Allow lexically declared "arguments" in function scope in sloppy mode.

src/ast/scopes.cc

Index: src/ast/scopes.cc
diff --git a/src/ast/scopes.cc b/src/ast/scopes.cc
index 73c243b6250c21e4adccb99288be13b8b803707e..571da099e1bd2f6aa0a876154f9c8bb00e817c77 100644
--- a/src/ast/scopes.cc
+++ b/src/ast/scopes.cc
@@ -436,15 +436,26 @@ void DeclarationScope::DeclareThis(AstValueFactory* ast_value_factory) {
   receiver_ = var;
 }
 
-void DeclarationScope::DeclareDefaultFunctionVariables(
-    AstValueFactory* ast_value_factory) {
+void DeclarationScope::DeclareArguments(AstValueFactory* ast_value_factory) {
   DCHECK(is_function_scope());
   DCHECK(!is_arrow_scope());
+
+  Variable* arg_variable = LookupLocal(ast_value_factory->arguments_string());
+  if (arg_variable != NULL && IsLexicalVariableMode(arg_variable->mode())) {

[adamk, 2016/08/30 20:45:56]

Please add a comment here explaining what you're doing. You could refer to the
spec, since the spec in
https://tc39.github.io/ecma262/#sec-functiondeclarationinstantiation does this
exact check.

Also style nit: please use nullptr instead of NULL in new code.

[lpy, 2016/09/01 01:17:30]

Done.

+    return;
+  }
+
   // Declare 'arguments' variable which exists in all non arrow functions.
   // Note that it might never be accessed, in which case it won't be
   // allocated during variable allocation.
   arguments_ = Declare(zone(), this, ast_value_factory->arguments_string(), VAR,

[adamk, 2016/08/30 20:45:56]

I think you only need to do this if arg_variable == nullptr (otherwise
arg_variable is the same Variable* that Declare will return).

[lpy, 2016/09/01 01:17:30]

Done.

                        Variable::ARGUMENTS, kCreatedInitialized);
+}
+
+void DeclarationScope::DeclareDefaultFunctionVariables(
+    AstValueFactory* ast_value_factory) {
+  DCHECK(is_function_scope());
+  DCHECK(!is_arrow_scope());
 
   new_target_ = Declare(zone(), this, ast_value_factory->new_target_string(),
                         CONST, Variable::NORMAL, kCreatedInitialized);
@@ -1501,9 +1512,6 @@ void DeclarationScope::AllocateParameterLocals() {
       // allocate the arguments object by nulling out arguments_.
       arguments_ = nullptr;
     }
-
-  } else {
-    DCHECK(is_arrow_scope());
   }
 
   // The same parameter may occur multiple times in the parameters_ list.