feat: support Rolldown

.changeset/nine-ads-tease.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': minor
+---
+
+feat: add support for Rolldown. See https://vite.dev/guide/rolldown.html#how-to-try-rolldown for details about how to try it. You will also need `vite-plugin-svelte@^6.0.0-next.0` and `vite@^7.0.0-beta.0`.

package.json

@@ -38,6 +38,7 @@
 	"pnpm": {
 		"onlyBuiltDependencies": [
 			"esbuild",
+			"rolldown",
 			"sharp",
 			"svelte-preprocess",
 			"workerd"

packages/adapter-auto/package.json

@@ -41,7 +41,7 @@
 	},
 	"devDependencies": {
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"@types/node": "^18.19.48",
 		"typescript": "^5.3.3",
 		"vitest": "catalog:"

packages/adapter-cloudflare/test/apps/pages/package.json

@@ -11,10 +11,10 @@
 	},
 	"devDependencies": {
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"server-side-dep": "file:server-side-dep",
 		"svelte": "^5.23.1",
-		"vite": "^6.2.7",
+		"vite": "catalog:",
 		"wrangler": "^4.14.3"
 	},
 	"type": "module"

packages/adapter-cloudflare/test/apps/workers/package.json

@@ -11,10 +11,10 @@
 	},
 	"devDependencies": {
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"server-side-dep": "file:server-side-dep",
 		"svelte": "^5.23.1",
-		"vite": "^6.2.7",
+		"vite": "catalog:",
 		"wrangler": "^4.14.3"
 	},
 	"type": "module"

packages/adapter-netlify/package.json

@@ -51,7 +51,7 @@
 		"@rollup/plugin-json": "^6.1.0",
 		"@rollup/plugin-node-resolve": "^16.0.0",
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"@types/node": "^18.19.48",
 		"@types/set-cookie-parser": "^2.4.7",
 		"rollup": "^4.14.2",

packages/adapter-node/package.json

@@ -44,7 +44,7 @@
 	"devDependencies": {
 		"@polka/url": "^1.0.0-next.28",
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"@types/node": "^18.19.48",
 		"polka": "^1.0.0-next.28",
 		"sirv": "^3.0.0",

packages/adapter-static/package.json

@@ -41,12 +41,12 @@
 	"devDependencies": {
 		"@playwright/test": "catalog:",
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"@types/node": "^18.19.48",
 		"sirv": "^3.0.0",
 		"svelte": "^5.23.1",
 		"typescript": "^5.3.3",
-		"vite": "^6.2.7"
+		"vite": "catalog:"
 	},
 	"peerDependencies": {
 		"@sveltejs/kit": "^2.0.0"

packages/adapter-static/test/apps/prerendered/package.json

@@ -10,10 +10,10 @@
 	},
 	"devDependencies": {
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"sirv-cli": "^3.0.0",
 		"svelte": "^5.23.1",
-		"vite": "^6.2.7"
+		"vite": "catalog:"
 	},
 	"type": "module"
 }

packages/adapter-static/test/apps/spa/package.json

@@ -11,10 +11,10 @@
 	"devDependencies": {
 		"@sveltejs/adapter-node": "workspace:^",
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"sirv-cli": "^3.0.0",
 		"svelte": "^5.23.1",
-		"vite": "^6.2.7"
+		"vite": "catalog:"
 	},
 	"type": "module"
 }

packages/adapter-vercel/package.json

@@ -45,7 +45,7 @@
 	},
 	"devDependencies": {
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"@types/node": "^18.19.48",
 		"typescript": "^5.3.3",
 		"vitest": "catalog:"

packages/enhanced-img/package.json

@@ -43,13 +43,13 @@
 		"zimmerframe": "^1.1.2"
 	},
 	"devDependencies": {
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"@types/estree": "^1.0.5",
 		"@types/node": "^18.19.48",
 		"rollup": "^4.27.4",
 		"svelte": "^5.23.1",
 		"typescript": "^5.6.3",
-		"vite": "^6.2.7",
+		"vite": "catalog:",
 		"vitest": "catalog:"
 	},
 	"peerDependencies": {

