we (web engine): Experimental web browser project to understand the limits of Claude
Fix export default anonymous function/class parsing
export default function() {} and export default class {} are valid
JavaScript but the parser incorrectly required a name. Check whether
the function/class has a name and route to expression parsing when
anonymous.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
+59
-4
+59
-4
crates/js/src/parser.rs
+59
-4
crates/js/src/parser.rs
···
1222
1222
// `export default ...`
1223
1223
if self.eat(&TokenKind::Default) {
1224
1224
if matches!(self.peek_kind(), TokenKind::Function) {
1225
-
let decl = self.parse_function_declaration()?;
1225
+
// Named function → declaration, anonymous → default expression
1226
+
let has_name = matches!(self.peek_ahead(1), TokenKind::Identifier(_))
1227
+
|| (matches!(self.peek_ahead(1), TokenKind::Star)
1228
+
&& matches!(self.peek_ahead(2), TokenKind::Identifier(_)));
1229
+
if has_name {
1230
+
let decl = self.parse_function_declaration()?;
1231
+
return Ok(Stmt {
1232
+
kind: StmtKind::Export(ExportDecl::Declaration(Box::new(decl))),
1233
+
span: self.span_from(start),
1234
+
});
1235
+
}
1236
+
let expr = self.parse_function_expression()?;
1226
1237
return Ok(Stmt {
1227
-
kind: StmtKind::Export(ExportDecl::Declaration(Box::new(decl))),
1238
+
kind: StmtKind::Export(ExportDecl::Default(expr)),
1228
1239
span: self.span_from(start),
1229
1240
});
1230
1241
}
1231
1242
if matches!(self.peek_kind(), TokenKind::Class) {
1232
-
let decl = self.parse_class_declaration()?;
1243
+
// Named class → declaration, anonymous → default expression
1244
+
if matches!(self.peek_ahead(1), TokenKind::Identifier(_)) {
1245
+
let decl = self.parse_class_declaration()?;
1246
+
return Ok(Stmt {
1247
+
kind: StmtKind::Export(ExportDecl::Declaration(Box::new(decl))),
1248
+
span: self.span_from(start),
1249
+
});
1250
+
}
1251
+
let expr = self.parse_class_expression()?;
1233
1252
return Ok(Stmt {
1234
-
kind: StmtKind::Export(ExportDecl::Declaration(Box::new(decl))),
1253
+
kind: StmtKind::Export(ExportDecl::Default(expr)),
1235
1254
span: self.span_from(start),
1236
1255
});
1237
1256
}
···
3462
3481
match &prog.body[0].kind {
3463
3482
StmtKind::Export(ExportDecl::Declaration(_)) => {}
3464
3483
_ => panic!("expected export declaration"),
3484
+
}
3485
+
}
3486
+
3487
+
#[test]
3488
+
fn test_export_default_anonymous_function() {
3489
+
let prog = Parser::parse_module("export default function() {}").unwrap();
3490
+
match &prog.body[0].kind {
3491
+
StmtKind::Export(ExportDecl::Default(expr)) => {
3492
+
assert!(matches!(expr.kind, ExprKind::Function(ref def) if def.id.is_none()));
3493
+
}
3494
+
_ => panic!("expected export default anonymous function"),
3495
+
}
3496
+
}
3497
+
3498
+
#[test]
3499
+
fn test_export_default_anonymous_class() {
3500
+
let prog = Parser::parse_module("export default class {}").unwrap();
3501
+
match &prog.body[0].kind {
3502
+
StmtKind::Export(ExportDecl::Default(expr)) => {
3503
+
assert!(matches!(expr.kind, ExprKind::Class(ref def) if def.id.is_none()));
3504
+
}
3505
+
_ => panic!("expected export default anonymous class"),
3506
+
}
3507
+
}
3508
+
3509
+
#[test]
3510
+
fn test_export_default_anonymous_generator() {
3511
+
let prog = Parser::parse_module("export default function*() {}").unwrap();
3512
+
match &prog.body[0].kind {
3513
+
StmtKind::Export(ExportDecl::Default(expr)) => {
3514
+
assert!(matches!(
3515
+
expr.kind,
3516
+
ExprKind::Function(ref def) if def.id.is_none() && def.is_generator
3517
+
));
3518
+
}
3519
+
_ => panic!("expected export default anonymous generator"),
3465
3520
}
3466
3521
}
3467
3522