Declare 'this' as DYNAMIC_GLOBAL on the script_scope

src/ast/scopes.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/ast/scopes.h"
 
 #include <set>
 
 #include "src/accessors.h"
 #include "src/bootstrapper.h"
@@ skipping 1234 matching lines @@
   }
 }
 
 void Scope::CheckZones() {
   for (Scope* scope = inner_scope_; scope != nullptr; scope = scope->sibling_) {
     CHECK_EQ(scope->zone(), zone());
   }
 }
 #endif  // DEBUG
 
-Variable* Scope::NonLocal(const AstRawString* name, VariableMode mode,
-                          Variable::Kind kind) {
+Variable* Scope::NonLocal(const AstRawString* name, VariableMode mode) {
   if (dynamics_ == NULL) dynamics_ = new (zone()) DynamicScopePart(zone());
   VariableMap* map = dynamics_->GetMap(mode);
   Variable* var = map->Lookup(name);
   if (var == NULL) {
     // Declare a new non-local.
     InitializationFlag init_flag = (mode == VAR)
         ? kCreatedInitialized : kNeedsInitialization;
-    var = map->Declare(zone(), NULL, name, mode, kind, init_flag);
+    var = map->Declare(zone(), NULL, name, mode, Variable::NORMAL, init_flag);
     // Allocate it by giving it a dynamic lookup.
     var->AllocateTo(VariableLocation::LOOKUP, -1);
   }
   return var;
 }
 
 Variable* Scope::LookupRecursive(VariableProxy* proxy,
                                  BindingKind* binding_kind,
                                  AstNodeFactory* factory,
                                  Scope* max_outer_scope) {
   DCHECK(binding_kind != NULL);
   if (already_resolved() && is_with_scope()) {
     // Short-cut: if the scope is deserialized from a scope info, variable
     // allocation is already fixed.  We can simply return with dynamic lookup.
     *binding_kind = DYNAMIC_LOOKUP;
     return NULL;

[Toon Verwaest, 2016/08/11 16:06:15]

Doh. This "optimization" breaks the obvious case (for which we, surprisingly!,
don't have a test):

with ({}) a = ()=>{ "use strict"; delete this }; a()

It seems like this optimization will actually just slow down 99.999% of scope
resolutions by requiring the check. What about just dropping it?

   }
 
   // Try to find the variable in this scope.
   Variable* var = LookupLocal(proxy->raw_name());
 
   // We found a variable and we are done. (Even if there is an 'eval' in
   // this scope which introduces the same variable again, the resulting
   // variable remains the same.)
   if (var != NULL) {
     *binding_kind = BOUND;
@@ skipping 87 matching lines @@
                name->ToCString().get());
     }
     VariableLocation location = var->location();
     CHECK(location == VariableLocation::LOCAL ||
           location == VariableLocation::CONTEXT ||
           location == VariableLocation::PARAMETER ||
           location == VariableLocation::UNALLOCATED);
   }
 #endif
 
-  // TODO(verwaest): 'this' should always be declared and found. That way we can
-  // remove this workaround.
-  Variable::Kind kind = proxy->is_this() ? Variable::THIS : Variable::NORMAL;
   switch (binding_kind) {
     case BOUND:
       break;
 
     case BOUND_EVAL_SHADOWED:
       // We either found a variable binding that might be shadowed by eval  or
       // gave up on it (e.g. by encountering a local with the same in the outer
       // scope which was not promoted to a context, this can happen if we use
       // debugger to evaluate arbitrary expressions at a break point).
       if (var->IsGlobalObjectProperty()) {
-        var = NonLocal(proxy->raw_name(), DYNAMIC_GLOBAL, kind);
+        var = NonLocal(proxy->raw_name(), DYNAMIC_GLOBAL);
       } else if (var->is_dynamic()) {
-        var = NonLocal(proxy->raw_name(), DYNAMIC, kind);
+        var = NonLocal(proxy->raw_name(), DYNAMIC);
       } else {
         Variable* invalidated = var;
-        var = NonLocal(proxy->raw_name(), DYNAMIC_LOCAL, kind);
+        var = NonLocal(proxy->raw_name(), DYNAMIC_LOCAL);
         var->set_local_if_not_shadowed(invalidated);
       }
       break;
 
     case UNBOUND:
       // No binding has been found. Declare a variable on the global object.
-      var = info->script_scope()->DeclareDynamicGlobal(proxy->raw_name(), kind);
+      var = info->script_scope()->DeclareDynamicGlobal(proxy->raw_name(),
+                                                       Variable::NORMAL);
       break;
 
     case UNBOUND_EVAL_SHADOWED:
       // No binding has been found. But some scope makes a sloppy 'eval' call.
-      var = NonLocal(proxy->raw_name(), DYNAMIC_GLOBAL, kind);
+      var = NonLocal(proxy->raw_name(), DYNAMIC_GLOBAL);
       break;
 
     case DYNAMIC_LOOKUP:
       // The variable could not be resolved statically.
-      var = NonLocal(proxy->raw_name(), DYNAMIC, kind);
+      var = NonLocal(proxy->raw_name(), DYNAMIC);
       break;
   }
 
   DCHECK(var != NULL);
   if (proxy->is_assigned()) var->set_maybe_assigned();
 
   proxy->BindTo(var);
 }
 
 void Scope::ResolveVariablesRecursively(ParseInfo* info,
@@ skipping 361 matching lines @@
       function != NULL && function->proxy()->var()->IsContextSlot();
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS - num_global_slots() -
          (is_function_var_in_context ? 1 : 0);
 }
 
 
 int Scope::ContextGlobalCount() const { return num_global_slots(); }
 
 }  // namespace internal
 }  // namespace v8