fix(underscore-redirects): respect trailingSlash config in redirects

.changeset/thin-memes-boil.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/underscore-redirects': patch
+---
+
+Fixes generated redirect files to respect Astro’s `trailingSlash` configuration, so redirect routes work with the expected URL format in built output instead of returning a 404 when accessed with a trailing slash.

packages/integrations/netlify/test/functions/redirects.test.js

@@ -16,9 +16,8 @@ describe(
 		it('Creates a redirects file', async () => {
 			const redirects = await fixture.readFile('./_redirects');
 			const parts = redirects.split(/\s+/);
-			assert.deepEqual(parts, ['', '/other', '/', '301', '']);
-			// Snapshots are not supported in Node.js test yet (https://github.com/nodejs/node/issues/48260)
-			assert.equal(redirects, '\n/other    /       301\n');
+			// based on https://github.com/withastro/astro/issues/16030 for the default option `trailingSlash: 'ignore'` both variants should be generated
+			assert.deepEqual(parts, ['', '/other/', '/', '301', '/other', '/', '301', '']);
 		});
 
 		it('Does not create .html files', async () => {

packages/integrations/netlify/test/static/redirects.test.js

@@ -13,13 +13,22 @@ describe('SSG - Redirects', () => {
 	it('Creates a redirects file', async () => {
 		const redirects = await fixture.readFile('./_redirects');
 		const parts = redirects.split(/\s+/);
+		// based on https://github.com/withastro/astro/issues/16030 for the default option `trailingSlash: 'ignore'` both variants should be generated
 		assert.deepEqual(parts, [
 			'',
 
+			'/two/',
+			'/',
+			'302',
+
 			'/two',
 			'/',
 			'302',
 
+			'/other/',
+			'/',
+			'301',
+
 			'/other',
 			'/',
 			'301',

packages/underscore-redirects/src/astro.ts

@@ -17,7 +17,7 @@ function getRedirectStatus(route: IntegrationResolvedRoute): ValidRedirectStatus
 }
 
 interface CreateRedirectsFromAstroRoutesParams {
-	config: Pick<AstroConfig, 'build' | 'output' | 'base'>;
+	config: Pick<AstroConfig, 'build' | 'output' | 'base' | 'trailingSlash'>;
 	/**
 	 * Maps a `RouteData` to a dynamic target
 	 */
@@ -27,6 +27,35 @@ interface CreateRedirectsFromAstroRoutesParams {
 	assets: HookParameters<'astro:build:done'>['assets'];
 }
 
+/**
+ * Returns the path(s) to use for a redirect entry based on the trailingSlash config.
+ * - 'always': ensures the path ends with '/'
+ * - 'never': ensures the path does not end with '/'
+ * - 'ignore'(default): returns both with and without trailing slash variants
+ */
+export function getTrailingSlashPaths(
+	inputPath: string,
+	trailingSlash: 'always' | 'never' | 'ignore',
+): string[] {
+	if (inputPath === '/') {
+		return ['/'];
+	}
+
+	const hasTrailingSlash = inputPath.endsWith('/');
+	const withoutSlash = hasTrailingSlash ? inputPath.slice(0, -1) : inputPath;
+	const withSlash = hasTrailingSlash ? inputPath : inputPath + '/';
+
+	switch (trailingSlash) {
+		case 'always':
+			return [withSlash];
+		case 'never':
+			return [withoutSlash];
+		case 'ignore':
+		default:
+			return [withoutSlash, withSlash];
+	}
+}
+
 /**
  * Takes a set of routes and creates a Redirects object from them.
  */
@@ -57,13 +86,20 @@ export function createRedirectsFromAstroRoutes({
 				// Use `entrypoint` when available to keep trailing slashes in _redirects.
 				const inputPath =
 					route.type === 'redirect' && route.entrypoint ? route.entrypoint : route.pathname;
-				redirects.add({
-					dynamic: false,
-					input: `${base}${inputPath}`,
-					target: typeof route.redirect === 'object' ? route.redirect.destination : route.redirect,
-					status: getRedirectStatus(route),
-					weight: 2,
-				});
+
+				// Generate redirect entries based on trailingSlash config.
+				const trailingSlash = config.trailingSlash ?? 'ignore';
+				const paths = getTrailingSlashPaths(inputPath, trailingSlash);
+				for (const path of paths) {
+					redirects.add({
+						dynamic: false,
+						input: `${base}${path}`,
+						target:
+							typeof route.redirect === 'object' ? route.redirect.destination : route.redirect,
+						status: getRedirectStatus(route),
+						weight: 2,
+					});
+				}
 				continue;
 			}
 

packages/underscore-redirects/src/index.ts

@@ -1,6 +1,7 @@
 export {
 	createHostedRouteDefinition,
 	createRedirectsFromAstroRoutes,
+	getTrailingSlashPaths
 } from './astro.js';
 export { HostRoutes } from './host-route.js';
 export { printAsRedirects } from './print.js';

packages/underscore-redirects/test/astro.test.js

@@ -1,6 +1,6 @@
 import * as assert from 'node:assert/strict';
 import { describe, it } from 'node:test';
-import { createRedirectsFromAstroRoutes } from '../dist/index.js';
+import { createRedirectsFromAstroRoutes, getTrailingSlashPaths } from '../dist/index.js';
 
 describe('Astro', () => {
 	it('Creates a Redirects object from routes', () => {
@@ -25,4 +25,25 @@ describe('Astro', () => {
 
 		assert.equal(_redirects.definitions.length, 2);
 	});
+
+	it('Generates correct paths for root', () => {
+		assert.deepEqual(getTrailingSlashPaths('/', 'ignore'), ['/']);
+		assert.deepEqual(getTrailingSlashPaths('/', 'always'), ['/']);
+		assert.deepEqual(getTrailingSlashPaths('/', 'never'), ['/']);
+	});
+
+	it('Generates correct paths for trailingslash ignore', () => {
+		assert.deepEqual(getTrailingSlashPaths('/path', 'ignore'), ['/path', '/path/']);
+		assert.deepEqual(getTrailingSlashPaths('/path/', 'ignore'), ['/path', '/path/']);
+	});
+
+	it('Generates correct paths for trailingslash always', () => {
+		assert.deepEqual(getTrailingSlashPaths('/path', 'always'), ['/path/']);
+		assert.deepEqual(getTrailingSlashPaths('/path/', 'always'), ['/path/']);
+	});
+
+	it('Generates correct paths for trailingslash never', () => {
+		assert.deepEqual(getTrailingSlashPaths('/path', 'never'), ['/path']);
+		assert.deepEqual(getTrailingSlashPaths('/path/', 'never'), ['/path']);
+	});
 });