fix: svelte 5 prop types (#14934)

Author: antonyfaris

.changeset/olive-lands-try.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/svelte': patch
+---
+
+Fixes an issue where Svelte 5 components used in Astro files would not have proper type checking and IntelliSense.

packages/integrations/svelte/package.json

@@ -24,10 +24,12 @@
     "./editor": "./dist/editor.cjs",
     "./client.js": "./dist/client.svelte.js",
     "./server.js": "./dist/server.js",
+    "./svelte-shims.d.ts": "./svelte-shims.d.ts",
     "./package.json": "./package.json"
   },
   "files": [
-    "dist"
+    "dist",
+    "svelte-shims.d.ts"
   ],
   "scripts": {
     "build": "astro-scripts build \"src/**/*.ts\" && astro-scripts build \"src/editor.cts\" --force-cjs --no-clean-dist && tsc",

packages/integrations/svelte/src/editor.cts

@@ -7,12 +7,22 @@ export function toTSX(code: string, className: string): string {
 	`;
 
 	try {
-		let tsx = svelte2tsx(code, { mode: 'ts' }).code;
-		tsx = '/// <reference types="svelte2tsx/svelte-shims" />\n' + tsx;
-		result = tsx.replace(
-			'export default class extends __sveltets_2_createSvelte2TsxComponent(',
-			`export default function ${className}__AstroComponent_(_props: typeof Component.props): any {}\nlet Component = `,
-		);
+		let tsx = svelte2tsx(code, { mode: 'ts', isTsFile: true }).code;
+		tsx = "import '@astrojs/svelte/svelte-shims.d.ts';\n" + tsx;
+
+		// New svelte2tsx output (Svelte 5)
+		if (tsx.includes('export default $$Component;')) {
+			result = tsx.replace(
+				'export default $$Component;',
+				`export default function ${className}__AstroComponent_(_props: import('svelte').ComponentProps<typeof $$$$Component>): any {}`,
+			);
+		} else {
+			// Old svelte2tsx output
+			result = tsx.replace(
+				'export default class extends __sveltets_2_createSvelte2TsxComponent(',
+				`export default function ${className}__AstroComponent_(_props: typeof Component.props): any {}\nlet Component = `,
+			);
+		}
 	} catch {
 		return result;
 	}

packages/integrations/svelte/svelte-shims.d.ts

@@ -0,0 +1 @@
+import 'svelte2tsx/svelte-shims-v4';

packages/integrations/svelte/test/check.test.js

@@ -0,0 +1,18 @@
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+import { fileURLToPath } from 'node:url';
+import { cli } from '../../../astro/test/test-utils.js';
+
+describe('Svelte Check', () => {
+	it('should fail check on type error', async () => {
+		const root = fileURLToPath(new URL('./fixtures/prop-types/', import.meta.url));
+		const { getResult } = cli('check', '--root', root);
+		const { exitCode, stdout } = await getResult();
+
+		assert.equal(exitCode, 1, 'Expected check to fail (exit code 1)');
+		assert.ok(
+			stdout.includes(`Type 'string' is not assignable to type 'number'`),
+			'Expected specific type error message',
+		);
+	});
+});

packages/integrations/svelte/test/fixtures/async-rendering/src/components/PropTypes.svelte

@@ -0,0 +1,13 @@
+<script lang="ts">
+  interface Props {
+    name: string;
+    age?: number;
+    bold?: boolean;
+  }
+
+  let { name, age = 0, bold = false }: Props = $props();
+</script>
+
+<p class:bold={bold}>
+  Hello {name}, you are {age} years old.
+</p>

packages/integrations/svelte/test/fixtures/async-rendering/tsconfig.json

@@ -0,0 +1,5 @@
+{
+  "extends": "astro/tsconfigs/strict",
+  "include": [".astro/types.d.ts", "**/*"],
+  "exclude": ["dist"]
+}

packages/integrations/svelte/test/fixtures/prop-types/astro.config.mjs

@@ -0,0 +1,7 @@
+import { defineConfig } from 'astro/config';
+import svelte from '@astrojs/svelte';
+
+export default defineConfig({
+  srcDir: './types',
+  integrations: [svelte()]
+});

packages/integrations/svelte/test/fixtures/prop-types/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "svelte-prop-types",
+  "type": "module",
+  "version": "0.0.1",
+  "scripts": {
+    "dev": "astro dev",
+    "build": "astro build",
+    "preview": "astro preview",
+    "astro": "astro"
+  },
+  "dependencies": {
+    "@astrojs/svelte": "^7.2.2",
+    "astro": "^5.16.0",
+    "svelte": "^5.43.14"
+  }
+}

packages/integrations/svelte/test/fixtures/prop-types/svelte.config.js

@@ -0,0 +1 @@
+export default {};