fix(prerendering): never prerender custom 500 routes

.changeset/wet-snakes-act.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+fixed an edge case where attempting to prerender a 500 route led to missing styles and scripts

packages/astro/src/vite-plugin-scanner/index.ts

@@ -3,7 +3,7 @@ import type { AstroSettings } from '../@types/astro.js';
 import { type LogOptions } from '../core/logger/core.js';
 
 import { bold } from 'kleur/colors';
-import { extname } from 'node:path';
+import { basename, extname } from 'node:path';
 import { normalizePath } from 'vite';
 import { warn } from '../core/logger/core.js';
 import { isEndpoint, isPage, rootRelativePath } from '../core/util.js';
@@ -15,6 +15,14 @@ export interface AstroPluginScannerOptions {
 	logging: LogOptions;
 }
 
+function isPrerenderEligible(id: string) {
+	const base = basename(id)
+	// astro core doesn't use a prerendered 404.astro
+	// but netlify adapter achieves the effect by using redirects
+	// so it would still be a regression to consider it ineligible
+	return /* !base.startsWith("404") && */ !base.startsWith("500")
+}
+
 const KNOWN_FILE_EXTENSIONS = ['.astro', '.js', '.ts'];
 
 export default function astroScannerPlugin({
@@ -46,6 +54,11 @@ export default function astroScannerPlugin({
 			if (typeof pageOptions.prerender === 'undefined') {
 				pageOptions.prerender = defaultPrerender;
 			}
+
+			if (!isPrerenderEligible(id)) {
+				pageOptions.prerender = false;
+			}
+
 			// `getStaticPaths` warning is just a string check, should be good enough for most cases
 			if (
 				!pageOptions.prerender &&

packages/astro/test/fixtures/ssr-prerender/src/external-stylesheet.css

@@ -0,0 +1,3 @@
+body {
+    background-color: ivory;
+}

packages/astro/test/fixtures/ssr-prerender/src/pages/500.astro

@@ -0,0 +1,6 @@
+
+---
+import "../external-stylesheet.css"
+export const prerender = true
+---
+<h1>{new Date(Date.now()).toISOString()}</h1>

packages/astro/test/fixtures/ssr-prerender/src/pages/fivehundred.astro

@@ -0,0 +1,4 @@
+---
+return new Response(null, { status: 500 })
+---
+<p>This html will not be served</p>

packages/astro/test/ssr-prerender.test.js

@@ -30,8 +30,25 @@ describe('SSR: prerender', () => {
 			const app = await fixture.loadTestAdapterApp();
 			/** @type {Set<string>} */
 			const assets = app.manifest.assets;
-			expect(assets.size).to.equal(1);
-			expect(Array.from(assets)[0].endsWith('static/index.html')).to.be.true;
+			expect(assets).to.contain('/static/index.html');
+		});
+
+		// remove when support for prerendered 404 and 500 routes is added
+		it('ignores prerender = true for 500 routes', async () => {
+			const app = await fixture.loadTestAdapterApp();
+			const fiveHundredRoute = app.manifest.routes.find(route => route.routeData.route === '/500');
+			expect(fiveHundredRoute.routeData.prerender).to.equal(false);
+		});
+
+		it('includes expected styles in a redirected 500 route that has `prerender = true`', async () => {
+			const app = await fixture.loadTestAdapterApp();
+			const request = new Request('http://example.com/fivehundred');
+			const response = await app.render(request);
+			const html = await response.text();
+			const $ = cheerio.load(html);
+
+			// length will be 0 if the stylesheet does not get included
+			expect($('link[rel=stylesheet]')).to.have.a.lengthOf(1);
 		});
 	});