fix: ISR support for adapter-vercel

.changeset/pretty-kids-camp.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-vercel': patch
+---
+
+fix: get ISR working on Vercel

documentation/docs/25-build-and-deploy/90-adapter-vercel.md

@@ -88,18 +88,14 @@ export const config = {
 		// Setting the value to `false` means it will never expire.
 		expiration: 60,
 
-		// Option group number of the asset. Assets with the same group number will all be re-validated at the same time.
-		group: 1,
-
 		// Random token that can be provided in the URL to bypass the cached version of the asset, by requesting the asset
 		// with a __prerender_bypass=<token> cookie.
 		//
 		// Making a `GET` or `HEAD` request with `x-prerender-revalidate: <token>` will force the asset to be re-validated.
 		bypassToken: BYPASS_TOKEN,
 
-		// List of query string parameter names that will be cached independently.
-		// If an empty array, query values are not considered for caching.
-		// If `undefined` each unique query value is cached independently
+		// List of valid query parameters. Other parameters (such as utm tracking codes) will be ignored,
+		// ensuring that they do not result in content being regenerated unnecessarily
 		allowQuery: ['search']
 	}
 };

packages/adapter-vercel/files/serverless.js

@@ -11,11 +11,25 @@ await server.init({
 	env: /** @type {Record<string, string>} */ (process.env)
 });
 
+const DATA_SUFFIX = '/__data.json';
+
 /**
  * @param {import('http').IncomingMessage} req
  * @param {import('http').ServerResponse} res
  */
 export default async (req, res) => {
+	if (req.url) {
+		const [path, search] = req.url.split('?');
+
+		const params = new URLSearchParams(search);
+		const pathname = params.get('__pathname');
+
+		if (pathname) {
+			params.delete('__pathname');
+			req.url = `${pathname}${path.endsWith(DATA_SUFFIX) ? DATA_SUFFIX : ''}?${params}`;
+		}
+	}
+
 	/** @type {Request} */
 	let request;
 

packages/adapter-vercel/index.d.ts

@@ -36,10 +36,6 @@ export interface ServerlessConfig {
 		 * Expiration time (in seconds) before the cached asset will be re-generated by invoking the Serverless Function. Setting the value to `false` means it will never expire.
 		 */
 		expiration: number | false;
-		/**
-		 * Option group number of the asset. Assets with the same group number will all be re-validated at the same time.
-		 */
-		group?: number;
 		/**
 		 * Random token that can be provided in the URL to bypass the cached version of the asset, by requesting the asset
 		 * with a __prerender_bypass=<token> cookie.

packages/adapter-vercel/index.js

@@ -76,22 +76,6 @@ const plugin = function (defaults = {}) {
 					`${dirs.functions}/${name}.func`,
 					config
 				);
-
-				if (config.isr) {
-					write(
-						`${dirs.functions}/${name}.prerender-config.json`,
-						JSON.stringify(
-							{
-								expiration: config.isr.expiration,
-								group: config.isr.group,
-								bypassToken: config.isr.bypassToken,
-								allowQuery: config.isr.allowQuery
-							},
-							null,
-							'\t'
-						)
-					);
-				}
 			}
 
 			/**
@@ -158,6 +142,9 @@ const plugin = function (defaults = {}) {
 			/** @type {Map<string, string>} */
 			const functions = new Map();
 
+			/** @type {Map<import('@sveltejs/kit').RouteDefinition<import('.').Config>, { expiration: number | false, bypassToken: string | undefined, allowQuery: string[], group: number, passQuery: true }>} */
+			const isr_config = new Map();
+
 			// group routes by config
 			for (const route of builder.routes) {
 				if (route.prerender === true) continue;
@@ -175,6 +162,20 @@ const plugin = function (defaults = {}) {
 
 				const config = { runtime, ...defaults, ...route.config };
 
+				if (config.isr) {
+					if (config.isr.allowQuery?.includes('__pathname')) {
+						throw new Error('__pathname is a reserved query parameter for isr.allowQuery');
+					}
+
+					isr_config.set(route, {
+						expiration: config.isr.expiration,
+						bypassToken: config.isr.bypassToken,
+						allowQuery: ['__pathname', ...(config.isr.allowQuery ?? [])],
+						group: isr_config.size + 1,
+						passQuery: true
+					});
+				}
+
 				const hash = hash_config(config);
 
 				// first, check there are no routes with incompatible configs that will be merged
@@ -238,12 +239,47 @@ const plugin = function (defaults = {}) {
 					src = '^/?';
 				}
 
-				src += '(?:/__data.json)?$';
-
 				const name = functions.get(pattern);
 				if (name) {
-					static_config.routes.push({ src, dest: `/${name}` });
-					functions.delete(pattern);
+					const isr = isr_config.get(route);
+					if (isr) {
+						const base = `${dirs.functions}/${route.id.slice(1)}`;
+						builder.mkdirp(base);
+
+						const target = `${dirs.functions}/${name}.func`;
+						const relative = path.relative(path.dirname(base), target);
+
+						// create a symlink to the actual function, but use the
+						// route name so that we can derive the correct URL
+						fs.symlinkSync(relative, `${base}.func`);
+						fs.symlinkSync(`../${relative}`, `${base}/__data.json.func`);
+
+						let i = 1;
+						const pathname = route.segments
+							.map((segment) => {
+								return segment.dynamic ? `$${i++}` : segment.content;
+							})
+							.join('/');
+
+						const json = JSON.stringify(isr, null, '\t');
+
+						write(`${base}.prerender-config.json`, json);
+						write(`${base}/__data.json.prerender-config.json`, json);
+
+						const q = `?__pathname=/${pathname}`;
+
+						static_config.routes.push({
+							src: src + '$',
+							dest: `${route.id}${q}`
+						});
+
+						static_config.routes.push({
+							src: src + '/__data.json$',
+							dest: `${route.id}/__data.json${q}`
+						});
+					} else {
+						static_config.routes.push({ src: src + '(?:/__data.json)?$', dest: `/${name}` });
+					}
 				}
 			}
 
@@ -266,11 +302,7 @@ function hash_config(config) {
 		config.external ?? '',
 		config.regions ?? '',
 		config.memory ?? '',
-		config.maxDuration ?? '',
-		config.isr?.expiration ?? '',
-		config.isr?.group ?? '',
-		config.isr?.bypassToken ?? '',
-		config.isr?.allowQuery ?? ''
+		config.maxDuration ?? ''
 	].join('/');
 }
 
@@ -400,22 +432,21 @@ async function create_function_bundle(builder, entry, dir, config) {
 		}
 	}
 
+	const files = Array.from(traced.fileList);
+
 	// find common ancestor directory
 	/** @type {string[]} */
-	let common_parts = [];
+	let common_parts = files[0]?.split(path.sep) ?? [];
 
-	for (const file of traced.fileList) {
-		if (common_parts) {
-			const parts = file.split(path.sep);
+	for (let i = 1; i < files.length; i += 1) {
+		const file = files[i];
+		const parts = file.split(path.sep);
 
-			for (let i = 0; i < common_parts.length; i += 1) {
-				if (parts[i] !== common_parts[i]) {
-					common_parts = common_parts.slice(0, i);
-					break;
-				}
+		for (let i = 0; i < common_parts.length; i += 1) {
+			if (parts[i] !== common_parts[i]) {
+				common_parts = common_parts.slice(0, i);
+				break;
 			}
-		} else {
-			common_parts = path.dirname(file).split(path.sep);
 		}
 	}