allow leading and trailing comments in mustache tags

Author: BlueGreenMagick

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

@@ -29,6 +29,7 @@ export function parse(source, typescript) {
  * @param {string} source
  * @param {boolean} typescript
  * @param {number} index
+ * @returns {acorn.Expression & { leadingComments?: CommentWithLocation[]; trailingComments?: CommentWithLocation[]; }}
  */
 export function parse_expression_at(source, typescript, index) {
 	const parser = typescript ? ParserWithTS : acorn.Parser;
@@ -110,6 +111,9 @@ function get_comment_handlers(source) {
 					}
 				}
 			});
+			if (comments.length > 0) {
+				(ast.trailingComments ||= []).push(...comments.splice(0))
+			}
 		}
 	};
 }

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

@@ -17,6 +17,10 @@ export default function read_expression(parser) {
 		}
 
 		let index = /** @type {number} */ (node.end);
+		if (node.trailingComments !== undefined && node.trailingComments.length > 0) {
+			index = node.trailingComments.at(-1).end;
+		}
+
 		while (num_parens > 0) {
 			const char = parser.template[index];
 

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

@@ -14,9 +14,14 @@ export default function mustache(parser) {
 	parser.allow_whitespace();
 
 	if (parser.eat('#')) return open(parser);
-	if (parser.eat('/')) return close(parser);
 	if (parser.eat(':')) return next(parser);
 	if (parser.eat('@')) return special(parser);
+	if (parser.match('/')) {
+		if (!parser.match('/*') && !parser.match('//')) {
+			parser.eat('/');
+			return close(parser);
+		}
+	}
 
 	const expression = read_expression(parser);