[es7] implement |do| expressions proposal

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index af6ecb8d10647d27faf9d01f5dc37928b30b77aa..66979eb0657a5fd2a4e2c89f76886bf4e984853a 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -90,7 +90,8 @@ namespace internal {
   V(SuperPropertyReference)     \
   V(SuperCallReference)         \
   V(CaseClause)                 \
-  V(EmptyParentheses)
+  V(EmptyParentheses)           \
+  V(DoExpression)
 
 #define AST_NODE_LIST(V)                        \
   DECLARATION_NODE_LIST(V)                      \
@@ -490,6 +491,29 @@ class Block final : public BreakableStatement {
 };
 
 
+class DoExpression final : public Expression {
+ public:
+  DECLARE_NODE_TYPE(DoExpression)
+
+  Block* block() { return block_; }
+  VariableProxy* result() { return result_; }
+
+ protected:
+  DoExpression(Zone* zone, Block* block, VariableProxy* result, int pos)
+      : Expression(zone, pos), block_(block), result_(result) {
+    DCHECK_NOT_NULL(block_);
+    DCHECK_NOT_NULL(result_);
+  }
+  static int parent_num_ids() { return Expression::num_ids(); }
+
+ private:
+  int local_id(int n) const { return base_id() + parent_num_ids() + n; }
+
+  Block* block_;
+  VariableProxy* result_;
+};
+
+
 class Declaration : public AstNode {
  public:
   VariableProxy* proxy() const { return proxy_; }
@@ -3558,6 +3582,11 @@ class AstNodeFactory final BASE_EMBEDDED {
         NativeFunctionLiteral(parser_zone_, name, extension, pos);
   }
 
+  DoExpression* NewDoExpression(Block* block, Variable* result_var, int pos) {
+    VariableProxy* result = NewVariableProxy(result_var, pos);
+    return new (parser_zone_) DoExpression(parser_zone_, block, result, pos);
+  }
+
   ThisFunction* NewThisFunction(int pos) {
     return new (local_zone_) ThisFunction(local_zone_, pos);
   }