From 7f97e337787e4773ad4da2ae6d321afb7a277fda Mon Sep 17 00:00:00 2001
From: Matthew Olsson <matthewcolsson@gmail.com>
Date: Thu, 17 Jun 2021 10:14:45 -0700
Subject: [PATCH] LibJS: Disallow 'yield' identifier initializer in
 GeneratorFunctions

---
 Userland/Libraries/LibJS/Parser.cpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/Userland/Libraries/LibJS/Parser.cpp b/Userland/Libraries/LibJS/Parser.cpp
index 482aea2c33..80ec1be7ac 100644
--- a/Userland/Libraries/LibJS/Parser.cpp
+++ b/Userland/Libraries/LibJS/Parser.cpp
@@ -1409,8 +1409,10 @@ NonnullRefPtr<FunctionNodeType> Parser::parse_function_node(u8 parse_options)
         consume(TokenType::Function);
         if (!is_generator) {
             is_generator = match(TokenType::Asterisk);
-            if (is_generator)
+            if (is_generator) {
                 consume(TokenType::Asterisk);
+                parse_options = parse_options | FunctionNodeParseOptions::IsGeneratorFunction;
+            }
         }
 
         if (FunctionNodeType::must_have_name() || match(TokenType::Identifier))
@@ -1499,6 +1501,10 @@ Vector<FunctionNode::Parameter> Parser::parse_formal_parameters(int& function_le
             has_default_parameter = true;
             function_length = parameters.size();
             default_value = parse_expression(2);
+
+            bool is_generator = parse_options & FunctionNodeParseOptions::IsGeneratorFunction;
+            if (is_generator && default_value && default_value->fast_is<Identifier>() && static_cast<Identifier&>(*default_value).string() == "yield"sv)
+                syntax_error("Generator function parameter initializer cannot contain a reference to an identifier named \"yield\"");
         }
         parameters.append({ move(parameter), default_value, is_rest });
         if (match(TokenType::ParenClose))