WIP

packages/svelte/src/compiler/phases/1-parse/acorn.js

@@ -92,6 +92,13 @@ export function parse_expression_at(parser, source, index) {
 
 		add_comments(ast);
 
+		let end = ast.end;
+
+		const last_comment = parser.root.comments.at(-1);
+		if (last_comment && last_comment.end > end) end = last_comment.end;
+
+		parser.index = end;
+
 		return ast;
 	} catch (e) {
 		handle_parse_error(e);

packages/svelte/src/compiler/phases/1-parse/read/context.js

@@ -60,6 +60,8 @@ export default function read_pattern(parser) {
 		expression.end = expression.typeAnnotation.end;
 	}
 
+	parser.index = expression.end;
+
 	return expression;
 }
 

packages/svelte/src/compiler/phases/1-parse/read/expression.js

@@ -36,13 +36,6 @@ export default function read_expression(parser, opening_token, disallow_loose) {
 	try {
 		const node = parse_expression_at(parser, parser.template, parser.index);
 
-		let index = /** @type {number} */ (node.end);
-
-		const last_comment = parser.root.comments.at(-1);
-		if (last_comment && last_comment.end > index) index = last_comment.end;
-
-		parser.index = index;
-
 		return /** @type {Expression} */ (remove_parens(node));
 	} catch (err) {
 		// If we are in an each loop we need the error to be thrown in cases like

packages/svelte/src/compiler/phases/1-parse/state/tag.js

@@ -387,14 +387,20 @@ function open(parser) {
 			parser.eat(')', true);
 		}
 
-		const prelude = parser.template.slice(0, params_start).replace(/\S/g, ' ');
-		const params = parser.template.slice(params_start, parser.index);
+		/** @type {Pattern[]} */
+		let params = [];
 
-		let function_expression = matched
-			? /** @type {ArrowFunctionExpression} */ (
-					parse_expression_at(parser, prelude + `${params} => {}`, params_start)
-				)
-			: { params: [] };
+		if (matched) {
+			const prelude = parser.template.slice(0, params_start).replace(/\S/g, ' ');
+			const params_string = parser.template.slice(params_start, parser.index);
+
+			const fn = /** @type {ArrowFunctionExpression} */ (
+				parse_expression_at(parser, prelude + `${params_string} => {}`, params_start)
+			);
+
+			params = fn.params;
+			parser.index -= 6;
+		}
 
 		parser.allow_whitespace();
 		parser.eat('}', true);
@@ -406,7 +412,7 @@ function open(parser) {
 			end: -1,
 			expression: id,
 			typeParams: type_params,
-			parameters: function_expression.params,
+			parameters: params,
 			body: create_fragment(),
 			metadata: {
 				can_hoist: false,