fix: 404 and 500 route matching

.changeset/purple-swans-argue.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Improves matching of 404 and 500 routes

packages/astro/src/core/routing/match.ts

@@ -17,12 +17,23 @@ export function matchAllRoutes(pathname: string, manifest: ManifestData): RouteD
 	return manifest.routes.filter((route) => route.pattern.test(decodeURI(pathname)));
 }
 
+const ROUTE404_RE = /^\/404\/?$/;
+const ROUTE500_RE = /^\/500\/?$/;
+
+export function isRoute404(route: string) {
+	return ROUTE404_RE.test(route);
+}
+
+export function isRoute500(route: string) {
+	return ROUTE500_RE.test(route);
+}
+
 /**
  * Determines if the given route matches a 404 or 500 error page.
  *
  * @param {RouteData} route - The route data to check.
  * @returns {boolean} `true` if the route matches a 404 or 500 error page, otherwise `false`.
  */
 export function isRoute404or500(route: RouteData): boolean {
-	return route.pattern.test('/404') || route.pattern.test('/500');
+	return isRoute404(route.route) || isRoute500(route.route);
 }

packages/astro/src/i18n/index.ts

@@ -4,6 +4,7 @@ import { shouldAppendForwardSlash } from '../core/build/util.js';
 import { REROUTE_DIRECTIVE_HEADER } from '../core/constants.js';
 import { MissingLocale, i18nNoLocaleFoundInPath } from '../core/errors/errors-data.js';
 import { AstroError } from '../core/errors/index.js';
+import { isRoute404, isRoute500 } from '../core/routing/match.js';
 import type { AstroConfig, Locales, ValidRedirectStatus } from '../types/public/config.js';
 import type { APIContext } from '../types/public/context.js';
 import { createI18nMiddleware } from './middleware.js';
@@ -17,8 +18,9 @@ export function requestHasLocale(locales: Locales) {
 
 export function requestIs404Or500(request: Request, base = '') {
 	const url = new URL(request.url);
+	const pathname = url.pathname.slice(base.length);
 
-	return url.pathname.startsWith(`${base}/404`) || url.pathname.startsWith(`${base}/500`);
+	return isRoute404(pathname) || isRoute500(pathname);
 }
 
 // Checks if the pathname has any locale

packages/astro/src/vite-plugin-astro-server/route.ts

@@ -15,6 +15,7 @@ import { getProps } from '../core/render/index.js';
 import { createRequest } from '../core/request.js';
 import { redirectTemplate } from '../core/routing/3xx.js';
 import { matchAllRoutes } from '../core/routing/index.js';
+import { isRoute404, isRoute500 } from '../core/routing/match.js';
 import { PERSIST_SYMBOL } from '../core/session.js';
 import { getSortedPreloadedMatches } from '../prerender/routing.js';
 import type { ComponentInstance, ManifestData } from '../types/astro.js';
@@ -41,13 +42,11 @@ function isLoggedRequest(url: string) {
 }
 
 function getCustom404Route(manifestData: ManifestData): RouteData | undefined {
-	const route404 = /^\/404\/?$/;
-	return manifestData.routes.find((r) => route404.test(r.route));
+	return manifestData.routes.find((r) => isRoute404(r.route));
 }
 
 function getCustom500Route(manifestData: ManifestData): RouteData | undefined {
-	const route500 = /^\/500\/?$/;
-	return manifestData.routes.find((r) => route500.test(r.route));
+	return manifestData.routes.find((r) => isRoute500(r.route));
 }
 
 export async function matchRoute(