fix: Dumber fix for error assertions

documentation/docs/60-appendix/10-faq.md

@@ -183,6 +183,12 @@ export default config;
 
 See [Vite's `configureServer` docs](https://vitejs.dev/guide/api-plugin.html#configureserver) for more details including how to control ordering.
 
+## Why is SvelteKit being loaded twice?
+
+Sometimes, due to incorrect configuration, SvelteKit and other libraries can end up being loaded twice. The most common cause for this is package misconfiguration -- either when a package depends on a specific version of `@sveltejs/kit` rather than listing it as a `peerDependency` or when a package is using an incorrect combination of `main`/`module`/`exports` configuration that's causing your code to load both an ESM and CJS copy of SvelteKit.
+
+SvelteKit will try to figure out when this is happening and warn you by logging to the console during build. If you see one of these logs, try using `pnpm why` or `npm ls` to determine which package is loading SvelteKit, then file an issue with that package.
+
 ## How do I use Yarn?
 
 ### Does it work with Yarn 2?

packages/kit/package.json

@@ -29,8 +29,7 @@
 		"mrmime": "^2.0.0",
 		"sade": "^1.8.1",
 		"set-cookie-parser": "^2.6.0",
-		"sirv": "^3.0.0",
-		"vitefu": "^1.0.6"
+		"sirv": "^3.0.0"
 	},
 	"devDependencies": {
 		"@playwright/test": "catalog:",

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

@@ -1 +1,3 @@
+import '../multi-load-test.js';
+
 export { sequence } from './sequence.js';

packages/kit/src/exports/index.js

@@ -8,6 +8,7 @@ import {
 	strip_data_suffix,
 	strip_resolution_suffix
 } from '../runtime/pathname.js';
+import './multi-load-test.js';
 
 export { VERSION } from '../version.js';
 
@@ -85,8 +86,14 @@ export function error(status, body) {
  * @return {e is (HttpError & { status: T extends undefined ? never : T })}
  */
 export function isHttpError(e, status) {
-	if (!(e instanceof HttpError)) return false;
-	return !status || e.status === status;
+	return (
+		typeof e === 'object' &&
+		e !== null &&
+		Object.hasOwn(e, '_tag') &&
+		Object.hasOwn(e, 'status') &&
+		/** @type {{ _tag: string; }} */ (e)._tag === 'SvelteKitHttpError' &&
+		(!status || /** @type {{ status: number }} */ (e).status === status)
+	);
 }
 
 /**
@@ -124,7 +131,12 @@ export function redirect(status, location) {
  * @return {e is Redirect}
  */
 export function isRedirect(e) {
-	return e instanceof Redirect;
+	return (
+		typeof e === 'object' &&
+		e !== null &&
+		Object.hasOwn(e, '_tag') &&
+		/** @type {{ _tag: string }} */ (e)._tag === 'SvelteKitRedirect'
+	);
 }
 
 /**
@@ -213,7 +225,12 @@ export function fail(status, data) {
  * @return {e is import('./public.js').ActionFailure}
  */
 export function isActionFailure(e) {
-	return e instanceof ActionFailure;
+	return (
+		typeof e === 'object' &&
+		e !== null &&
+		Object.hasOwn(e, '_tag') &&
+		/** @type {{ _tag: string }} */ (e)._tag === 'SvelteKitActionFailure'
+	);
 }
 
 /**

packages/kit/src/exports/multi-load-test.js

@@ -0,0 +1,9 @@
+const key = '__sveltekit_module_loaded';
+// @ts-ignore
+if (globalThis[key]) {
+	console.warn(
+		'SvelteKit has been loaded twice. This is likely a misconfiguration, and could cause subtle bugs. For more information, visit https://svelte.dev/docs/kit/faq#Why-is-SvelteKit-being-loaded-twice'
+	);
+}
+// @ts-ignore
+globalThis[key] = true;

