fix: Throw when prerendered routes have unresolvable content negotiation

.changeset/brown-ads-allow.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: precedence of `entries` should be `+page => +page.server => +server`

.changeset/polite-months-scream.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: prerendered routes will throw when exposing both a GET handler and a page, preventing impossible content negotiation

packages/kit/src/core/postbuild/analyse.js

@@ -21,10 +21,11 @@ export default forked(import.meta.url, analyse);
 /**
  * @param {{
  *   manifest_path: string;
+ *   manifest_data: import('types').ManifestData;
  *   env: Record<string, string>
  * }} opts
  */
-async function analyse({ manifest_path, env }) {
+async function analyse({ manifest_path, manifest_data, env }) {
 	/** @type {import('@sveltejs/kit').SSRManifest} */
 	const manifest = (await import(pathToFileURL(manifest_path).href)).manifest;
 
@@ -66,6 +67,10 @@ async function analyse({ manifest_path, env }) {
 
 	// analyse routes
 	for (const route of manifest._.routes) {
+		const route_data = /** @type {import('types').RouteData} */ (
+			manifest_data.routes.find((r) => r.id === route.id)
+		);
+
 		/** @type {Array<'GET' | 'POST'>} */
 		const page_methods = [];
 
@@ -86,7 +91,7 @@ async function analyse({ manifest_path, env }) {
 
 				if (mod.prerender && (mod.POST || mod.PATCH || mod.PUT || mod.DELETE)) {
 					throw new Error(
-						`Cannot prerender a +server file with POST, PATCH, PUT, or DELETE (${route.id})`
+						`Cannot prerender ${route_data.endpoint?.file} as it exposes POST, PATCH, PUT, or DELETE handlers`
 					);
 				}
 
@@ -128,10 +133,21 @@ async function analyse({ manifest_path, env }) {
 				validate_page_exports(page.universal, page.universal_id);
 			}
 
-			prerender = get_option(nodes, 'prerender') ?? false;
+			prerender = get_option(nodes, 'prerender') ?? prerender ?? false;
 
 			config = get_config(nodes);
-			entries ??= get_option(nodes, 'entries');
+			entries = get_option(nodes, 'entries') ?? entries;
+		}
+
+		if (prerender && route.endpoint && route.page) {
+			const page = /** @type {string} */ (
+				route_data.leaf?.component ?? route_data.leaf?.universal ?? route_data.leaf?.server
+			);
+			const endpoint = /** @type {string} */ (route_data.endpoint?.file);
+
+			throw new Error(
+				`Cannot prerender both ${page} and ${endpoint}. Disable prerendering for this route, or delete one of the files.`
+			);
 		}
 
 		metadata.routes.set(route.id, {

packages/kit/src/exports/vite/dev/index.js

@@ -146,6 +146,8 @@ export async function dev(vite, vite_config, svelte_config) {
 
 								return module.default;
 							};
+
+							result.component_id = node.component;
 						}
 
 						if (node.universal) {

packages/kit/src/exports/vite/index.js

@@ -687,6 +687,7 @@ function kit({ svelte_config }) {
 
 				const metadata = await analyse({
 					manifest_path,
+					manifest_data,
 					env: { ...env.private, ...env.public }
 				});
 

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

@@ -387,6 +387,25 @@ export async function respond(request, options, manifest, state) {
 				/** @type {Response} */
 				let response;
 
+				if (DEV && route.page && route.endpoint) {
+					const nodes = await Promise.all(
+						[...route.page.layouts, route.page.leaf].map((n) => {
+							if (n !== undefined) return manifest._.nodes[n]();
+						})
+					);
+
+					const mod = await route.endpoint();
+
+					if (get_option(nodes, 'prerender') ?? mod.prerender) {
+						const page = nodes.at(-1)?.component_id;
+						const endpoint = route.endpoint_id;
+
+						throw new Error(
+							`Cannot prerender both ${page} and ${endpoint}. Disable prerendering for this route, or delete one of the files.`
+						);
+					}
+				}
+
 				if (is_data_request) {
 					response = await render_data(
 						event,

packages/kit/src/types/internal.d.ts

@@ -323,6 +323,7 @@ export interface SSRNode {
 		entries?: PrerenderEntryGenerator;
 	};
 
+	component_id: string;
 	universal_id: string;
 	server_id: string;
 }

packages/kit/test/build-errors/apps/prerender-entry-generator-mismatch/package.json

