Temporal dead zone behaviour for let bindings.

src/hydrogen.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3103 matching lines @@
 }
 
 
 void HGraphBuilder::VisitVariableProxy(VariableProxy* expr) {
   ASSERT(!HasStackOverflow());
   ASSERT(current_block() != NULL);
   ASSERT(current_block()->HasPredecessor());
   Variable* variable = expr->AsVariable();
   if (variable == NULL) {
     return Bailout("reference to rewritten variable");
+  } else if (variable->mode() == Variable::LET) {
+    return Bailout("reference to let variable");
   } else if (variable->IsStackAllocated()) {
     HValue* value = environment()->Lookup(variable);
     if (variable->mode() == Variable::CONST &&
         value == graph()->GetConstantHole()) {
       return Bailout("reference to uninitialized const variable");
     }
     return ast_context()->ReturnValue(value);
   } else if (variable->IsContextSlot()) {
     if (variable->mode() == Variable::CONST) {
       return Bailout("reference to const context slot");
@@ skipping 445 matching lines @@
   VariableProxy* proxy = target->AsVariableProxy();
   Variable* var = proxy->AsVariable();
   Property* prop = target->AsProperty();
   ASSERT(var == NULL || prop == NULL);
 
   // We have a second position recorded in the FullCodeGenerator to have
   // type feedback for the binary operation.
   BinaryOperation* operation = expr->binary_operation();
 
   if (var != NULL) {
-    if (var->mode() == Variable::CONST)  {
-      return Bailout("unsupported const compound assignment");
+    if (var->mode() == Variable::CONST ||
+        var->mode() == Variable::LET)  {
+      return Bailout("unsupported let or const compound assignment");
     }
 
     CHECK_ALIVE(VisitForValue(operation));
 
     if (var->is_global()) {
       HandleGlobalVariableAssignment(var,
                                      Top(),
                                      expr->position(),
                                      expr->AssignmentId());
     } else if (var->IsStackAllocated()) {
@@ skipping 122 matching lines @@
       if (expr->op() != Token::INIT_CONST) {
         return Bailout("non-initializer assignment to const");
       }
       if (!var->IsStackAllocated()) {
         return Bailout("assignment to const context slot");
       }
       // We insert a use of the old value to detect unsupported uses of const
       // variables (e.g. initialization inside a loop).
       HValue* old_value = environment()->Lookup(var);
       AddInstruction(new HUseConst(old_value));
+    } else if (var->mode() == Variable::LET) {
+      return Bailout("unsupported assignment to let");
     }
 
     if (proxy->IsArguments()) return Bailout("assignment to arguments");
 
     // Handle the assignment.
     if (var->IsStackAllocated()) {
       // We do not allow the arguments object to occur in a context where it
       // may escape, but assignments to stack-allocated locals are
       // permitted.
       CHECK_ALIVE(VisitForValue(expr->value(), ARGUMENTS_ALLOWED));
@@ skipping 2058 matching lines @@
   ASSERT(current_block() != NULL);
   ASSERT(current_block()->HasPredecessor());
   HThisFunction* self = new(zone()) HThisFunction;
   return ast_context()->ReturnInstruction(self, expr->id());
 }
 
 
 void HGraphBuilder::VisitDeclaration(Declaration* decl) {
   // We support only declarations that do not require code generation.
   Variable* var = decl->proxy()->var();
-  if (!var->IsStackAllocated() || decl->fun() != NULL) {
+  if (!var->IsStackAllocated() ||
+      decl->fun() != NULL ||
+      decl->mode() == Variable::LET) {
     return Bailout("unsupported declaration");
   }
 
   if (decl->mode() == Variable::CONST) {
     ASSERT(var->IsStackAllocated());
     environment()->Bind(var, graph()->GetConstantHole());
   }
 }
 
 
@@ skipping 927 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify();
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal