Add MethodResponse utility type

.changeset/hip-years-invite.md

@@ -0,0 +1,5 @@
+---
+"openapi-fetch": patch
+---
+
+Add MethodResponse utility type to easily get the return type of an endpoint on a client

packages/openapi-fetch/src/index.d.ts

@@ -190,6 +190,20 @@ export interface Client<Paths extends {}, Media extends MediaType = MediaType> {
   eject(...middleware: Middleware[]): void;
 }
 
+export type ClientPathsWithMethod<
+  CreatedClient extends Client<any, any>,
+  Method extends HttpMethod,
+> = CreatedClient extends Client<infer Paths, infer _Media> ? PathsWithMethod<Paths, Method> : never;
+
+export type MethodResponse<
+  CreatedClient extends Client<any, any>,
+  Method extends HttpMethod,
+  Path extends ClientPathsWithMethod<CreatedClient, Method>,
+  Options = {},
+> = CreatedClient extends Client<infer Paths extends { [key: string]: any }, infer Media extends MediaType>
+  ? NonNullable<FetchResponse<Paths[Path][Method], Options, Media>["data"]>
+  : never;
+
 export default function createClient<Paths extends {}, Media extends MediaType = MediaType>(
   clientOptions?: ClientOptions,
 ): Client<Paths, Media>;

packages/openapi-fetch/test/index.test.ts

@@ -1,6 +1,7 @@
 import { HttpResponse, type StrictResponse } from "msw";
 import { afterAll, beforeAll, describe, expect, expectTypeOf, it } from "vitest";
 import createClient, {
+  type MethodResponse,
   type Middleware,
   type MiddlewareCallbackParams,
   type QuerySerializerOptions,
@@ -132,6 +133,7 @@ describe("client", () => {
           created_at: number;
           updated_at: number;
         }>();
+        expectTypeOf(result.data).toEqualTypeOf<MethodResponse<typeof client, "get", "/mismatched-errors">>();
       } else {
         expectTypeOf(result.data).toBeUndefined();
         expectTypeOf(result.error).extract<{ code: number }>().toEqualTypeOf<{ code: number; message: string }>();