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

@@ -2,6 +2,7 @@ import { createReadStream } from 'node:fs';
 import { Readable } from 'node:stream';
 import * as set_cookie_parser from 'set-cookie-parser';
 import { SvelteKitError } from '../../runtime/control.js';
+import '../multi-load-test.js';
 
 /**
  * @param {import('http').IncomingMessage} req

packages/kit/src/exports/node/polyfills.js

@@ -1,5 +1,6 @@
 import buffer from 'node:buffer';
 import { webcrypto as crypto } from 'node:crypto';
+import '../multi-load-test.js';
 
 // `buffer.File` was added in Node 18.13.0 while the `File` global was added in Node 20.0.0
 const File = /** @type {import('node:buffer') & { File?: File}} */ (buffer).File;

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

@@ -36,7 +36,7 @@ import {
 } from './module_ids.js';
 import { import_peer } from '../../utils/import.js';
 import { compact } from '../../utils/array.js';
-import { crawlFrameworkPkgs } from 'vitefu';
+import '../multi-load-test.js';
 
 const cwd = process.cwd();
 
@@ -229,7 +229,7 @@ async function kit({ svelte_config }) {
 		 * Build the SvelteKit-provided Vite config to be merged with the user's vite.config.js file.
 		 * @see https://vitejs.dev/guide/api-plugin.html#config
 		 */
-		async config(config, config_env) {
+		config(config, config_env) {
 			initial_config = config;
 			vite_config_env = config_env;
 			is_build = config_env.command === 'build';
@@ -252,20 +252,6 @@ async function kit({ svelte_config }) {
 
 			const generated = path.posix.join(kit.outDir, 'generated');
 
-			const packages_depending_on_svelte_kit = (
-				await crawlFrameworkPkgs({
-					root: cwd,
-					isBuild: is_build,
-					viteUserConfig: config,
-					isSemiFrameworkPkgByJson: (pkg_json) => {
-						return (
-							!!pkg_json.dependencies?.['@sveltejs/kit'] ||
-							!!pkg_json.peerDependencies?.['@sveltejs/kit']
-						);
-					}
-				})
-			).ssr.noExternal;
-
 			// dev and preview config can be shared
 			/** @type {import('vite').UserConfig} */
 			const new_config = {
@@ -322,11 +308,9 @@ async function kit({ svelte_config }) {
 						//    when it is detected to keep our virtual modules working.
 						//    See https://github.com/sveltejs/kit/pull/9172
 						//    and https://vitest.dev/config/#deps-registernodeloader
-						'@sveltejs/kit',
-						// We need to bundle any packages depending on @sveltejs/kit so that
-						// everyone uses the same instances of classes such as `Redirect`
-						// which we use in `instanceof` checks
-						...packages_depending_on_svelte_kit
+						'@sveltejs/kit'
+						// Don't bundle packages that depend on `@sveltejs/kit` because they
+						// may include CJS syntax/dependencies
 					]
 				}
 			};

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

@@ -35,12 +35,13 @@ import {
 } from './constants.js';
 import { validate_page_exports } from '../../utils/exports.js';
 import { compact } from '../../utils/array.js';
-import { HttpError, Redirect, SvelteKitError } from '../control.js';
+import { HttpError, SvelteKitError } from '../control.js';
 import { INVALIDATED_PARAM, TRAILING_SLASH_PARAM, validate_depends } from '../shared.js';
 import { get_message, get_status } from '../../utils/error.js';
 import { writable } from 'svelte/store';
 import { page, update, navigating } from './state.svelte.js';
 import { add_data_suffix, add_resolution_suffix } from '../pathname.js';
+import { isRedirect } from '../../exports/index.js';
 
 export { load_css };
 
@@ -1049,7 +1050,7 @@ async function load_route({ id, invalidating, url, params, route, preload }) {
 			try {
 				branch.push(await branch_promises[i]);
 			} catch (err) {
-				if (err instanceof Redirect) {
+				if (isRedirect(err)) {
 					return {
 						type: 'redirect',
 						location: err.location
@@ -1219,7 +1220,7 @@ async function load_root_error_page({ status, error, url, route }) {
 			route: null
 		});
 	} catch (error) {
-		if (error instanceof Redirect) {
+		if (isRedirect(error)) {
 			return _goto(new URL(error.location, location.href), {}, 0);
 		}
 
