
+    | ExtensionDataRef<string, 'core.routing.path', {}>
+    | ExtensionDataRef<
+        RouteRef<AnyRouteRefParams>,
         'core.routing.ref',
         {
           optional: true;
         }
       >
-    | ExtensionDataRef_2<JSX_2, 'core.reactElement', {}>
-    | ExtensionDataRef_2<string, 'core.title', {}>
-    | ExtensionDataRef_2<
+    | ExtensionDataRef<JSX_2, 'core.reactElement', {}>
+    | ExtensionDataRef<string, 'core.title', {}>
+    | ExtensionDataRef<
         IconElement,
         'core.icon',
         {

packages/frontend-plugin-api/src/wiring/types.ts

@@ -60,7 +60,10 @@ export type ExtensionDataContainer<UExtensionData extends ExtensionDataRef> =
       : never;
   };
 
-/** @public */
+/**
+ * @public
+ * @deprecated Moved to {@link @backstage/frontend-app-api#ExtensionFactoryMiddleware}
+ */
 export type ExtensionFactoryMiddleware = (
   originalFactory: (contextOverrides?: {
     config?: JsonObject;