Include declarations for default template for non-ts users

packages/create-svelte/index.js

@@ -17,7 +17,7 @@ export async function create(cwd, options) {
 
 /**
  * @param {string} template
- * @param {boolean} typescript
+ * @param {false | "checkjs" | "typescript"} types
  * @param {string} name
  * @param {string} cwd
  */
@@ -40,7 +40,7 @@ function write_template_files(template, types, name, cwd) {
 }
 
 /**
- build*
+ *
  * @param {string} cwd
  * @param {import('./types/internal').Options} options
  * @param {string} name

packages/create-svelte/scripts/build-templates.js

@@ -5,21 +5,7 @@ import prettier from 'prettier';
 import { transform } from 'sucrase';
 import glob from 'tiny-glob/sync.js';
 import { mkdirp, rimraf } from '../utils.js';
-
-/** @param {string} typescript */
-function convert_typescript(typescript) {
-	const transformed = transform(typescript, {
-		transforms: ['typescript']
-	});
-
-	return prettier.format(transformed.code, {
-		parser: 'babel',
-		useTabs: true,
-		singleQuote: true,
-		trailingComma: 'none',
-		printWidth: 100
-	});
-}
+import { transpile, extract_types } from '../transformers.js';
 
 /** @param {Set<string>} shared */
 async function generate_templates(shared) {
@@ -88,7 +74,7 @@ async function generate_templates(shared) {
 			} else if (file.name.endsWith('.ts')) {
 				js.push({
 					name: file.name.replace(/\.ts$/, '.js'),
-					contents: convert_typescript(file.contents)
+					contents: transpile(file.contents)
 				});
 			} else if (file.name.endsWith('.svelte')) {
 				// we jump through some hoops, rather than just using svelte.preprocess,
@@ -143,6 +129,18 @@ async function generate_templates(shared) {
 			}
 		}
 
+		JSON.parse(fs.readFileSync(meta_file, 'utf-8')).generateDeclarationsFor?.forEach(
+			(/** @type string */ name) => {
+				if (!name.endsWith('.ts')) throw new Error(`${name} is not a .ts file`);
+
+				const filepath = path.join(cwd, name);
+				js.push({
+					name: path.normalize(name.replace(/.ts$/, '.d.ts')),
+					contents: extract_types(filepath)
+				});
+			}
+		);
+
 		fs.copyFileSync(meta_file, `${dir}/meta.json`);
 		fs.writeFileSync(`${dir}/files.ts.json`, JSON.stringify(ts, null, '\t'));
 		fs.writeFileSync(`${dir}/files.js.json`, JSON.stringify(js, null, '\t'));
@@ -190,7 +188,7 @@ async function generate_shared() {
 				name: js_name,
 				include: [...include],
 				exclude: [...exclude, 'typescript'],
-				contents: convert_typescript(contents)
+				contents: transpile(contents)
 			});
 
 			include.push('typescript');

packages/create-svelte/templates/default/.meta.json

@@ -1,3 +1,4 @@
 {
-	"description": "SvelteKit demo app"
+	"description": "SvelteKit demo app",
+	"generateDeclarationsFor": ["src/lib/form.ts"]
 }

packages/create-svelte/transformers.js

@@ -0,0 +1,47 @@
+import { transform } from 'sucrase';
+import ts from 'typescript';
+import prettier from 'prettier';
+
+/**
+ * Transpile a TypeScript source string to JavaScript.
+ * @param {string} typescript
+ */
+export function transpile(typescript) {
+	const transformed = transform(typescript, { transforms: ['typescript'] });
+
+	return prettier.format(transformed.code, {
+		parser: 'babel',
+		useTabs: true,
+		singleQuote: true,
+		trailingComma: 'none',
+		printWidth: 100
+	});
+}
+
+/**
+ * Extract type declarations from a TypeScript file.
+ * @param {string} filepath the path to the file to extract types from
+ * @returns {string}
+ */
+export function extract_types(filepath) {
+	// Create a Program with an in-memory emit
+	const host = ts.createCompilerHost({
+		declaration: true,
+		emitDeclarationOnly: true
+	});
+	let declaration;
+	host.writeFile = (_, contents) => (declaration = contents);
+
+	// Prepare and emit the d.ts files
+	const program = ts.createProgram(
+		[filepath],
+		{
+			declaration: true,
+			emitDeclarationOnly: true
+		},
+		host
+	);
+	program.emit();
+
+	return declaration;
+}