packages/enhanced-img/test/markup-plugin.spec.js

@@ -18,7 +18,7 @@ it('Image preprocess snapshot test', async () => {
 			throw new Error(`unrecognized id ${id}`);
 		}
 	});
-	const plugin_context = /** @type {import('rollup').TransformPluginContext} */ (
+	const plugin_context = /** @type {import('vite').Rollup.TransformPluginContext} */ (
 		/** @type {unknown} */ ({
 			// @ts-ignore
 			resolve(url) {
@@ -27,7 +27,7 @@ it('Image preprocess snapshot test', async () => {
 		})
 	);
 	const transform =
-		/** @type {(this: import('rollup').TransformPluginContext, code: string, id: string, options?: {ssr?: boolean;}) => Promise<import('rollup').TransformResult>} */ (
+		/** @type {(this: import('vite').Rollup.TransformPluginContext, code: string, id: string, options?: {ssr?: boolean;}) => Promise<import('rollup').TransformResult>} */ (
 			vite_plugin.transform
 		);
 	const transformed = await transform.call(

packages/kit/package.json

@@ -34,7 +34,7 @@
 	},
 	"devDependencies": {
 		"@playwright/test": "catalog:",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"@types/connect": "^3.4.38",
 		"@types/node": "^18.19.48",
 		"@types/set-cookie-parser": "^2.4.7",
@@ -43,13 +43,13 @@
 		"svelte": "^5.23.1",
 		"svelte-preprocess": "^6.0.0",
 		"typescript": "^5.3.3",
-		"vite": "^6.2.7",
+		"vite": "catalog:",
 		"vitest": "catalog:"
 	},
 	"peerDependencies": {
-		"@sveltejs/vite-plugin-svelte": "^3.0.0 || ^4.0.0-next.1 || ^5.0.0",
+		"@sveltejs/vite-plugin-svelte": "^3.0.0 || ^4.0.0-next.1 || ^5.0.0 || ^6.0.0-next.0",
 		"svelte": "^4.0.0 || ^5.0.0-next.0",
-		"vite": "^5.0.3 || ^6.0.0"
+		"vite": "^5.0.3 || ^6.0.0 || ^7.0.0-beta.0"
 	},
 	"bin": {
 		"svelte-kit": "svelte-kit.js"

packages/kit/src/exports/vite/build/build_server.js

@@ -14,22 +14,20 @@ import { create_node_analyser } from '../static_analysis/index.js';
  * @param {import('vite').Manifest} server_manifest
  * @param {import('vite').Manifest | null} client_manifest
  * @param {import('vite').Rollup.OutputBundle | null} server_bundle
- * @param {import('vite').Rollup.RollupOutput['output'] | null} client_bundle
+ * @param {import('vite').Rollup.RollupOutput['output'] | null} client_chunks
  * @param {import('types').RecursiveRequired<import('types').ValidatedConfig['kit']['output']>} output_config
  * @param {Map<string, { page_options: Record<string, any> | null, children: string[] }>} static_exports
  */
-export async function build_server_nodes(out, kit, manifest_data, server_manifest, client_manifest, server_bundle, client_bundle, output_config, static_exports) {
+export async function build_server_nodes(out, kit, manifest_data, server_manifest, client_manifest, server_bundle, client_chunks, output_config, static_exports) {
 	mkdirp(`${out}/server/nodes`);
 	mkdirp(`${out}/server/stylesheets`);
 
 	/** @type {Map<string, string>} */
 	const stylesheets_to_inline = new Map();
 
-	if (server_bundle && client_bundle && kit.inlineStyleThreshold > 0) {
-		const client = get_stylesheets(client_bundle);
-
-		const server_chunks = Object.values(server_bundle);
-		const server = get_stylesheets(server_chunks);
+	if (server_bundle && client_chunks && kit.inlineStyleThreshold > 0) {
+		const client = get_stylesheets(client_chunks);
+		const server = get_stylesheets(Object.values(server_bundle));
 
