breaking: remove baseUrl fallback from generated tsconfig

- don't generate baseUrl anymore and don't adjust paths anymore depending on whether or not the user has paths in their tsconfig.json
- more strict validation: warn on baseUrl/paths and suggest kit.alias instead

closes #11286

.changeset/dull-eyes-check.md

@@ -0,0 +1,5 @@
+---
+"@sveltejs/kit": major
+---
+
+breaking: remove baseUrl fallback from generated tsconfig

.changeset/loud-parrots-flow.md

@@ -0,0 +1,5 @@
+---
+"svelte-migrate": minor
+---
+
+feat: add sveltekit v2 migration

documentation/docs/60-appendix/30-migrating-to-sveltekit-2.md

@@ -123,6 +123,10 @@ In SvelteKit 1, those properties included `form` and `data`. These were deprecat
 
 If a form contains an `<input type="file">` but does not have an `enctype="multipart/form-data"` attribute, non-JS submissions will omit the file. SvelteKit 2 will throw an error if it encounters a form like this during a `use:enhance` submission to ensure that your forms work correctly when JavaScript is not present.
 
+## Generated `tsconfig.json` is more strict
+
+Previously, the generated `tsconfig.json` was trying its best to still produce a somewhat valid config when your `tsconfig.json` included `paths` or `baseUrl`. In SvelteKit 2, the validation is more strict and will warn when you use either `paths` or `baseUrl` in your `tsconfig.json`. These settings are used to generate path aliases and you should use [the `alias` config](configuration#alias) option in your `svelte.config.js` instead, to also create a corresponding alias for the bundler.
+
 ## Updated dependency requirements
 
 SvelteKit 2 requires Node `18.13` or higher, and the following minimum dependency versions:

packages/kit/src/core/sync/write_tsconfig.js

@@ -43,44 +43,14 @@ export function write_tsconfig(kit, cwd = process.cwd()) {
 	const user_config = load_user_tsconfig(cwd);
 	if (user_config) validate_user_config(kit, cwd, out, user_config);
 
-	// only specify baseUrl if a) the user doesn't specify their own baseUrl
-	// and b) they have non-relative paths. this causes problems with auto-imports,
-	// so we print a suggestion that they use relative paths instead
-	// TODO(v2): never include base URL, and skip the check below
-	let include_base_url = false;
-
-	if (user_config && !user_config.options.compilerOptions?.baseUrl) {
-		const non_relative_paths = new Set();
-		for (const paths of Object.values(user_config?.options.compilerOptions?.paths || {})) {
-			for (const path of paths) {
-				if (!path.startsWith('.')) non_relative_paths.add(path);
-			}
-		}
-
-		if (non_relative_paths.size) {
-			include_base_url = true;
-
-			console.log(colors.bold().yellow('Please replace non-relative compilerOptions.paths:\n'));
-
-			for (const path of non_relative_paths) {
-				console.log(`  - "${path}" -> "./${path}"`);
-			}
-
-			console.log(
-				'\nDoing so allows us to omit "baseUrl" — which causes problems with imports — from the generated tsconfig.json. See https://github.com/sveltejs/kit/pull/8437 for more information.'
-			);
-		}
-	}
-
-	write_if_changed(out, JSON.stringify(get_tsconfig(kit, include_base_url), null, '\t'));
+	write_if_changed(out, JSON.stringify(get_tsconfig(kit), null, '\t'));
 }
 
 /**
  * Generates the tsconfig that the user's tsconfig inherits from.
  * @param {import('types').ValidatedKitConfig} kit
- * @param {boolean} include_base_url
  */
-export function get_tsconfig(kit, include_base_url) {
+export function get_tsconfig(kit) {
 	/** @param {string} file */
 	const config_relative = (file) => posixify(path.relative(kit.outDir, file));
 
@@ -122,8 +92,7 @@ export function get_tsconfig(kit, include_base_url) {
 	const config = {
 		compilerOptions: {
 			// generated options
-			baseUrl: include_base_url ? config_relative('.') : undefined,
-			paths: get_tsconfig_paths(kit, include_base_url),
+			paths: get_tsconfig_paths(kit),
 			rootDirs: [config_relative('.'), './types'],
 
 			// essential options
@@ -184,29 +153,17 @@ function validate_user_config(kit, cwd, out, config) {
 	const options = config.options.compilerOptions || {};
 