@@ -2641,7 +2642,7 @@ async function _hydrate(
 			route: parsed_route ?? null
 		});
 	} catch (error) {
-		if (error instanceof Redirect) {
+		if (isRedirect(error)) {
 			// this is a real edge case — `load` would need to return
 			// a redirect but only in the browser
 			await native_navigation(new URL(error.location, location.href));

packages/kit/src/runtime/control.js

@@ -1,4 +1,8 @@
 export class HttpError {
+	/** @private */
+	// @ts-ignore this property is checked by the `isHttpError` helper
+	_tag = 'SvelteKitHttpError';
+
 	/**
 	 * @param {number} status
 	 * @param {{message: string} extends App.Error ? (App.Error | string | undefined) : App.Error} body
@@ -20,6 +24,10 @@ export class HttpError {
 }
 
 export class Redirect {
+	/** @private */
+	// @ts-ignore this property is checked by the `isRedirect` helper
+	_tag = 'SvelteKitRedirect';
+
 	/**
 	 * @param {300 | 301 | 302 | 303 | 304 | 305 | 306 | 307 | 308} status
 	 * @param {string} location
@@ -52,6 +60,10 @@ export class SvelteKitError extends Error {
  * @template {Record<string, unknown> | undefined} [T=undefined]
  */
 export class ActionFailure {
+	/** @private */
+	// @ts-ignore this property is checked by the `isActionFailure` helper
+	_tag = 'SvelteKitActionFailure';
+
 	/**
 	 * @param {number} status
 	 * @param {T} data

packages/kit/src/runtime/server/data/index.js

@@ -1,10 +1,11 @@
-import { HttpError, SvelteKitError, Redirect } from '../../control.js';
+/** @import { Redirect } from '../../control.js'; */
+import { HttpError, SvelteKitError } from '../../control.js';
 import { normalize_error } from '../../../utils/error.js';
 import { once } from '../../../utils/functions.js';
 import { load_server_data } from '../page/load_data.js';
 import { clarify_devalue_error, handle_error_and_jsonify, serialize_uses } from '../utils.js';
 import { normalize_path } from '../../../utils/url.js';
-import { text } from '../../../exports/index.js';
+import { isRedirect, text } from '../../../exports/index.js';
 import * as devalue from 'devalue';
 import { create_async_iterator } from '../../../utils/streaming.js';
 
@@ -99,7 +100,7 @@ export async function render_data(
 		const nodes = await Promise.all(
 			promises.map((p, i) =>
 				p.catch(async (error) => {
-					if (error instanceof Redirect) {
+					if (isRedirect(error)) {
 						throw error;
 					}
 
@@ -150,7 +151,7 @@ export async function render_data(
 	} catch (e) {
 		const error = normalize_error(e);
 
-		if (error instanceof Redirect) {
+		if (isRedirect(error)) {
 			return redirect_json_response(error);
 		} else {
 			return json_response(await handle_error_and_jsonify(event, options, error), 500);

packages/kit/src/runtime/server/endpoint.js

@@ -1,7 +1,7 @@
 import { ENDPOINT_METHODS, PAGE_METHODS } from '../../constants.js';
+import { isRedirect } from '../../exports/index.js';
 import { negotiate } from '../../utils/http.js';
 import { with_event } from '../app/server/event.js';
-import { Redirect } from '../control.js';
 import { method_not_allowed } from './utils.js';
 
