fix: use vercel routing utils

.changeset/tidy-walls-check.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/vercel': patch
+---
+
+Fixes a bug that caused redirect loops when trailingSlash was set

packages/vercel/package.json

@@ -40,6 +40,7 @@
     "@vercel/analytics": "^1.4.1",
     "@vercel/edge": "^1.2.1",
     "@vercel/nft": "^0.29.0",
+    "@vercel/routing-utils": "^5.0.0",
     "esbuild": "^0.24.0",
     "fast-glob": "^3.3.3"
   },

packages/vercel/src/index.ts

@@ -2,6 +2,7 @@ import { cpSync, existsSync, mkdirSync, readFileSync } from 'node:fs';
 import { basename } from 'node:path';
 import { pathToFileURL } from 'node:url';
 import { emptyDir, removeDir, writeJson } from '@astrojs/internal-helpers/fs';
+import { type Route, getTransformedRoutes, normalizeRoutes } from '@vercel/routing-utils';
 import type {
 	AstroAdapter,
 	AstroConfig,
@@ -25,6 +26,7 @@ import {
 	getInjectableWebAnalyticsContent,
 } from './lib/web-analytics.js';
 import { generateEdgeMiddleware } from './serverless/middleware.js';
+import { AstroError } from 'astro/errors';
 
 const PACKAGE_NAME = '@astrojs/vercel';
 
@@ -261,16 +263,23 @@ export default function vercelAdapter({
 						);
 					}
 					const vercelConfigPath = new URL('vercel.json', config.root);
-					if (existsSync(vercelConfigPath)) {
+					if (
+						config.trailingSlash &&
+						config.trailingSlash !== 'ignore' &&
+						existsSync(vercelConfigPath)
+					) {
 						try {
 							const vercelConfig = JSON.parse(readFileSync(vercelConfigPath, 'utf-8'));
-							if (vercelConfig.trailingSlash === true && config.trailingSlash === 'always') {
-								logger.warn(
-									'\n' +
-										`\tYour "vercel.json" \`trailingSlash\` configuration (set to \`true\`) will conflict with your Astro \`trailinglSlash\` configuration (set to \`"always"\`).\n` +
-										// biome-ignore lint/style/noUnusedTemplateLiteral: <explanation>
-										`\tThis would cause infinite redirects under certain conditions and throw an \`ERR_TOO_MANY_REDIRECTS\` error.\n` +
-										`\tTo prevent this, change your Astro configuration and update \`"trailingSlash"\` to \`"ignore"\`.\n`
+							if (
+								(vercelConfig.trailingSlash === true && config.trailingSlash === 'never') ||
+								(vercelConfig.trailingSlash === false && config.trailingSlash === 'always')
+							) {
+								logger.error(
+									`
+	Your "vercel.json" \`trailingSlash\` configuration (set to \`${vercelConfig.trailingSlash}\`) will conflict with your Astro \`trailingSlash\` configuration (set to \`${JSON.stringify(config.trailingSlash)}\`).
+	This would cause infinite redirects or duplicate content issues. 
+	Please remove the \`trailingSlash\` configuration from your \`vercel.json\` file or Astro config.
+`
 								);
 							}
 						} catch (_err) {
@@ -435,14 +444,12 @@ export default function vercelAdapter({
 				}
 				const fourOhFourRoute = routes.find((route) => route.pathname === '/404');
 				const destination = new URL('./.vercel/output/config.json', _config.root);
-				const finalRoutes = [
-					...getRedirects(routes, _config),
+				const finalRoutes: Route[] = [
 					{
 						src: `^/${_config.build.assets}/(.*)$`,
 						headers: { 'cache-control': 'public, max-age=31536000, immutable' },
 						continue: true,
 					},
-					{ handle: 'filesystem' },
 				];
 				if (_buildOutput === 'server') {
 					finalRoutes.push(...routeDefinitions);
@@ -467,6 +474,30 @@ export default function vercelAdapter({
 						});
 					}
 				}
+				// The Vercel `trailingSlash` option
+				let trailingSlash: boolean | undefined;
+				// Vercel's `trailingSlash` option maps to Astro's like so:
+				// - `true` -> `"always"`
+				// - `false` -> `"never"`
+				// - `undefined` -> `"ignore"`
+				// If config is set to "ignore", we leave it as undefined.
+				if (_config.trailingSlash && _config.trailingSlash !== 'ignore') {
+					// Otherwise, map it accordingly.
+					trailingSlash = _config.trailingSlash === 'always';
+				}
+
+				const { routes: redirects = [], error } = getTransformedRoutes({
+					trailingSlash,
+					rewrites: [],
+					redirects: getRedirects(routes, _config),
+					headers: [],
+				});
+				if (error) {
+					throw new AstroError(
+						`Error generating redirects: ${error.message}`,
+						error.link ? `${error.action ?? 'More info'}: ${error.link}` : undefined
+					);
+				}
 
