fix: action not found should return 404 (#11278)

When posting to a form action, that does exist, the server returned
500. With this fix, it will return 404 error "not found"

.changeset/warm-sloths-cry.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: correctly return 404 when a form action is not found

packages/kit/src/runtime/server/page/actions.js

@@ -216,7 +216,7 @@ async function call_action(event, actions) {
 
 	const action = actions[name];
 	if (!action) {
-		throw new Error(`No action with name '${name}' found`);
+		throw error(404, `No action with name '${name}' found`);
 	}
 
 	if (!is_form_content_type(event.request)) {

packages/kit/test/apps/basics/test/test.js

@@ -1260,6 +1260,24 @@ test.describe('Actions', () => {
 		expect(error.message).toBe('Actions expect form-encoded data (received application/json)');
 		expect(response.status()).toBe(415);
 	});
+
+	test('submitting to a form action that does not exists, should return http status code 404', async ({
+		baseURL,
+		page
+	}) => {
+		const randomActionName = 'some-random-action';
+		const response = await page.request.fetch(`${baseURL}/actions/enhance?/${randomActionName}`, {
+			method: 'POST',
+			body: 'irrelevant',
+			headers: {
+				Origin: `${baseURL}`
+			}
+		});
+		const { type, error } = await response.json();
+		expect(type).toBe('error');
+		expect(error.message).toBe(`No action with name '${randomActionName}' found`);
+		expect(response.status()).toBe(404);
+	});
 });
 
 // Run in serial to not pollute the log with (correct) cookie warnings