@@ -1,5 +1,5 @@
 {
-	"name": "prerenderable-incorrect-fragment",
+	"name": "prerenderable-entry-generator-mismatch",
 	"private": true,
 	"version": "0.0.1",
 	"scripts": {

packages/kit/test/build-errors/apps/prerender-impossible-content-negotiation/package.json

@@ -0,0 +1,20 @@
+{
+	"name": "prerender-impossible-content-negotiation",
+	"private": true,
+	"version": "0.0.1",
+	"scripts": {
+		"dev": "vite dev",
+		"build": "vite build",
+		"preview": "vite preview",
+		"check": "svelte-kit sync && tsc && svelte-check"
+	},
+	"devDependencies": {
+		"@sveltejs/adapter-auto": "workspace:^",
+		"@sveltejs/kit": "workspace:^",
+		"svelte": "^3.56.0",
+		"svelte-check": "^3.0.2",
+		"typescript": "^4.9.4",
+		"vite": "^4.3.6"
+	},
+	"type": "module"
+}

packages/kit/test/build-errors/apps/prerender-impossible-content-negotiation/src/app.html

@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<html lang="en">
+	<head>
+		<meta charset="utf-8" />
+		<link rel="icon" href="%sveltekit.assets%/favicon.png" />
+		<meta name="viewport" content="width=device-width" />
+		%sveltekit.head%
+	</head>
+	<body>
+		<div>%sveltekit.body%</div>
+	</body>
+</html>

packages/kit/test/build-errors/apps/prerender-impossible-content-negotiation/src/routes/+page.svelte

@@ -0,0 +1 @@
+<h1>Hello world</h1>

packages/kit/test/build-errors/apps/prerender-impossible-content-negotiation/src/routes/+page.ts

@@ -0,0 +1 @@
+export const prerender = true;

packages/kit/test/build-errors/apps/prerender-impossible-content-negotiation/src/routes/+server.ts

@@ -0,0 +1 @@
+export function GET() {}

packages/kit/test/build-errors/apps/prerender-impossible-content-negotiation/svelte.config.js

@@ -0,0 +1,10 @@
+import adapter from '../../../../../adapter-auto/index.js';
+
+/** @type {import('@sveltejs/kit').Config} */
+const config = {
+	kit: {
+		adapter: adapter()
+	}
+};
+
+export default config;

packages/kit/test/build-errors/apps/prerender-impossible-content-negotiation/tsconfig.json

@@ -0,0 +1,15 @@
+{
+	"compilerOptions": {
+		"allowJs": true,
+		"checkJs": true,
+		"noEmit": true,
+		"module": "esnext",
+		"moduleResolution": "node",
+		"paths": {
+			"@sveltejs/kit": ["../../../../types"],
+			"$lib": ["./src/lib"],
+			"$lib/*": ["./src/lib/*"]
+		}
+	},
+	"extends": "./.svelte-kit/tsconfig.json"
+}

packages/kit/test/build-errors/apps/prerender-impossible-content-negotiation/vite.config.js

@@ -0,0 +1,23 @@
+import * as path from 'node:path';
+import { sveltekit } from '@sveltejs/kit/vite';
+
+/** @type {import('vite').UserConfig} */
+const config = {
+	build: {
+		minify: false
+	},
+
+	clearScreen: false,
+
+	logLevel: 'silent',
+
+	plugins: [sveltekit()],
+
+	server: {
+		fs: {
+			allow: [path.resolve('../../../../src')]
+		}
+	}
+};
+
+export default config;

packages/kit/test/build-errors/prerender.spec.js

@@ -26,3 +26,15 @@ test('entry generators should match their own route', () => {
 		`Error: The entries export from /[slug]/[notSpecific] generated entry /whatever/specific, which was matched by /[slug]/specific - see the \`handleEntryGeneratorMismatch\` option in https://kit.svelte.dev/docs/configuration#prerender for more info.${EOL}To suppress or handle this error, implement \`handleEntryGeneratorMismatch\` in https://kit.svelte.dev/docs/configuration#prerender`
 	);
 });
+
+test('prerendering a route with +page and +server files should fail due to impossible content negotiation', () => {
+	assert.throws(
+		() =>
+			execSync('pnpm build', {
+				cwd: path.join(process.cwd(), 'apps/prerender-impossible-content-negotiation'),
+				stdio: 'pipe',
+				timeout: 60000
+			}),
+		'Detected a prerendered route with both a +server and +page file (route: /). Because content negotiation for static files is impossible, this is not allowed.'
+	);
+});