 				let images: VercelImageConfig | undefined;
 				if (imageService || imagesConfig) {
@@ -487,11 +518,21 @@ export default function vercelAdapter({
 					}
 				}
 
+				const normalized = normalizeRoutes([...(redirects ?? []), ...finalRoutes]);
+				if (normalized.error) {
+					throw new AstroError(
+						`Error generating routes: ${normalized.error.message}`,
+						normalized.error.link
+							? `${normalized.error.action ?? 'More info'}: ${normalized.error.link}`
+							: undefined
+					);
+				}
+
 				// Output configuration
 				// https://vercel.com/docs/build-output-api/v3#build-output-configuration
 				await writeJson(destination, {
 					version: 3,
-					routes: finalRoutes,
+					routes: normalized.routes,
 					images,
 				});
 

packages/vercel/src/lib/redirects.ts

@@ -1,7 +1,9 @@
 import nodePath from 'node:path';
-import { appendForwardSlash, removeLeadingForwardSlash } from '@astrojs/internal-helpers/path';
+import { removeLeadingForwardSlash } from '@astrojs/internal-helpers/path';
 import type { AstroConfig, IntegrationResolvedRoute, RoutePart } from 'astro';
 
+import type { Redirect } from '@vercel/routing-utils';
+
 const pathJoin = nodePath.posix.join;
 
 // https://vercel.com/docs/project-configuration#legacy/routes
@@ -40,10 +42,32 @@ function getParts(part: string, file: string) {
 
 	return result;
 }
+/**
+ * Convert Astro routes into Vercel path-to-regexp syntax, which are the input for getTransformedRoutes
+ */
+function getMatchPattern(segments: RoutePart[][]) {
+	return segments
+		.map((segment) => {
+			return segment
+				.map((part) => {
+					if (part.spread) {
+						// Extract parameter name from spread syntax (e.g., "...slug" -> "slug")
+						const paramName = part.content.startsWith('...') ? part.content.slice(3) : part.content;
+						return `:${paramName}*`;
+					}
+					if (part.dynamic) {
+						return `:${part.content}`;
+					}
+					return part.content;
+				})
+				.join('');
+		})
+		.join('/');
+}
 
 // Copied from /home/juanm04/dev/misc/astro/packages/astro/src/core/routing/manifest/create.ts
 // 2022-04-26
-function getMatchPattern(segments: RoutePart[][]) {
+function getMatchRegex(segments: RoutePart[][]) {
 	return segments
 		.map((segment, segmentIndex) => {
 			return segment.length === 1 && segment[0].spread
@@ -72,37 +96,16 @@ function getMatchPattern(segments: RoutePart[][]) {
 		.join('');
 }
 
