feat: support Rolldown

package.json

@@ -23,10 +23,10 @@
 	},
 	"devDependencies": {
 		"@changesets/cli": "^2.27.11",
+		"@playwright/test": "catalog:",
 		"@sveltejs/eslint-config": "^8.1.0",
 		"@svitejs/changesets-changelog-github-compact": "^1.1.0",
 		"eslint": "^9.6.0",
-		"@playwright/test": "catalog:",
 		"prettier": "^3.1.1",
 		"prettier-plugin-svelte": "^3.1.2",
 		"typescript-eslint": "^8.24.0"
@@ -36,8 +36,12 @@
 		"pnpm": ">=9.0.0"
 	},
 	"pnpm": {
+		"overrides": {
+			"vite": "npm:rolldown-vite@latest"
+		},
 		"onlyBuiltDependencies": [
 			"esbuild",
+			"rolldown",
 			"sharp",
 			"svelte-preprocess",
 			"workerd"

packages/enhanced-img/src/vite-plugin.js

@@ -193,7 +193,7 @@ export function image_plugin(imagetools_plugin) {
 
 /**
  * @param {string} resolved_id
- * @param {import('vite').Rollup.PluginContext} plugin_context
+ * @param {import('vite').Rolldown.PluginContext} plugin_context
  * @param {import('vite').Plugin} imagetools_plugin
  * @returns {Promise<import('vite-imagetools').Picture>}
  */

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').Rolldown.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').Rolldown.TransformPluginContext, code: string, id: string, options?: {ssr?: boolean;}) => Promise<import('rollup').TransformResult>} */ (
 			vite_plugin.transform
 		);
 	const transformed = await transform.call(

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

@@ -103,7 +103,7 @@ 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',
+					entryFileNames: `service-worker.${vite.rolldownVersion ? 'js' : 'mjs'}`,
 					assetFileNames: `${kit.appDir}/immutable/assets/[name].[hash][extname]`,
 					inlineDynamicImports: true
 				}
@@ -129,5 +129,7 @@ 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`);
+	if (!vite.rolldownVersion) {
+		fs.renameSync(`${out}/client/service-worker.mjs`, `${out}/client/service-worker.js`);
+	}
 }

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

@@ -8,7 +8,6 @@ import * as module_ids from '../module_ids.js';
  * @param {string} [expected_error]
  */
 function check(graph, expected_error) {
-	// @ts-expect-error
 	const context = /** @type {import('vite').Rollup.PluginContext} */ ({
 		/** @param {string} id */
 		getModuleInfo(id) {

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

@@ -181,6 +181,7 @@ let manifest_data;
  * @return {Promise<import('vite').Plugin[]>}
  */
 async function kit({ svelte_config }) {
+	/** @type {import('vite')} */
 	const vite = await resolve_peer_dependency('vite');
 
 	const { kit } = svelte_config;
@@ -675,13 +676,12 @@ Tips:
 								assetFileNames: `${prefix}/assets/[name].[hash][extname]`,
 								hoistTransitiveImports: false,
 								sourcemapIgnoreList,
-								manualChunks: split ? undefined : () => 'bundle',
 								inlineDynamicImports: false
 							},
-							preserveEntrySignatures: 'strict',
 							onwarn(warning, handler) {
 								if (
-									warning.code === 'MISSING_EXPORT' &&
+									warning.code === 'IMPORT_IS_UNDEFINED' &&
+									// TODO: rolldown doesn't seem to provide `warning.id` so this condition is never true https://github.com/rolldown/rolldown/issues/4427
 									warning.id === `${kit.outDir}/generated/client-optimized/app.js`
 								) {
 									// ignore e.g. undefined `handleError` hook when
@@ -706,7 +706,32 @@ Tips:
 							}
 						}
 					}
+					// TODO: enabling `experimental.enableNativePlugin` causes styles to not be applied
+					// see https://vite.dev/guide/rolldown#enabling-native-plugins
+					// experimental: {
+					// 	enableNativePlugin: true
+					// }
 				};
+
+				if (!vite.rolldownVersion) {
+					// TODO: always set this once `preserveEntrySignatures` is implemented in rolldown
+					// https://github.com/rolldown/rolldown/issues/3500
+					// rolldown always does 'strict' in the meantime, so it's fine to only set this in non-rolldown mode
+					// @ts-ignore
+					new_config.build.rollupOptions.preserveEntrySignatures = 'strict';
+				}
+
+				if (!split && new_config.build?.rollupOptions?.output) {
+					const output_options = /** @type {import('vite').Rolldown.OutputOptions} */ (
+						new_config.build.rollupOptions.output
+					);
+					if (vite.rolldownVersion) {
+						output_options.inlineDynamicImports = true;
+					} else {
+						/** @type {import('rollup').OutputOptions} */ (output_options).manualChunks = () =>
+							'bundle';
+					}
+				}
 			} else {
 				new_config = {
 					appType: 'custom',
@@ -760,7 +785,8 @@ 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}            */`;
@@ -852,7 +878,7 @@ Tips:
 
 				secondary_build_started = true;
 
-				const { output } = /** @type {import('vite').Rollup.RollupOutput} */ (
+				const { output } = /** @type {import('vite').Rolldown.RolldownOutput} */ (
 					await vite.build({
 						configFile: vite_config.configFile,
 						// CLI args
@@ -950,7 +976,7 @@ Tips:
 					};
 
 					if (svelte_config.kit.output.bundleStrategy === 'inline') {
-						const style = /** @type {import('rollup').OutputAsset} */ (
+						const style = /** @type {import('vite').Rolldown.OutputAsset} */ (
 							output.find(
 								(chunk) =>
 									chunk.type === 'asset' &&
@@ -967,7 +993,7 @@ Tips:
 				}
 
 				const css = output.filter(
-					/** @type {(value: any) => value is import('vite').Rollup.OutputAsset} */
+					/** @type {(value: any) => value is import('vite').Rolldown.OutputAsset} */
 					(value) => value.type === 'asset' && value.fileName.endsWith('.css')
 				);
 
@@ -1028,7 +1054,7 @@ Tips:
 							...vite_config,
 							build: {
 								...vite_config.build,
-								minify: initial_config.build?.minify ?? 'esbuild'
+								minify: initial_config.build?.minify ?? 'oxc'
 							}
 						},
 						manifest_data,

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

@@ -706,9 +706,12 @@ 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/basics/test/client.test.js

@@ -1494,10 +1494,10 @@ test.describe('reroute', () => {
 		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);
 	});