feat: add Svelte 4 migration

.changeset/lucky-coins-hunt.md

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+---
+'svelte-migrate': minor
+---
+
+feat: add Svelte 4 migration

packages/migrate/migrations/svelte-4/index.js

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+import colors from 'kleur';
+import fs from 'node:fs';
+import prompts from 'prompts';
+import glob from 'tiny-glob/sync.js';
+import { bail, check_git } from '../../utils.js';
+import { update_js_file, update_svelte_file } from './migrate.js';
+
+export async function migrate() {
+	if (!fs.existsSync('package.json')) {
+		bail('Please re-run this script in a directory with a package.json');
+	}
+
+	console.log(colors.bold().yellow('\nThis will update files in the current directory\n'));
+
+	const use_git = check_git();
+
+	const response = await prompts({
+		type: 'confirm',
+		name: 'value',
+		message: 'Continue?',
+		initial: false
+	});
+
+	if (!response.value) {
+		process.exit(1);
+	}
+
+	// const { default: config } = fs.existsSync('svelte.config.js')
+	// 	? await import(pathToFileURL(path.resolve('svelte.config.js')).href)
+	// 	: { default: {} };
+
+	/** @type {string[]} */
+	const svelte_extensions = /* config.extensions ?? - disabled because it would break .svx */ ['.svelte'];
+	const extensions = [...svelte_extensions, '.ts', '.js'];
+	// TODO read tsconfig/jsconfig if available? src/** will be good for 99% of cases
+	const files = glob('src/**', { filesOnly: true, dot: true }).map((file) =>
+		file.replace(/\\/g, '/')
+	);
+
+	for (const file of files) {
+		if (extensions.some((ext) => file.endsWith(ext))) {
+			if (svelte_extensions.some((ext) => file.endsWith(ext))) {
+				update_svelte_file(file);
+			} else {
+				update_js_file(file);
+			}
+		}
+	}
+
+	console.log(colors.bold().green('✔ Your project has been migrated'));
+
+	console.log('\nRecommended next steps:\n');
+
+	const cyan = colors.bold().cyan;
+
+	const tasks = [
+		use_git && cyan('git commit -m "migration to Svelte 4"'),
+		'Review the migration guide at TODO',
+		'Read the updated docs at https://svelte.dev/docs'
+	].filter(Boolean);
+
+	tasks.forEach((task, i) => {
+		console.log(`  ${i + 1}: ${task}`);
+	});
+
+	console.log('');
+
+	if (use_git) {
+		console.log(`Run ${cyan('git diff')} to review changes.\n`);
+	}
+}

