expose matched route

Author: Rich-Harris

packages/adapter-vercel/files/serverless.js

@@ -36,6 +36,12 @@ export default async (req, res) => {
 
 	const request = await getRequest({ base: `https://${req.headers.host}`, request: req });
 
+	const route_id = request.headers.get('x-sveltekit-matched-route');
+
+	if (route_id) {
+		res.setHeader('x-matched-route', route_id);
+	}
+
 	setResponse(
 		res,
 		await server.respond(request, {

packages/kit/src/runtime/server/respond.js

@@ -272,6 +272,7 @@ export async function respond(request, options, manifest, state) {
 				route = candidate;
 				event.route = { id: route.id };
 				event.params = decode_params(matched);
+				headers['x-sveltekit-matched-route'] = route.id;
 				break;
 			}
 		}