fix(client): require explicit methods for non-GET requests

docs/guide/typed-fetch.md

@@ -35,6 +35,8 @@ The client constrains every part of the request:
 - **Body, query, params:** when your handler uses [`defineHandler.withValidator()`](./server-routing.md#validation), validator schemas become the input types and the client enforces them at the call site.
 - **Response type:** the return type matches what your handler returns after [JSON serialization](./type-safety.md#serialization).
 
+Omitting `method` sends GET. For a route without a GET handler, specify a supported method, such as `{ method: 'POST' }`.
+
 ## Query Parameters
 
 Pass `query` for GET requests with search parameters:

docs/reference/api/client.md

@@ -43,6 +43,8 @@ function fetch<P extends keyof RouteMap, M extends MethodsOf<P>>(
 | `retry`   | `number`                 | Number of retry attempts (ofetch default: 1 for GET).      |
 | `timeout` | `number`                 | Request timeout in milliseconds.                           |
 
+Omitting `method` sends GET. Non-GET calls require an explicit `method`, including calls that specify the method as a generic type argument.
+
 Returns the parsed JSON response body, or `undefined` for 204 responses. Throws `FetchError` on non-2xx responses.
 
 ## `FetchError` {#fetcherror}

packages/void/src/runtime/fetch.ts

@@ -5,7 +5,7 @@ export { FetchError };
 
 import type { RouteMap } from 'void/routes';
 export type MethodsOf<P extends keyof RouteMap> = keyof RouteMap[P] & string;
-type DefaultMethod<P extends keyof RouteMap> = 'GET' extends MethodsOf<P> ? 'GET' : never;
+type DefaultMethod<P extends keyof RouteMap> = 'GET' extends MethodsOf<P> ? 'GET' : MethodsOf<P>;
 
 type RouteEntry<P extends keyof RouteMap, M extends MethodsOf<P>> = RouteMap[P][M] extends {
   input: infer I;
@@ -47,7 +47,7 @@ type FetchOptions<P extends keyof RouteMap, M extends MethodsOf<P>> = BodyOption
     baseURL?: string;
     retry?: number;
     timeout?: number;
-  };
+  } & ('GET' extends M ? unknown : { method: M });
 
 export type UntypedFetchOptions = {
   method?: string;
@@ -77,7 +77,11 @@ const browserFetch = createRouteFetch((...args) => globalThis.fetch(...args));
  * ```
  */
 export function fetch<P extends keyof RouteMap & string>(
-  path: HasRequiredInput<P, DefaultMethod<P>> extends false ? P : never,
+  path: 'GET' extends MethodsOf<P>
+    ? HasRequiredInput<P, DefaultMethod<P>> extends false
+      ? P
+      : never
+    : never,
 ): Promise<OutputOf<P, DefaultMethod<P>>>;
 export function fetch<P extends keyof RouteMap & string, M extends MethodsOf<P> = DefaultMethod<P>>(
   path: P,

packages/void/test/unit/fetch.typecheck.ts

@@ -1,7 +1,34 @@
 import { describe, it } from 'vite-plus/test';
 import { fetch as typedFetch } from '../../src/runtime/fetch.ts';
 
+declare module 'void/routes' {
+  interface RouteMap {
+    '/api/rebuild': {
+      POST: { input: {}; output: { started: boolean } };
+    };
+  }
+}
+
 describe('typed fetch client', () => {
+  it('type: requires an explicit method whenever the request cannot default to GET', () => {
+    const _check = async () => {
+      const result = await typedFetch('/api/rebuild', { method: 'POST' });
+      const started: boolean = result.started;
+      void started;
+      await typedFetch('/api/hello', {});
+
+      // @ts-expect-error - a POST-only route cannot be called with the default GET
+      await typedFetch('/api/rebuild');
+      // @ts-expect-error - an options object does not supply a runtime method
+      await typedFetch('/api/rebuild', {});
+      // @ts-expect-error - generic type arguments do not set the runtime method
+      await typedFetch<'/api/rebuild', 'POST'>('/api/rebuild', {});
+      // @ts-expect-error - selecting POST requires a method even when GET also exists
+      await typedFetch<'/api/users', 'POST'>('/api/users', { body: { name: 'Alice' } });
+    };
+    void _check;
+  });
+
   it('type: output is correctly narrowed per route', () => {
     const _check = async () => {
       const hello = await typedFetch('/api/hello');