[modules] Assign cell indices at validation time.

src/ast/variables.h

 // Copyright 2011 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.
 
 #ifndef V8_AST_VARIABLES_H_
 #define V8_AST_VARIABLES_H_
 
 #include "src/ast/ast-value-factory.h"
 #include "src/globals.h"
 #include "src/zone/zone.h"
@@ skipping 82 matching lines @@
   VariableLocation location() const {
     return LocationField::decode(bit_field_);
   }
   VariableKind kind() const { return VariableKindField::decode(bit_field_); }
   InitializationFlag initialization_flag() const {
     return InitializationFlagField::decode(bit_field_);
   }
 
   int index() const { return index_; }
 
-  // Sentinel index values for module exports and imports.
-  enum { kModuleExportIndex, kModuleImportIndex };
-
   bool IsExport() const {
-    DCHECK(location() == VariableLocation::MODULE);
-    return index() == kModuleExportIndex;
+    DCHECK_EQ(location(), VariableLocation::MODULE);
+    DCHECK_NE(index(), 0);

[adamk, 2016/10/31 18:25:04]

So this 0 appears in lots of places, but as I think more about it I'm not sure
it'd be any more clear to make it a constant. I do think this needs to be
clearly documented somewhere. Thoughts on where that might be?

[neis, 2016/11/03 10:43:48]

There's a comment now in modules.h.

+    return index() > 0;
   }
 
   void AllocateTo(VariableLocation location, int index) {
     DCHECK(IsUnallocated() ||
            (this->location() == location && this->index() == index));
-    DCHECK_IMPLIES(location == VariableLocation::MODULE,
-                   index == kModuleExportIndex || index == kModuleImportIndex);
+    DCHECK_IMPLIES(location == VariableLocation::MODULE, index != 0);
     bit_field_ = LocationField::update(bit_field_, location);
     DCHECK_EQ(location, this->location());
     index_ = index;
   }
 
   static InitializationFlag DefaultInitializationFlag(VariableMode mode) {
     DCHECK(IsDeclaredVariableMode(mode));
     return mode == VAR ? kCreatedInitialized : kNeedsInitialization;
   }
 
@@ skipping 22 matching lines @@
   class InitializationFlagField
       : public BitField16<InitializationFlag, IsUsedField::kNext, 2> {};
   class MaybeAssignedFlagField
       : public BitField16<MaybeAssignedFlag, InitializationFlagField::kNext,
                           2> {};
 };
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_VARIABLES_H_