fix(fe): don't error on 'for await (async of [])'

docs/CHANGELOG.md

@@ -63,6 +63,9 @@ Semantic Versioning.
 * A newline between an arrow function and a parenthesized expression (e.g.
   `let f = () => {} /*newline*/ (console.log('x'));` no longer falsely reports
   [E0211][] ("missing parentheses around self-invoked function").
+* `for await (async of []);` no longer falsely reports [E0082][] ("assigning to
+  'async' in a for-of loop requires parentheses"). (`for (async of []);` still
+  reports the diagnostic.)
 * TypeScript support (still experimental):
   * Types named `await`, `implements`, `interface`, `let`, `package`, `private`,
     `protected`, `public`, `static`, and `yield` are now recognized in type

src/quick-lint-js/fe/parse-statement.cpp

@@ -3964,7 +3964,8 @@ void Parser::parse_and_visit_for(Parse_Visitor_Base &v) {
   Source_Code_Span for_token_span = this->peek().span();
   this->skip();
 
-  if (this->peek().type == Token_Type::kw_await) {
+  bool is_for_await = this->peek().type == Token_Type::kw_await;
+  if (is_for_await) {
     this->skip();
   }
 
@@ -4244,23 +4245,26 @@ void Parser::parse_and_visit_for(Parse_Visitor_Base &v) {
     Token async_token = this->peek();
 
     Lexer_Transaction transaction = this->lexer_.begin_transaction();
-    bool is_invalid_async_of_sequence = false;
+    bool is_async_of = false;
     this->skip();
     if (this->peek().type == Token_Type::kw_of) {
       this->skip();
       if (this->peek().type != Token_Type::equal_greater) {
-        is_invalid_async_of_sequence = true;
+        is_async_of = true;
       }
     }
     this->lexer_.roll_back_transaction(std::move(transaction));
 
     Expression *init_expression(nullptr);
-    if (is_invalid_async_of_sequence) {
+    if (is_async_of) {
+      // for await (async of things) {}
       // for (async of things) {}  // Invalid.
-      this->diag_reporter_->report(
-          Diag_Cannot_Assign_To_Variable_Named_Async_In_For_Of_Loop{
-              .async_identifier = async_token.span(),
-          });
+      if (!is_for_await) {
+        this->diag_reporter_->report(
+            Diag_Cannot_Assign_To_Variable_Named_Async_In_For_Of_Loop{
+                .async_identifier = async_token.span(),
+            });
+      }
 
       this->skip();
       QLJS_ASSERT(this->peek().type == Token_Type::kw_of);

test/test-parse-loop.cpp

@@ -1405,6 +1405,15 @@ TEST_F(Test_Parse_Loop,
   EXPECT_THAT(p.variable_uses, ElementsAreArray({u8"xs"}));
 }
 
+TEST_F(Test_Parse_Loop,
+       can_assign_to_variable_named_async_without_parentheses_in_for_await_of) {
+  Spy_Visitor p = test_parse_and_visit_statement(
+      u8"async function f() { for await (async of xs); }"_sv,  //
+      no_diags, javascript_options);
+  EXPECT_THAT(p.variable_assignments, ElementsAreArray({u8"async"}));
+  EXPECT_THAT(p.variable_uses, ElementsAreArray({u8"xs"}));
+}
+
 TEST_F(Test_Parse_Loop, for_loop_in_for_loop_header_crash) {
   // There used to be a use-after-free bug caused by a buffering_visitor copying
   // memory into another buffering_visitor, then the parser's