fix(typescript): don't double-parse for 'await <T>() => {x}'

visit_variable_use("x") occurs twice when parsing
'await <T>() => {x}'. This is bad. Fix it.

docs/CHANGELOG.md

@@ -168,6 +168,7 @@ Semantic Versioning.
     to make an optional type").
   * `class T<T> {}` no longer falsely reports [E0034][] ("redeclaration of
     variable").
+  * `await <T>() => {}` no longer does confusing things.
 
 ## 2.18.0 (2023-11-03)
 

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

@@ -1287,16 +1287,15 @@ Expression* Parser::parse_await_expression(Parse_Visitor_Base& v,
         Parser_Transaction transaction = this->begin_transaction();
 
         bool parsed_ok = this->catch_fatal_parse_errors([&] {
-          // FIXME(#831): v should not be used here. We should use a
-          // buffering_visitor.
           if (this->in_top_level_) {
             // Try to parse the / as a regular expression literal or the < as a
             // JSX element.
-            [[maybe_unused]] Expression* ast = this->parse_expression(v, prec);
+            [[maybe_unused]] Expression* ast =
+                this->parse_expression(Null_Visitor::instance, prec);
           } else {
             // Try to parse the / or < as a binary operator.
             [[maybe_unused]] Expression* ast = this->parse_expression_remainder(
-                v,
+                Null_Visitor::instance,
                 this->make_expression<Expression::Variable>(
                     await_token.identifier_name(), await_token.type),
                 prec);

test/test-parse-typescript-generic-arrow.cpp

@@ -391,6 +391,17 @@ TEST_F(Test_Parse_TypeScript_Generic_Arrow,
     }
   }
 }
+
+TEST_F(Test_Parse_TypeScript_Generic_Arrow,
+       generic_async_function_with_await_keyword) {
+  {
+    Spy_Visitor p = test_parse_and_visit_expression(
+        u8"await <T>() => { await(myPromise); }"_sv,
+        u8"^^^^^ Diag_Await_Followed_By_Arrow_Function.await_operator"_diag,
+        typescript_options);
+    EXPECT_THAT(p.variable_uses, ElementsAreArray({u8"myPromise"_sv}));
+  }
+}
 }
 }