-function getReplacePattern(segments: RoutePart[][]) {
-	let n = 0;
-	let result = '';
-
-	for (const segment of segments) {
-		for (const part of segment) {
-			// biome-ignore lint/style/useTemplate: <explanation>
-			if (part.dynamic) result += '$' + ++n;
-			else result += part.content;
-		}
-		result += '/';
-	}
-
-	// Remove trailing slash
-	result = result.slice(0, -1);
-
-	return result;
-}
-
 function getRedirectLocation(route: IntegrationResolvedRoute, config: AstroConfig): string {
 	if (route.redirectRoute) {
-		const pattern = getReplacePattern(route.redirectRoute.segments);
-		const path = config.trailingSlash === 'always' ? appendForwardSlash(pattern) : pattern;
-		return pathJoin(config.base, path);
-		// biome-ignore lint/style/noUselessElse: <explanation>
-	} else if (typeof route.redirect === 'object') {
+		const pattern = getMatchPattern(route.redirectRoute.segments);
+		return pathJoin(config.base, pattern);
+	}
+
+	if (typeof route.redirect === 'object') {
 		return pathJoin(config.base, route.redirect.destination);
-		// biome-ignore lint/style/noUselessElse: <explanation>
-	} else {
-		return pathJoin(config.base, route.redirect || '');
 	}
+	return pathJoin(config.base, route.redirect || '');
 }
 
 function getRedirectStatus(route: IntegrationResolvedRoute): number {
@@ -119,40 +122,20 @@ export function escapeRegex(content: string) {
 		.map((s: string) => {
 			return getParts(s, content);
 		});
-	return `^/${getMatchPattern(segments)}$`;
+	return `^/${getMatchRegex(segments)}$`;
 }
 
-export function getRedirects(
-	routes: IntegrationResolvedRoute[],
-	config: AstroConfig
-): VercelRoute[] {
-	const redirects: VercelRoute[] = [];
+export function getRedirects(routes: IntegrationResolvedRoute[], config: AstroConfig): Redirect[] {
+	const redirects: Redirect[] = [];
 
 	for (const route of routes) {
 		if (route.type === 'redirect') {
 			redirects.push({
-				src: config.base + getMatchPattern(route.segments),
-				headers: { Location: getRedirectLocation(route, config) },
-				status: getRedirectStatus(route),
+				source: config.base + getMatchPattern(route.segments),
+				destination: getRedirectLocation(route, config),
+				statusCode: getRedirectStatus(route),
 			});
-		} else if (route.type === 'page' && route.pattern !== '/') {
-			if (config.trailingSlash === 'always') {
-				redirects.push({
-					src: config.base + getMatchPattern(route.segments),
-					// biome-ignore lint/style/useTemplate: <explanation>
-					headers: { Location: config.base + getReplacePattern(route.segments) + '/' },
-					status: 308,
-				});
-			} else if (config.trailingSlash === 'never') {
-				redirects.push({
-					// biome-ignore lint/style/useTemplate: <explanation>
-					src: config.base + getMatchPattern(route.segments) + '/',
-					headers: { Location: config.base + getReplacePattern(route.segments) },
-					status: 308,
-				});
-			}
 		}
 	}
-
 	return redirects;
 }

packages/vercel/test/isr.test.js

@@ -38,31 +38,31 @@ describe('ISR', () => {
 				dest: '_render',
 			},
 			{
-				src: '^/excluded(?:\\/(.*?))?$',
+				src: '^/excluded(?:/(.*?))?$',
 				dest: '_render',
 			},
 			{
-				src: '^\\/_server-islands\\/([^/]+?)\\/?$',
+				src: '^/_server-islands/([^/]+?)/?$',
 				dest: '_render',
 			},
 			{
-				src: '^\\/_image\\/?$',
+				src: '^/_image/?$',
 				dest: '_render',
 			},
 			{
-				src: '^\\/excluded\\/([^/]+?)\\/?$',
+				src: '^/excluded/([^/]+?)/?$',
 				dest: '/_isr?x_astro_path=$0',
 			},
 			{
-				src: '^\\/excluded(?:\\/(.*?))?\\/?$',
+				src: '^/excluded(?:/(.*?))?/?$',
 				dest: '/_isr?x_astro_path=$0',
 			},
 			{
-				src: '^\\/one\\/?$',
+				src: '^/one/?$',
 				dest: '/_isr?x_astro_path=$0',
 			},
 			{
-				src: '^\\/two\\/?$',
+				src: '^/two/?$',
 				dest: '/_isr?x_astro_path=$0',
 			},
 		]);