packages/migrate/migrations/svelte-4/migrate.js

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+import fs from 'node:fs';
+import { Project, ts, Node } from 'ts-morph';
+
+/** @param {string} file_path */
+export function update_svelte_file(file_path) {
+	const content = fs.readFileSync(file_path, 'utf-8');
+	const updated = content.replace(
+		/<script([^]*?)>([^]+?)<\/script>(\n*)/g,
+		(_match, attrs, contents, whitespace) => {
+			return `<script${attrs}>${transform_code(contents)}</script>${whitespace}`;
+		}
+	);
+	fs.writeFileSync(file_path, transform_svelte_code(updated), 'utf-8');
+}
+
+/** @param {string} file_path */
+export function update_js_file(file_path) {
+	const content = fs.readFileSync(file_path, 'utf-8');
+	const updated = transform_code(content);
+	fs.writeFileSync(file_path, updated, 'utf-8');
+}
+
+/** @param {string} code */
+export function transform_code(code) {
+	const project = new Project({ useInMemoryFileSystem: true });
+	const source = project.createSourceFile('svelte.ts', code);
+	update_imports(source);
+	update_typeof_svelte_component(source);
+	update_action_types(source);
+	update_action_return_types(source);
+	return source.getFullText();
+}
+
+/** @param {string} code */
+export function transform_svelte_code(code) {
+	return update_transitions(update_svelte_options(code));
+}
+
+/**
+ * <svelte:options tag=".." /> -> <svelte:options customElement=".." />
+ * @param {string} code
+ */
+function update_svelte_options(code) {
+	return code.replace(/<svelte:options([^]*?)\stag=([^]*?)\/?>/, (match) => {
+		return match.replace('tag=', 'customElement=');
+	});
+}
+
+/**
+ * transition/in/out:x -> transition/in/out:x|global
+ * @param {string} code
+ */
+function update_transitions(code) {
+	return code.replace(/(\s)(transition:|in:|out:)(\w+)(?=[\s>=])/g, '$1$2$3|global');
+}
+
+/**
+ * Action<T> -> Action<T, any>
+ * @param {import('ts-morph').SourceFile} source
+ */
+function update_action_types(source) {
+	const imports = get_imports(source, 'svelte/action', 'Action');
+	for (const namedImport of imports) {
+		const identifiers = find_identifiers(source, namedImport.getAliasNode()?.getText() ?? 'Action');
+		for (const id of identifiers) {
+			const parent = id.getParent();
+			if (Node.isTypeReference(parent)) {
+				const type_args = parent.getTypeArguments();
+				if (type_args.length === 1) {
+					parent.addTypeArgument('any');
+				} else if (type_args.length === 0) {
+					parent.addTypeArgument('HTMLElement');
+					parent.addTypeArgument('any');
+				}
+			}
+		}
+	}
+}
+
+/**
+ * ActionReturn -> ActionReturn<any>
+ * @param {import('ts-morph').SourceFile} source
+ */
+function update_action_return_types(source) {
+	const imports = get_imports(source, 'svelte/action', 'ActionReturn');
+	for (const namedImport of imports) {
+		const identifiers = find_identifiers(
+			source,
+			namedImport.getAliasNode()?.getText() ?? 'ActionReturn'
+		);
+		for (const id of identifiers) {
+			const parent = id.getParent();
+			if (Node.isTypeReference(parent)) {
+				const type_args = parent.getTypeArguments();
+				if (type_args.length === 0) {
+					parent.addTypeArgument('any');
+				}
+			}
+		}
+	}
+}
+
+/**
+ * SvelteComponentTyped -> SvelteComponent
+ * @param {import('ts-morph').SourceFile} source
+ */
+function update_imports(source) {
+	const identifiers = find_identifiers(source, 'SvelteComponent');
+	const can_rename = identifiers.every((id) => {
+		const parent = id.getParent();
+		return (
+			(Node.isImportSpecifier(parent) &&
+				!parent.getAliasNode() &&
+				parent.getParent().getParent().getParent().getModuleSpecifier().getText() === 'svelte') ||
+			!is_declaration(parent)
+		);
+	});
+
+	const imports = get_imports(source, 'svelte', 'SvelteComponentTyped');
+	for (const namedImport of imports) {
+		if (can_rename) {
+			namedImport.renameAlias('SvelteComponent');
+			if (
+				namedImport
+					.getParent()
+					.getElements()
+					.some((e) => !e.getAliasNode() && e.getNameNode().getText() === 'SvelteComponent')
+			) {
+				namedImport.remove();
+			} else {
+				namedImport.setName('SvelteComponent');
+				namedImport.removeAlias();
+			}
+		} else {
+			namedImport.renameAlias('SvelteComponentTyped');
+			namedImport.setName('SvelteComponent');
+		}
+	}
+}
+
+/**
+ * typeof SvelteComponent -> typeof SvelteComponent<any>
+ * @param {import('ts-morph').SourceFile} source
+ */
+function update_typeof_svelte_component(source) {
+	const imports = get_imports(source, 'svelte', 'SvelteComponent');
+
+	for (const type of imports) {
+		if (type) {
+			const name = type.getAliasNode() ?? type.getNameNode();
+			name.findReferencesAsNodes().forEach((ref) => {
+				const parent = ref.getParent();
+				if (parent && Node.isTypeQuery(parent)) {
+					const id = parent.getFirstChildByKind(ts.SyntaxKind.Identifier);
+					if (id?.getText() === name.getText()) {
+						const typeArguments = parent.getTypeArguments();
+						if (typeArguments.length === 0) {
+							parent.addTypeArgument('any');
+						}
+					}
+				}
+			});
+		}
+	}
+}
+
+/**
+ * @param {import('ts-morph').SourceFile} source
+ * @param {string} from
+ * @param {string} name
+ */
+function get_imports(source, from, name) {
+	return source
+		.getImportDeclarations()
+		.filter((i) => i.getModuleSpecifierValue() === from)
+		.flatMap((i) => i.getNamedImports())
+		.filter((i) => i.getName() === name);
+}
+
+/**
+ * @param {import('ts-morph').SourceFile} source
+ * @param {string} name
+ */
+function find_identifiers(source, name) {
+	return source.getDescendantsOfKind(ts.SyntaxKind.Identifier).filter((i) => i.getText() === name);
+}
+
+/**
+ * Does not include imports
+ * @param {Node} node
+ */
+function is_declaration(node) {
+	return (
+		Node.isVariableDeclaration(node) ||
+		Node.isFunctionDeclaration(node) ||
+		Node.isClassDeclaration(node) ||
+		Node.isTypeAliasDeclaration(node) ||
+		Node.isInterfaceDeclaration(node)
+	);
+}