[esnext] implement frontend changes for async/await proposal

src/ast/ast.h

Index: src/ast/ast.h
diff --git a/src/ast/ast.h b/src/ast/ast.h
index 8a503301484ee0f91e6901cbaf6d469306faa94f..ec4b70192844c4a5d6d07ae0814e56f2744251f3 100644
--- a/src/ast/ast.h
+++ b/src/ast/ast.h
@@ -392,6 +392,9 @@ class Expression : public AstNode {
   int base_id_;
   Bounds bounds_;
   class ToBooleanTypesField : public BitField16<uint16_t, 0, 9> {};
+
+ protected:
+  static const int kExpressionBitFieldNext = ToBooleanTypesField::kNext;
   uint16_t bit_field_;
   // Ends with 16-bit field; deriving classes in turn begin with
   // 16-bit fields for optimum packing efficiency.
@@ -2589,7 +2592,9 @@ class FunctionLiteral final : public Expression {
   int start_position() const;
   int end_position() const;
   int SourceSize() const { return end_position() - start_position(); }
-  bool is_declaration() const { return IsDeclaration::decode(bitfield_); }
+  bool is_declaration() const {
+    return IsDeclaration::decode(Expression::bit_field_);
+  }
   bool is_named_expression() const {
     return IsNamedExpression::decode(bitfield_);
   }
@@ -2716,7 +2721,6 @@ class FunctionLiteral final : public Expression {
         function_token_position_(RelocInfo::kNoPosition),
         yield_count_(0) {
     bitfield_ =
-        IsDeclaration::encode(function_type == kDeclaration) |
         IsNamedExpression::encode(function_type == kNamedExpression) |
         IsAnonymousExpression::encode(function_type == kAnonymousExpression) |
         Pretenure::encode(false) |
@@ -2729,15 +2733,17 @@ class FunctionLiteral final : public Expression {
   }
 
  private:
-  class IsDeclaration : public BitField16<bool, 0, 1> {};
-  class IsNamedExpression : public BitField16<bool, 1, 1> {};
-  class IsAnonymousExpression : public BitField16<bool, 2, 1> {};
-  class Pretenure : public BitField16<bool, 3, 1> {};
-  class HasDuplicateParameters : public BitField16<bool, 4, 1> {};
-  class IsFunction : public BitField16<bool, 5, 1> {};
-  class ShouldEagerCompile : public BitField16<bool, 6, 1> {};
-  class ShouldBeUsedOnceHint : public BitField16<bool, 7, 1> {};
-  class FunctionKindBits : public BitField16<FunctionKind, 8, 8> {};
+  STATIC_ASSERT((Expression::kExpressionBitFieldNext + 1) < 16);
+  class IsDeclaration
+      : public BitField16<bool, Expression::kExpressionBitFieldNext, 1> {};
+  class IsNamedExpression : public BitField16<bool, 0, 1> {};
+  class IsAnonymousExpression : public BitField16<bool, 1, 1> {};
+  class Pretenure : public BitField16<bool, 2, 1> {};
+  class HasDuplicateParameters : public BitField16<bool, 3, 1> {};
+  class IsFunction : public BitField16<bool, 4, 1> {};
+  class ShouldEagerCompile : public BitField16<bool, 5, 1> {};
+  class ShouldBeUsedOnceHint : public BitField16<bool, 6, 1> {};
+  class FunctionKindBits : public BitField16<FunctionKind, 7, 9> {};
 
   // Start with 16-bit field, which should get packed together
   // with Expression's trailing 16-bit field.