 		// map server stylesheet name to the client stylesheet name
 		for (const [id, client_stylesheet] of client.stylesheets_used) {

packages/kit/src/exports/vite/build/build_service_worker.js

@@ -103,7 +103,8 @@ export async function build_service_worker(
 				},
 				output: {
 					// .mjs so that esbuild doesn't incorrectly inject `export` https://github.com/vitejs/vite/issues/15379
-					entryFileNames: 'service-worker.mjs',
+					// @ts-expect-error `vite.rolldownVersion` only exists in `rolldown-vite`
+					entryFileNames: `service-worker.${vite.rolldownVersion ? 'js' : 'mjs'}`,
 					assetFileNames: `${kit.appDir}/immutable/assets/[name].[hash][extname]`,
 					inlineDynamicImports: true
 				}
@@ -129,5 +130,8 @@ export async function build_service_worker(
 	});
 
 	// rename .mjs to .js to avoid incorrect MIME types with ancient webservers
-	fs.renameSync(`${out}/client/service-worker.mjs`, `${out}/client/service-worker.js`);
+	// @ts-expect-error `vite.rolldownVersion` only exists in `rolldown-vite`
+	if (!vite.rolldownVersion) {
+		fs.renameSync(`${out}/client/service-worker.mjs`, `${out}/client/service-worker.js`);
+	}
 }

packages/kit/src/exports/vite/index.js

@@ -182,6 +182,7 @@ let manifest_data;
  * @return {Promise<import('vite').Plugin[]>}
  */
 async function kit({ svelte_config }) {
+	/** @type {import('vite')} */
 	const vite = await import_peer('vite');
 
 	const { kit } = svelte_config;
@@ -694,13 +695,15 @@ Tips:
 								assetFileNames: `${prefix}/assets/[name].[hash][extname]`,
 								hoistTransitiveImports: false,
 								sourcemapIgnoreList,
-								manualChunks: split ? undefined : () => 'bundle',
 								inlineDynamicImports: false
 							},
 							preserveEntrySignatures: 'strict',
 							onwarn(warning, handler) {
 								if (
-									warning.code === 'MISSING_EXPORT' &&
+									// @ts-expect-error `vite.rolldownVersion` only exists in `rolldown-vite`
+									(vite.rolldownVersion
+										? warning.code === 'IMPORT_IS_UNDEFINED'
+										: warning.code === 'MISSING_EXPORT') &&
 									warning.id === `${kit.outDir}/generated/client-optimized/app.js`
 								) {
 									// ignore e.g. undefined `handleError` hook when
@@ -725,7 +728,25 @@ Tips:
 							}
 						}
 					}
+					// TODO: enabling `experimental.enableNativePlugin` causes styles to not be applied
+					// see https://github.com/vitejs/rolldown-vite/issues/213
+					// experimental: {
+					// 	enableNativePlugin: true
+					// }
 				};
+
+				if (!split && new_config.build?.rollupOptions?.output) {
+					const output_options = /** @type {import('vite').Rollup.OutputOptions} */ (
+						new_config.build.rollupOptions.output
+					);
+					// @ts-expect-error `vite.rolldownVersion` only exists in `rolldown-vite`
+					if (vite.rolldownVersion) {
+						output_options.inlineDynamicImports = true;
+					} else {
+						/** @type {import('rollup').OutputOptions} */ (output_options).manualChunks = () =>
+							'bundle';
+					}
+				}
 			} else {
 				new_config = {
 					appType: 'custom',
@@ -738,6 +759,11 @@ Tips:
 						}
 					},
 					publicDir: kit.files.assets
+					// TODO: enabling `experimental.enableNativePlugin` causes styles to not be applied
+					// see https://github.com/vitejs/rolldown-vite/issues/213
+					// experimental: {
+					// 	enableNativePlugin: true
+					// }
 				};
 			}
 
@@ -779,7 +805,8 @@ Tips:
 		renderChunk(code, chunk) {
 			if (code.includes('__SVELTEKIT_TRACK__')) {
 				return {
-					code: code.replace(/__SVELTEKIT_TRACK__\('(.+?)'\)/g, (_, label) => {
+					// Rolldown changes our single quotes to double quotes so we need it in the regex too
+					code: code.replace(/__SVELTEKIT_TRACK__\(['"](.+?)['"]\)/g, (_, label) => {
 						(tracked_features[chunk.name + '.js'] ??= []).push(label);
 						// put extra whitespace at the end of the comment to preserve the source size and avoid interfering with source maps
 						return `/* track ${label}            */`;
@@ -960,7 +987,7 @@ Tips:
 					};
 
