fix(typescript): fix crash on optional parameter named 'readonly'

Author: strager

docs/CHANGELOG.md

@@ -125,6 +125,8 @@ Semantic Versioning.
     assertion failure.
   * Subnamespaces can now be named contextual keywords such as `string`.
   * Import aliases can now be named contextual keywords such as `implements`.
+  * Optional function parameters can now be named contextual keywords such as
+    `readonly`.
   * Import aliases can now be declared with `import type`.
   * Namespace aliases can now reference variables named contextual keywords such as
     `yield` inside namespaces.

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

@@ -2530,10 +2530,12 @@ void Parser::parse_and_visit_function_parameters(
       switch (this->peek().type) {
       // function foo(paramName = def) {}
       // function foo(paramName: any) {}   // TypeScript only.
+      // function foo(paramName?) {}       // TypeScript only.
       // function foo(paramName) {}
       case Token_Type::colon:
       case Token_Type::comma:
       case Token_Type::equal:
+      case Token_Type::question:
       case Token_Type::right_paren:
         return true;
 

test/test-parse-typescript-function.cpp

@@ -760,6 +760,16 @@ TEST_F(Test_Parse_TypeScript_Function, optional_parameter) {
                           }));
   }
 
+  for (String8_View parameter_name : contextual_keywords) {
+    Spy_Visitor p = test_parse_and_visit_statement(
+        concat(u8"function f("_sv, parameter_name, u8"?) {}"_sv), no_diags,
+        typescript_options);
+    EXPECT_THAT(p.variable_declarations, ElementsAreArray({
+                                             func_param_decl(parameter_name),
+                                             function_decl(u8"f"_sv),
+                                         }));
+  }
+
   {
     Spy_Visitor p = test_parse_and_visit_statement(
         u8"(param?) => {}"_sv, no_diags, typescript_options);