 /**
@@ -77,7 +77,7 @@ export async function render_endpoint(event, mod, state) {
 
 		return response;
 	} catch (e) {
-		if (e instanceof Redirect) {
+		if (isRedirect(e)) {
 			return new Response(undefined, {
 				status: e.status,
 				headers: { location: e.location }

packages/kit/src/runtime/server/page/actions.js

@@ -1,9 +1,10 @@
+/** @import { HttpError } from '../../control.js'; */
 import * as devalue from 'devalue';
 import { DEV } from 'esm-env';
-import { json } from '../../../exports/index.js';
+import { isActionFailure, isRedirect, json } from '../../../exports/index.js';
 import { get_status, normalize_error } from '../../../utils/error.js';
 import { is_form_content_type, negotiate } from '../../../utils/http.js';
-import { HttpError, Redirect, ActionFailure, SvelteKitError } from '../../control.js';
+import { SvelteKitError } from '../../control.js';
 import { handle_error_and_jsonify } from '../utils.js';
 import { with_event } from '../../app/server/event.js';
 
@@ -53,11 +54,7 @@ export async function handle_action_json_request(event, options, server) {
 	try {
 		const data = await call_action(event, actions);
 
-		if (__SVELTEKIT_DEV__) {
-			validate_action_return(data);
-		}
-
-		if (data instanceof ActionFailure) {
+		if (isActionFailure(data)) {
 			return action_json({
 				type: 'failure',
 				status: data.status,
@@ -85,7 +82,7 @@ export async function handle_action_json_request(event, options, server) {
 	} catch (e) {
 		const err = normalize_error(e);
 
-		if (err instanceof Redirect) {
+		if (isRedirect(err)) {
 			return action_json_redirect(err);
 		}
 
@@ -105,9 +102,7 @@ export async function handle_action_json_request(event, options, server) {
  * @param {HttpError | Error} error
  */
 function check_incorrect_fail_use(error) {
-	return error instanceof ActionFailure
-		? new Error('Cannot "throw fail()". Use "return fail()"')
-		: error;
+	return isActionFailure(error) ? new Error('Cannot "throw fail()". Use "return fail()"') : error;
 }
 
 /**
@@ -166,11 +161,7 @@ export async function handle_action_request(event, server) {
 	try {
 		const data = await call_action(event, actions);
 
-		if (__SVELTEKIT_DEV__) {
-			validate_action_return(data);
-		}
-
-		if (data instanceof ActionFailure) {
+		if (isActionFailure(data)) {
 			return {
 				type: 'failure',
 				status: data.status,
@@ -187,7 +178,7 @@ export async function handle_action_request(event, server) {
 	} catch (e) {
 		const err = normalize_error(e);
 
-		if (err instanceof Redirect) {
+		if (isRedirect(err)) {
 			return {
 				type: 'redirect',
 				status: err.status,
@@ -250,17 +241,6 @@ async function call_action(event, actions) {
 	return with_event(event, () => action(event));
 }
 
-/** @param {any} data */
-function validate_action_return(data) {
-	if (data instanceof Redirect) {
-		throw new Error('Cannot `return redirect(...)` — use `redirect(...)` instead');
-	}
-
-	if (data instanceof HttpError) {
-		throw new Error('Cannot `return error(...)` — use `error(...)` or `return fail(...)` instead');
-	}
-}
-
 /**
  * Try to `devalue.uneval` the data object, and if it fails, return a proper Error with context
  * @param {any} data

packages/kit/src/runtime/server/page/index.js

@@ -1,8 +1,7 @@
-import { text } from '../../../exports/index.js';
+import { isRedirect, text } from '../../../exports/index.js';
 import { compact } from '../../../utils/array.js';
 import { get_status, normalize_error } from '../../../utils/error.js';
 import { add_data_suffix } from '../../pathname.js';
-import { Redirect } from '../../control.js';
 import { redirect_response, static_error_page, handle_error_and_jsonify } from '../utils.js';
 import {
 	handle_action_json_request,
@@ -219,7 +218,7 @@ export async function render_page(event, page, options, manifest, state, nodes,
 				} catch (e) {
 					const err = normalize_error(e);
 
-					if (err instanceof Redirect) {
+					if (isRedirect(err)) {
 						if (state.prerendering && should_prerender_data) {
 							const body = JSON.stringify({
 								type: 'redirect',