 	if (extends_framework_config) {
-		const { paths: user_paths } = options;
-
-		if (user_paths && fs.existsSync(kit.files.lib)) {
-			/** @type {string[]} */
-			const lib = user_paths['$lib'] || [];
-			/** @type {string[]} */
-			const lib_ = user_paths['$lib/*'] || [];
-
-			// TODO(v2): check needs to be adjusted when we remove the base path
-			const missing_lib_paths =
-				!lib.some((relative) => path.resolve(cwd, relative) === kit.files.lib) ||
-				!lib_.some((relative) => path.resolve(cwd, relative) === path.join(kit.files.lib, '/*'));
-
-			if (missing_lib_paths) {
-				console.warn(
-					colors
-						.bold()
-						.yellow(`Your compilerOptions.paths in ${config.kind} should include the following:`)
-				);
-				let relative = posixify(path.relative('.', kit.files.lib));
-				if (!relative.startsWith('.')) relative = `./${relative}`;
-				console.warn(`{\n  "$lib":["${relative}"],\n  "$lib/*":["${relative}/*"]\n}`);
-			}
+		const { paths, baseUrl } = options;
+
+		if (baseUrl || paths) {
+			console.warn(
+				colors
+					.bold()
+					.yellow(
+						"You have specified a baseUrl and/or paths in your tsconfig.json which interferes with SvelteKit's auto-generated tsconfig.json. " +
+							'Remove it to avoid problems with intellisense. For path aliases, use `kit.alias` instead: https://kit.svelte.dev/docs/configuration#alias'
+					)
+			);
 		}
 	} else {
 		let relative = posixify(path.relative('.', out));
@@ -231,9 +188,8 @@ const value_regex = /^(.*?)((\/\*)|(\.\w+))?$/;
  * Related to vite alias creation.
  *
  * @param {import('types').ValidatedKitConfig} config
- * @param {boolean} include_base_url
  */
-function get_tsconfig_paths(config, include_base_url) {
+function get_tsconfig_paths(config) {
 	/** @param {string} file */
 	const config_relative = (file) => posixify(path.relative(config.outDir, file));
 
@@ -252,9 +208,7 @@ function get_tsconfig_paths(config, include_base_url) {
 		const value_match = value_regex.exec(value);
 		if (!value_match) throw new Error(`Invalid alias value: ${value}`);
 
-		const rel_path = (include_base_url ? project_relative : config_relative)(
-			remove_trailing_slashstar(value)
-		);
+		const rel_path = config_relative(remove_trailing_slashstar(value));
 		const slashstar = key_match[2];
 
 		if (slashstar) {

packages/kit/src/core/sync/write_tsconfig.spec.js

@@ -14,7 +14,7 @@ test('Creates tsconfig path aliases from kit.alias', () => {
 		}
 	});
 
-	const { compilerOptions } = get_tsconfig(kit, false);
+	const { compilerOptions } = get_tsconfig(kit);
 
 	// $lib isn't part of the outcome because there's a "path exists"
 	// check in the implementation
@@ -27,31 +27,6 @@ test('Creates tsconfig path aliases from kit.alias', () => {
 	});
 });
 
-test('Creates tsconfig path aliases from kit.alias with existing baseUrl', () => {
-	const { kit } = validate_config({
-		kit: {
-			alias: {
-				simpleKey: 'simple/value',
-				key: 'value',
-				'key/*': 'some/other/value/*',
-				keyToFile: 'path/to/file.ts'
-			}
-		}
-	});
-
-	const { compilerOptions } = get_tsconfig(kit, true);
-
-	// $lib isn't part of the outcome because there's a "path exists"
-	// check in the implementation
-	expect(compilerOptions.paths).toEqual({
-		simpleKey: ['simple/value'],
-		'simpleKey/*': ['simple/value/*'],
-		key: ['value'],
-		'key/*': ['some/other/value/*'],
-		keyToFile: ['path/to/file.ts']
-	});
-});
-
 test('Allows generated tsconfig to be mutated', () => {
 	const { kit } = validate_config({
 		kit: {
@@ -63,7 +38,7 @@ test('Allows generated tsconfig to be mutated', () => {
 		}
 	});
 
-	const config = get_tsconfig(kit, false);
+	const config = get_tsconfig(kit);
 
 	// @ts-expect-error
 	assert.equal(config.extends, 'some/other/tsconfig.json');
@@ -81,7 +56,7 @@ test('Allows generated tsconfig to be replaced', () => {
 		}
 	});
 
-	const config = get_tsconfig(kit, false);
+	const config = get_tsconfig(kit);
 
 	// @ts-expect-error
 	assert.equal(config.extends, 'some/other/tsconfig.json');
@@ -96,7 +71,7 @@ test('Creates tsconfig include from kit.files', () => {
 		}
 	});
 
-	const { include } = get_tsconfig(kit, false);
+	const { include } = get_tsconfig(kit);
 
 	expect(include).toEqual([
 		'ambient.d.ts',

packages/migrate/migrations/sveltekit-2/migrate.js

@@ -66,6 +66,12 @@ export function update_tsconfig_content(content) {
 		);
 	}
 
+	if (content.includes('"paths":') || content.includes('"baseUrl":')) {
+		log_migration(
+			'`paths` and/or `baseUrl` detected in your tsconfig.json - remove it and use `kit.alias` instead: https://kit.svelte.dev/docs/v2-migration-guide#generated-tsconfigjson-is-more-strict'
+		);
+	}
+
 	return updated;
 }