 					if (svelte_config.kit.output.bundleStrategy === 'inline') {
-						const style = /** @type {import('rollup').OutputAsset} */ (
+						const style = /** @type {import('vite').Rollup.OutputAsset} */ (
 							client_chunks.find(
 								(chunk) =>
 									chunk.type === 'asset' &&
@@ -1035,7 +1062,7 @@ Tips:
 							...vite_config,
 							build: {
 								...vite_config.build,
-								minify: initial_config.build?.minify ?? 'esbuild'
+								minify: initial_config.build?.minify ?? true
 							}
 						},
 						manifest_data,

packages/kit/src/runtime/client/client.js

@@ -712,9 +712,12 @@ async function load_node({ loader, parent, url, params, route, server_data_node
 								: await resource.blob(),
 						cache: resource.cache,
 						credentials: resource.credentials,
-						// the headers are undefined on the server if the Headers object is empty
-						// so we need to make sure they are also undefined here if there are no headers
-						headers: [...resource.headers].length ? resource.headers : undefined,
+						// the server sets headers to `undefined` if there are no headers but
+						// the client defaults to an empty Headers object in the Request object.
+						// To keep the two values in sync, we explicitly set the headers to `undefined`.
+						// Also, not sure why, but sometimes 0 is evaluated as truthy so we need to
+						// explicitly compare the headers length to a number here
+						headers: [...resource.headers].length > 0 ? resource?.headers : undefined,
 						integrity: resource.integrity,
 						keepalive: resource.keepalive,
 						method: resource.method,

packages/kit/test/apps/amp/package.json

@@ -15,13 +15,13 @@
 	"devDependencies": {
 		"@sveltejs/amp": "workspace:^",
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"cross-env": "^7.0.3",
 		"dropcss": "^1.0.16",
 		"svelte": "^5.23.1",
 		"svelte-check": "^4.1.1",
 		"typescript": "^5.5.4",
-		"vite": "^6.2.7"
+		"vite": "catalog:"
 	},
 	"type": "module"
 }

packages/kit/test/apps/basics/package.json

@@ -18,13 +18,13 @@
 	},
 	"devDependencies": {
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"cross-env": "^7.0.3",
 		"svelte": "^5.23.1",
 		"svelte-check": "^4.1.1",
 		"redirect-pkg": "file:./_test_dependencies/redirect-pkg",
 		"typescript": "^5.5.4",
-		"vite": "^6.2.7"
+		"vite": "catalog:"
 	},
 	"type": "module"
 }

packages/kit/test/apps/basics/test/client.test.js

@@ -1268,7 +1268,7 @@
 			expect(page.locator('p.loadingfail')).toBeHidden();
 		});
 
 		test('Catches fetch errors from server load functions (direct hit)', async ({ page }) => {
 			page.goto('/streaming/server-error');
 			await expect(page.locator('p.eager')).toHaveText('eager');
 			await expect(page.locator('p.fail')).toHaveText('fail');
@@ -1494,10 +1494,10 @@
 		await page.goto('/reroute/external');
 		const current_url = new URL(page.url());
 
-		//click the link with the text External URL
+		// click the link with the text External URL
 		await page.click("a[data-test='external-url']");
 
-		//The URl should not have the same origin as the current URL
+		// The URL should not have the same origin as the current URL
 		const new_url = new URL(page.url());
 		expect(current_url.origin).not.toEqual(new_url.origin);
 	});

packages/kit/test/apps/dev-only/package.json

@@ -12,7 +12,7 @@
 	},
 	"devDependencies": {
 		"@sveltejs/kit": "workspace:^",
-		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"@sveltejs/vite-plugin-svelte": "catalog:",
 		"cross-env": "^7.0.3",
 		"e2e-test-dep-error": "file:./_test_dependencies/cjs-only",
 		"e2e-test-dep-hooks": "file:./_test_dependencies/cjs-only",
@@ -27,7 +27,7 @@
 		"svelte": "^5.23.1",
 		"svelte-check": "^4.1.1",
 		"typescript": "^5.5.4",
-		"vite": "^6.2.7"
+		"vite": "catalog:"
 	},
 	"type": "module"
 }