[parser] Rewritable expressions should not be valid variable references

src/ast/ast.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/ast.h"
 
 #include <cmath>  // For isfinite.
 
 #include "src/ast/prettyprinter.h"
 #include "src/ast/scopes.h"
@@ skipping 107 matching lines @@
 
 bool Expression::ToBooleanIsTrue() const {
   return IsLiteral() && AsLiteral()->ToBooleanIsTrue();
 }
 
 bool Expression::ToBooleanIsFalse() const {
   return IsLiteral() && AsLiteral()->ToBooleanIsFalse();
 }
 
 bool Expression::IsValidReferenceExpression() const {
+  // We don't want expressions wrapped inside RewritableExpression to be
+  // considered as valid reference expressions, as they will be rewritten
+  // to something (most probably involving a do expression).
+  if (IsRewritableExpression()) return false;

[Michael Starzinger, 2016/07/18 13:08:04]

I am confused, how can the below predicate return true for a
RewritableExpression?

[Michael Starzinger, 2016/07/18 13:10:13]

Ah, now I see, the IsFoo predicates actually special case for
RewritableExpression ... oh god ...

[nickie, 2016/07/18 13:13:18]

That's the point.  They never should be.  They never were before CL 2126233002. 
The default for Expression was false:

https://codereview.chromium.org/2126233002/diff/180001/src/ast/ast.h#oldcode300

and that CL changed it:

https://codereview.chromium.org/2126233002/diff/180001/src/ast/ast.cc#newcode136

   return IsProperty() ||
          (IsVariableProxy() && AsVariableProxy()->IsValidReferenceExpression());
 }
 
 bool Expression::IsValidReferenceExpressionOrThis() const {
   return IsValidReferenceExpression() ||
          (IsVariableProxy() && AsVariableProxy()->is_this());
 }
 
 bool Expression::IsAnonymousFunctionDefinition() const {
@@ skipping 1096 matching lines @@
 bool Literal::Match(void* literal1, void* literal2) {
   const AstValue* x = static_cast<Literal*>(literal1)->raw_value();
   const AstValue* y = static_cast<Literal*>(literal2)->raw_value();
   return (x->IsString() && y->IsString() && x->AsString() == y->AsString()) ||
          (x->IsNumber() && y->IsNumber() && x->AsNumber() == y->AsNumber());
 }
 
 
 }  // namespace internal
 }  // namespace v8