Fix parsing of `async` in for-of loops (#3745)

core/parser/src/parser/expression/assignment/mod.rs

@@ -141,15 +141,22 @@ where
                     1
                 };
 
+                let peek_1 = cursor.peek(1, interner).or_abrupt()?.kind().clone();
                 if !cursor
                     .peek_is_line_terminator(skip_n, interner)
                     .or_abrupt()?
-                    && matches!(
-                        cursor.peek(1, interner).or_abrupt()?.kind(),
+                    && (matches!(peek_1, TokenKind::Punctuator(Punctuator::OpenParen))
+                        || (matches!(
+                            peek_1,
                             TokenKind::IdentifierName(_)
-                            | TokenKind::Keyword((Keyword::Yield | Keyword::Await, _))
-                            | TokenKind::Punctuator(Punctuator::OpenParen)
-                    )
+                                | TokenKind::Keyword((
+                                    Keyword::Yield | Keyword::Await | Keyword::Of,
+                                    _
+                                ))
+                        ) && matches!(
+                            cursor.peek(2, interner).or_abrupt()?.kind(),
+                            TokenKind::Punctuator(Punctuator::Arrow)
+                        )))
                 {
                     return Ok(
                         AsyncArrowFunction::new(self.name, self.allow_in, self.allow_yield)

core/parser/src/parser/expression/tests.rs

@@ -10,7 +10,8 @@ use boa_ast::{
         },
         Call, Identifier, Parenthesized, RegExpLiteral,
     },
-    Declaration, Expression, Statement,
+    function::{AsyncArrowFunction, FormalParameter, FormalParameterList},
+    Declaration, Expression, Script, Statement,
 };
 use boa_interner::{Interner, Sym};
 use boa_macros::utf16;
@@ -685,6 +686,29 @@ fn check_logical_expressions() {
     check_invalid_script("a || b ?? c");
 }
 
+#[test]
+fn parse_async_arrow_function_named_of() {
+    let interner = &mut Interner::default();
+    check_script_parser(
+        "async of => {}",
+        vec![
+            Statement::Expression(Expression::from(AsyncArrowFunction::new(
+                None,
+                FormalParameterList::from_parameters(vec![FormalParameter::new(
+                    Variable::from_identifier(
+                        Identifier::new(interner.get_or_intern_static("of", utf16!("of"))),
+                        None,
+                    ),
+                    false,
+                )]),
+                Script::default(),
+            )))
+            .into(),
+        ],
+        interner,
+    );
+}
+
 macro_rules! check_non_reserved_identifier {
     ($keyword:literal) => {{
         let interner = &mut Interner::default();

core/parser/src/parser/statement/iteration/for_statement.rs

@@ -111,6 +111,7 @@ where
             }
         };
 
+        let mut init_is_async_of = false;
         let init = match cursor.peek(0, interner).or_abrupt()?.kind().clone() {
             TokenKind::Keyword((Keyword::Var, _)) => {
                 cursor.advance(interner);
@@ -135,19 +136,18 @@ where
                     .into(),
             ),
             TokenKind::Keyword((Keyword::Async, false)) if !r#await => {
-                match cursor.peek(1, interner).or_abrupt()?.kind() {
-                    TokenKind::Keyword((Keyword::Of, _)) => {
-                        return Err(Error::lex(LexError::Syntax(
-                            "invalid left-hand side expression 'async' of a for-of loop".into(),
-                            init_position,
-                        )));
+                if matches!(
+                    cursor.peek(1, interner).or_abrupt()?.kind(),
+                    TokenKind::Keyword((Keyword::Of, false))
+                ) {
+                    init_is_async_of = true;
                 }
-                    _ => Some(
+
+                Some(
                     Expression::new(None, false, self.allow_yield, self.allow_await)
                         .parse(cursor, interner)?
                         .into(),
-                    ),
-                }
+                )
             }
             TokenKind::Punctuator(Punctuator::Semicolon) => None,
             _ => Some(
@@ -181,6 +181,17 @@ where
                 {
                     return Err(Error::general("unexpected token", position));
                 }
+                if init_is_async_of
+                    && init
+                        == ForLoopInitializer::Expression(ast::Expression::Identifier(
+                            Identifier::new(Sym::ASYNC),
+                        ))
+                {
+                    return Err(Error::lex(LexError::Syntax(
+                        "invalid left-hand side expression 'async' of a for-of loop".into(),
+                        init_position,
+                    )));
+                }
 
                 let in_loop = kw == &Keyword::In;
                 let init = initializer_to_iterable_loop_initializer(