Provide 'throw' option for overrideExisting

docs/rtk-query/api/created-api/code-splitting.mdx

@@ -25,7 +25,14 @@ const injectEndpoints = (endpointOptions: InjectedEndpointOptions) =>
 
 interface InjectedEndpointOptions {
   endpoints: (build: EndpointBuilder) => NewEndpointDefinitions
-  overrideExisting?: boolean
+  /**
+   * Optionally allows endpoints to be overridden if defined by multiple `injectEndpoints` calls.
+   *
+   * If set to `true`, will override existing endpoints with the new definition.
+   * If set to `'throw'`, will throw an error if an endpoint is redefined with a different definition.
+   * If set to `false` (or unset), will not override existing endpoints with the new definition, and log a warning in development.
+   */
+  overrideExisting?: boolean | 'throw'
 }
 ```
 

docs/rtk-query/usage/code-splitting.mdx

@@ -56,5 +56,7 @@ export const { useExampleQuery } = extendedApi
 ```
 
 :::tip
-If you inject an endpoint that already exists and don't explicitly specify `overrideExisting: true`, the endpoint will not be overridden. In development mode, you will get a warning about this.
+If you inject an endpoint that already exists and don't explicitly specify `overrideExisting: true`, the endpoint
+will not be overridden. In development mode, you will get a warning about this if `overrideExisting` is set to `false`,
+and an error will be throw if set to `'throw'`.
 :::

packages/toolkit/src/query/apiTypes.ts

@@ -83,7 +83,14 @@ export type Api<
     endpoints: (
       build: EndpointBuilder<BaseQuery, TagTypes, ReducerPath>,
     ) => NewDefinitions
-    overrideExisting?: boolean
+    /**
+     * Optionally allows endpoints to be overridden if defined by multiple `injectEndpoints` calls.
+     *
+     * If set to `true`, will override existing endpoints with the new definition.
+     * If set to `'throw'`, will throw an error if an endpoint is redefined with a different definition.
+     * If set to `false` (or unset), will not override existing endpoints with the new definition, and log a warning in development.
+     */
+    overrideExisting?: boolean | 'throw'
   }): Api<
     BaseQuery,
     Definitions & NewDefinitions,

packages/toolkit/src/query/createApi.ts

@@ -353,16 +353,17 @@ export function buildCreateApi<Modules extends [Module<any>, ...Module<any>[]]>(
         evaluatedEndpoints,
       )) {
         if (
-          !inject.overrideExisting &&
+          inject.overrideExisting !== true &&
           endpointName in context.endpointDefinitions
         ) {
-          if (
+          const errorMessage = `called \`injectEndpoints\` to override already-existing endpointName ${endpointName} without specifying \`overrideExisting: true\``
+          if (inject.overrideExisting === 'throw') {
+            throw new Error(errorMessage)
+          } else if (
             typeof process !== 'undefined' &&
             process.env.NODE_ENV === 'development'
           ) {
-            console.error(
-              `called \`injectEndpoints\` to override already-existing endpointName ${endpointName} without specifying \`overrideExisting: true\``,
-            )
+            console.error(errorMessage)
           }
 
           continue

packages/toolkit/src/query/tests/injectEndpoints.test.tsx

@@ -0,0 +1,86 @@
+import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query'
+import { vi } from 'vitest'
+
+const api = createApi({
+  baseQuery: fetchBaseQuery({ baseUrl: 'https://example.com' }),
+  endpoints: () => ({}),
+})
+
+describe('injectEndpoints', () => {
+  test("query: overridding with `overrideEndpoints`='throw' throws an error", async () => {
+    const extended = api.injectEndpoints({
+      endpoints: (build) => ({
+        injected: build.query<unknown, string>({
+          query: () => '/success',
+        }),
+      }),
+    })
+
+    expect(() => {
+      extended.injectEndpoints({
+        overrideExisting: 'throw',
+        endpoints: (build) => ({
+          injected: build.query<unknown, string>({
+            query: () => '/success',
+          }),
+        }),
+      })
+    }).toThrowError(
+      new Error(
+        `called \`injectEndpoints\` to override already-existing endpointName injected without specifying \`overrideExisting: true\``,
+      ),
+    )
+  })
+
+  test('query: overridding an endpoint with `overrideEndpoints`=false does nothing in production', async () => {
+    const consoleMock = vi.spyOn(console, 'error').mockImplementation(() => {})
+
+    process.env.NODE_ENV = 'development'
+
+    const extended = api.injectEndpoints({
+      endpoints: (build) => ({
+        injected: build.query<unknown, string>({
+          query: () => '/success',
+        }),
+      }),
+    })
+
+    extended.injectEndpoints({
+      overrideExisting: false,
+      endpoints: (build) => ({
+        injected: build.query<unknown, string>({
+          query: () => '/success',
+        }),
+      }),
+    })
+
+    expect(consoleMock).toHaveBeenCalledWith(
+      `called \`injectEndpoints\` to override already-existing endpointName injected without specifying \`overrideExisting: true\``,
+    )
+  })
+
+  test('query: overridding with `overrideEndpoints`=false logs an error in development', async () => {
+    const consoleMock = vi.spyOn(console, 'error').mockImplementation(() => {})
+
+    process.env.NODE_ENV = 'production'
+
+    const extended = api.injectEndpoints({
+      endpoints: (build) => ({
+        injected: build.query<unknown, string>({
+          query: () => '/success',
+        }),
+      }),
+    })
+
+    extended.injectEndpoints({
+      overrideExisting: false,
+      endpoints: (build) => ({
+        injected: build.query<unknown, string>({
+          query: () => '/success',
+        }),
+      }),
+    })
+
+    expect(consoleMock).not.toHaveBeenCalled()
+  })
+})