support legacyAst on REPL

sites/svelte-5-preview/src/lib/Output/CompilerOptions.svelte

@@ -23,6 +23,12 @@
 		<Checkbox bind:checked={$compile_options.dev} />
 		<span class="boolean">{$compile_options.dev}</span>,
 	</label>
+
+	<label class="option">
+		<span class="key">modernAst:</span>
+		<Checkbox bind:checked={$compile_options.modernAst} />
+		<span class="boolean">{$compile_options.modernAst}</span>,
+	</label>
 	});
 </div>
 

sites/svelte-5-preview/src/lib/Repl.svelte

@@ -77,7 +77,8 @@
 	/** @type {import('svelte/compiler').CompileOptions} */
 	const DEFAULT_COMPILE_OPTIONS = {
 		generate: 'client',
-		dev: false
+		dev: false,
+		modernAst: true
 	};
 
 	/** @type {Map<string, import('@codemirror/state').EditorState>} */

sites/svelte-5-preview/src/lib/workers/compiler/index.js

@@ -70,7 +70,7 @@ function compile({ id, source, options, return_ast }) {
 
 			const { js, css, warnings, metadata } = compiled;
 
-			const ast = return_ast ? svelte.parse(source, { modern: true }) : undefined;
+			const ast = return_ast ? svelte.parse(source, { modern: options.modernAst }) : undefined;
 
 			return {
 				id,