fix(typescript): parse contextual keyword: 'interface I { [type: K]: V; }'

Author: strager

docs/CHANGELOG.md

@@ -13,6 +13,8 @@ Semantic Versioning.
 * TypeScript support (still experimental):
   * Assigning to a variable with the same name as an `import`ed type no longer
     falsely reports [E0185][] ("assignment to imported variable").
+  * Interface index signature variables can now be named contextual keywords
+    such as `type`.
 
 ## 2.19.0 (2023-12-30)
 

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

@@ -717,8 +717,9 @@ void Parser::parse_and_visit_class_or_interface_member(
     // [key: KeyType]: ValueType;  // TypeScript only
     bool try_parse_typescript_index_signature(const Char8 *left_square_begin) {
       Lexer_Transaction transaction = p->lexer_.begin_transaction();
-      // TODO(strager): Allow certain contextual keywords like 'let'?
-      if (p->peek().type == Token_Type::identifier) {
+      switch (p->peek().type) {
+      QLJS_CASE_CONTEXTUAL_KEYWORD:
+      case Token_Type::identifier: {
         Identifier key_variable = p->peek().identifier_name();
         p->skip();
         if (p->peek().type == Token_Type::colon) {
@@ -793,6 +794,11 @@ void Parser::parse_and_visit_class_or_interface_member(
           v.visit_exit_index_signature_scope();
           return true;
         }
+        break;
+      }
+
+      default:
+        break;
       }
       p->lexer_.roll_back_transaction(std::move(transaction));
       return false;

test/test-parse-typescript-interface.cpp

@@ -679,6 +679,19 @@ TEST_F(Test_Parse_TypeScript_Interface, interface_with_index_signature) {
   }
 }
 
+TEST_F(Test_Parse_TypeScript_Interface,
+       index_signature_variable_can_be_named_contextual_keyword) {
+  for (String8_View keyword : contextual_keywords) {
+    Spy_Visitor p =
+        test_parse_and_visit_statement(concat(u8"interface I { ["_sv, keyword,
+                                              u8": KeyType]: ValueType; }"_sv),
+                                       no_diags, typescript_options);
+    EXPECT_THAT(p.variable_declarations,
+                ElementsAreArray({interface_decl(u8"I"_sv),
+                                  index_signature_param_decl(keyword)}));
+  }
+}
+
 TEST_F(Test_Parse_TypeScript_Interface, index_signature_requires_type) {
   {
     Spy_Visitor p = test_parse_and_visit_statement(