packages/vercel/test/prerendered-error-pages.test.js

@@ -18,7 +18,7 @@ describe('prerendered error pages routing', () => {
 		assert.deepEqual(
 			deploymentConfig.routes.find((r) => r.status === 404),
 			{
-				src: '/.*',
+				src: '^/.*$',
 				dest: '/404.html',
 				status: 404,
 			}

packages/vercel/test/redirects.test.js

@@ -27,30 +27,28 @@ describe('Redirects', () => {
 	async function getConfig() {
 		const json = await fixture.readFile('../.vercel/output/config.json');
 		const config = JSON.parse(json);
-
 		return config;
 	}
 
 	it('define static routes', async () => {
 		const config = await getConfig();
-
-		const oneRoute = config.routes.find((r) => r.src === '/one');
+		const oneRoute = config.routes.find((r) => r.src === '^/one$');
 		assert.equal(oneRoute.headers.Location, '/');
 		assert.equal(oneRoute.status, 301);
 
-		const twoRoute = config.routes.find((r) => r.src === '/two');
+		const twoRoute = config.routes.find((r) => r.src === '^/two$');
 		assert.equal(twoRoute.headers.Location, '/');
 		assert.equal(twoRoute.status, 301);
 
-		const threeRoute = config.routes.find((r) => r.src === '/three');
+		const threeRoute = config.routes.find((r) => r.src === '^/three$');
 		assert.equal(threeRoute.headers.Location, '/');
 		assert.equal(threeRoute.status, 302);
 	});
 
 	it('define redirects for static files', async () => {
 		const config = await getConfig();
 
-		const staticRoute = config.routes.find((r) => r.src === '/Basic/http-2-0.html');
+		const staticRoute = config.routes.find((r) => r.src === '^/Basic/http-2-0\\.html$');
 		assert.notEqual(staticRoute, undefined);
 		assert.equal(staticRoute.headers.Location, '/posts/http2');
 		assert.equal(staticRoute.status, 301);
@@ -59,25 +57,24 @@ describe('Redirects', () => {
 	it('defines dynamic routes', async () => {
 		const config = await getConfig();
 
-		const blogRoute = config.routes.find((r) => r.src.startsWith('/blog'));
+		const blogRoute = config.routes.find((r) => r.src.startsWith('^/blog'));
 		assert.notEqual(blogRoute, undefined);
 		assert.equal(blogRoute.headers.Location.startsWith('/team/articles'), true);
 		assert.equal(blogRoute.status, 301);
 	});
 
-	it('define trailingSlash redirect for sub pages', async () => {
-		const config = await getConfig();
-
-		const subpathRoute = config.routes.find((r) => r.src === '/subpage');
-		assert.notEqual(subpathRoute, undefined);
-		assert.equal(subpathRoute.headers.Location, '/subpage/');
-	});
-
-	it('does not define trailingSlash redirect for root page', async () => {
-		const config = await getConfig();
-		assert.equal(
-			config.routes.find((r) => r.src === '/'),
-			undefined
-		);
+	it('throws an error for invalid redirects', async () => {
+		const fails = await loadFixture({
+			root: './fixtures/redirects/',
+			redirects: {
+				// Invalid source syntax
+				'/blog/(![...slug]': '/team/articles/[...slug]',
+			},
+		});
+		await assert.rejects(() => fails.build(), {
+			name: 'AstroUserError',
+			message:
+				'Error generating redirects: Redirect at index 0 has invalid `source` regular expression "/blog/(!:slug*".',
+		});
 	});
 });

packages/vercel/test/static.test.js

@@ -17,7 +17,7 @@ describe('static routing', () => {
 		const deploymentConfig = JSON.parse(await fixture.readFile('../.vercel/output/config.json'));
 		// change the index if necesseary
 		assert.deepEqual(deploymentConfig.routes[2], {
-			src: '/.*',
+			src: '^/.*$',
 			dest: '/404.html',
 			status: 404,
 		});