feat: add support for styled RSS feeds (#2371)

.changeset/five-crabs-sparkle.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Add support for styled RSS feeds using the new `stylesheet` option

docs/src/pages/en/guides/rss.md

@@ -4,7 +4,7 @@ title: RSS
 description: An intro to RSS in Astro
 ---
 
-Astro supports fast, automatic RSS feed generation for blogs and other content websites.
+Astro supports fast, automatic RSS feed generation for blogs and other content websites. For more information about RSS feeds in general, see [aboutfeeds.com](https://aboutfeeds.com/).
 
 You can create an RSS feed from any Astro page that uses a `getStaticPaths()` function for routing. Only dynamic routes can use `getStaticPaths()` today (see [Routing](/en/core-concepts/routing)).
 
@@ -22,6 +22,8 @@ export async function getStaticPaths({rss}) {
   rss({
     // The RSS Feed title, description, and custom metadata.
     title: 'Don\'s Blog',
+    // See "Styling" section below
+    stylesheet: true,
     description: 'An example blog on Astro',
     customData: `<language>en-us</language>`,
     // The list of items for your RSS feed, sorted.
@@ -41,3 +43,11 @@ export async function getStaticPaths({rss}) {
 ```
 
 Note: RSS feeds will **not** be built during development. Currently, RSS feeds are only generated during your final build.
+
+### Styling
+
+RSS Feeds can be styled with an XSL stylesheet for a more pleasant user experience when they are opened directly in a browser. By default, Astro does not set a stylesheet for RSS feeds, but it can be enabled by setting the `stylesheet` option.
+
+Astro can automatically use [Pretty Feed](https://github.com/genmon/aboutfeeds/blob/main/tools/pretty-feed-v3.xsl), a popular open-source XSL stylesheet. To enable this behavior, pass `stylesheet: true`. 
+
+If you'd like to use a custom XSL stylesheet, you can pass a string value like `stylesheet: '/my-custom-stylesheet.xsl'`. This file should be in your `public/` directory (in this case, `public/my-custom-stylesheet.xsl`).

packages/astro/src/@types/astro.ts

@@ -339,6 +339,12 @@ export interface RSS {
 	description: string;
 	/** Specify arbitrary metadata on opening <xml> tag */
 	xmlns?: Record<string, string>;
+	/** 
+	 * If false (default), does not include XSL stylesheet. 
+	 * If true, automatically includes 'pretty-feed-v3'.
+	 * If a string value, specifies a local custom XSL stylesheet, for example '/custom-feed.xsl'.
+	 */
+	stylesheet?: string | boolean;
 	/** Specify custom data in opening of file */
 	customData?: string;
 	/**
@@ -364,7 +370,8 @@ export interface RSS {
 
 export type RSSFunction = (args: RSS) => void;
 
-export type RSSResult = { url: string; xml?: string };
+export type FeedResult = { url: string; content?: string; };
+export type RSSResult = { xml: FeedResult; xsl?: FeedResult };
 
 export type SSRError = Error & vite.ErrorPayload['err'];
 

packages/astro/src/core/build/page-data.ts

@@ -79,11 +79,22 @@ export async function collectPagesData(opts: CollectPagesDataOptions): Promise<C
 					throw err;
 				});
 			if (result.rss?.xml) {
-				const rssFile = new URL(result.rss.url.replace(/^\/?/, './'), astroConfig.dist);
+				const { url, content } = result.rss.xml;
-				if (assets[fileURLToPath(rssFile)]) {
+				if (content) {
-					throw new Error(`[getStaticPaths] RSS feed ${result.rss.url} already exists.\nUse \`rss(data, {url: '...'})\` to choose a unique, custom URL. (${route.component})`);
+					const rssFile = new URL(url.replace(/^\/?/, './'), astroConfig.dist);
+					if (assets[fileURLToPath(rssFile)]) {
+						throw new Error(`[getStaticPaths] RSS feed ${url} already exists.\nUse \`rss(data, {url: '...'})\` to choose a unique, custom URL. (${route.component})`);
+					}
+					assets[fileURLToPath(rssFile)] = content;
 				}
-				assets[fileURLToPath(rssFile)] = result.rss.xml;
+			}
+			if (result.rss?.xsl?.content) {
+				const { url, content } = result.rss.xsl;
+				const stylesheetFile = new URL(url.replace(/^\/?/, './'), astroConfig.dist);
+				if (assets[fileURLToPath(stylesheetFile)]) {
+					throw new Error(`[getStaticPaths] RSS feed stylesheet ${url} already exists.\nUse \`rss(data, {stylesheet: '...'})\` to choose a unique, custom URL. (${route.component})`);
+				}
+				assets[fileURLToPath(stylesheetFile)] = content;
 			}
 			allPages[route.component] = {
 				route,

packages/astro/src/core/ssr/rss.ts

@@ -1,7 +1,7 @@
-import type { RSSFunction, RSS, RSSResult, RouteData } from '../../@types/astro';
+import type { RSSFunction, RSS, RSSResult, FeedResult, RouteData } from '../../@types/astro';
 
 import { XMLValidator } from 'fast-xml-parser';
-import { canonicalURL } from '../util.js';
+import { canonicalURL, PRETTY_FEED_V3 } from '../util.js';
 
 /** Validates getStaticPaths.rss */
 export function validateRSS(args: GenerateRSSArgs): void {
@@ -20,7 +20,11 @@ export function generateRSS(args: GenerateRSSArgs): string {
 	const { srcFile, feedURL, rssData, site } = args;
 	if ((rssData as any).item) throw new Error(`[${srcFile}] rss() \`item()\` function was deprecated, and is now \`items: object[]\`.`);
 
-	let xml = `<?xml version="1.0" encoding="UTF-8"?><rss version="2.0"`;
+	let xml = `<?xml version="1.0" encoding="UTF-8"?>`;
+	if (typeof rssData.stylesheet === 'string') {
+		xml += `<?xml-stylesheet href="${rssData.stylesheet}" type="text/xsl"?>`;
+	}
+	xml += `<rss version="2.0"`;
 
 	// xmlns
 	if (rssData.xmlns) {
@@ -72,18 +76,35 @@ export function generateRSS(args: GenerateRSSArgs): string {
 	return xml;
 }
 
+export function generateRSSStylesheet() {
+	return PRETTY_FEED_V3;
+}
+
 /** Generated function to be run  */
 export function generateRssFunction(site: string | undefined, route: RouteData): { generator: RSSFunction; rss?: RSSResult } {
 	let result: RSSResult = {} as any;
 	return {
-		generator: function rssUtility(args: any) {
+		generator: function rssUtility(args: RSS) {
 			if (!site) {
 				throw new Error(`[${route.component}] rss() tried to generate RSS but "buildOptions.site" missing in astro.config.mjs`);
 			}
 			const { dest, ...rssData } = args;
 			const feedURL = dest || '/rss.xml';
-			result.url = feedURL;
+			if (rssData.stylesheet === true) {
-			result.xml = generateRSS({ rssData, site, srcFile: route.component, feedURL });
+				rssData.stylesheet = feedURL.replace(/\.xml$/, '.xsl');
+				result.xsl = {
+					url: rssData.stylesheet,
+					content: generateRSSStylesheet(),
+				}
+			} else if (typeof rssData.stylesheet === 'string') {
+				result.xsl = {
+					url: rssData.stylesheet,
+				}
+			}
+			result.xml = {
+				url: feedURL,
+				content: generateRSS({ rssData, site, srcFile: route.component, feedURL })
+			};
 		},
 		rss: result,
 	};