fix: post API routes in SSG should warn or error during dev mode

.changeset/famous-camels-study.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+add warning for post routes called when output is not server

packages/astro/src/core/endpoint/index.ts

@@ -41,7 +41,7 @@ export async function call(
 	}
 	const [params] = paramsAndPropsResp;
 
-	const response = await renderEndpoint(mod, opts.request, params);
+	const response = await renderEndpoint(mod, opts.request, params, opts.ssr);
 
 	if (response instanceof Response) {
 		return {

packages/astro/src/runtime/server/endpoint.ts

@@ -18,9 +18,19 @@ function getHandlerFromModule(mod: EndpointHandler, method: string) {
 }
 
 /** Renders an endpoint request to completion, returning the body. */
-export async function renderEndpoint(mod: EndpointHandler, request: Request, params: Params) {
+export async function renderEndpoint(
+	mod: EndpointHandler,
+	request: Request,
+	params: Params,
+	ssr?: boolean
+) {
 	const chosenMethod = request.method?.toLowerCase();
 	const handler = getHandlerFromModule(mod, chosenMethod);
+	if (!ssr && ssr === false && chosenMethod && chosenMethod !== 'get') {
+		// eslint-disable-next-line no-console
+		console.warn(`
+${chosenMethod} requests are not available when building a static site. Update your config to output: 'server' to handle ${chosenMethod} requests.`);
+	}
 	if (!handler || typeof handler !== 'function') {
 		// No handler found, so this should be a 404. Using a custom header
 		// to signal to the renderer that this is an internal 404 that should