Declare the arguments object before creating the function var, to make sure it masks it

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index b1f7c667ef9ac4b5c115bdab0cbef30de7ae5e90..29b26055c3d8e7519e097c6fe912437c63712242 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -2842,10 +2842,6 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
 
     // Parsing the body may change the language mode in our scope.
     language_mode = scope->language_mode();
-    scope->DeclareArguments(ast_value_factory());
-    if (main_scope != scope) {
-      main_scope->DeclareArguments(ast_value_factory());
-    }
 
     // Validate name and parameter names. We can do this only after parsing the
     // function, since the function can declare itself strict.
@@ -3434,6 +3430,13 @@ ZoneList<Statement*>* Parser::ParseEagerFunctionBody(
     }
   }
 
+  if (!IsArrowFunction(kind)) {
+    // Declare arguments after parsing the function since lexical 'arguments'
+    // masks the arguments object. Declare arguments before declaring the
+    // function var since the arguments object masks 'function arguments'.
+    function_scope->DeclareArguments(ast_value_factory());
+  }
+
   if (function_type == FunctionLiteral::kNamedExpression) {
     Statement* statement;
     if (function_scope->LookupLocal(function_name) == nullptr) {