Rewind additional parser state when reinterpreting arrow arguments

src/preparser.h

 // 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.
 
 #ifndef V8_PREPARSER_H
 #define V8_PREPARSER_H
 
 #include "src/v8.h"
 
 #include "src/func-name-inferrer.h"
@@ skipping 96 matching lines @@
   void set_allow_arrow_functions(bool allow) { allow_arrow_functions_ = allow; }
   void set_allow_modules(bool allow) { scanner()->SetHarmonyModules(allow); }
   void set_allow_harmony_scoping(bool allow) {
     scanner()->SetHarmonyScoping(allow);
   }
   void set_allow_harmony_numeric_literals(bool allow) {
     scanner()->SetHarmonyNumericLiterals(allow);
   }
 
  protected:
+  friend class Traits::Type::Checkpoint;
+
   enum AllowEvalOrArgumentsAsIdentifier {
     kAllowEvalOrArguments,
     kDontAllowEvalOrArguments
   };
 
   enum Mode {
     PARSE_LAZILY,
     PARSE_EAGERLY
   };
 
+  class ParserCheckpoint;
+
   // ---------------------------------------------------------------------------
   // FunctionState and BlockState together implement the parser's scope stack.
   // The parser's current scope is in scope_. BlockState and FunctionState
   // constructors push on the scope stack and the destructors pop. They are also
   // used to hold the parser's per-function and per-block state.
   class BlockState BASE_EMBEDDED {
    public:
     BlockState(typename Traits::Type::Scope** scope_stack,
                typename Traits::Type::Scope* scope)
         : scope_stack_(scope_stack),
@@ skipping 75 matching lines @@
 
     FunctionState** function_state_stack_;
     FunctionState* outer_function_state_;
     typename Traits::Type::Scope** scope_stack_;
     typename Traits::Type::Scope* outer_scope_;
     int saved_ast_node_id_;  // Only used by ParserTraits.
     typename Traits::Type::Zone* extra_param_;
     typename Traits::Type::Factory factory_;
 
     friend class ParserTraits;
+    friend class ParserCheckpoint;
+  };
+
+  // Annoyingly, arrow functions first parse as comma expressions, then when we
+  // see the => we have to go back and reinterpret the arguments as being formal
+  // parameters.  To do so we need to reset some of the parser state back to
+  // what it was before the arguments were first seen.
+  class ParserCheckpoint : public Traits::Type::Checkpoint {
+   public:
+    ParserCheckpoint() : Traits::Type::Checkpoint() {}
+
+    void Save(ParserBase* parser) {
+      Traits::Type::Checkpoint::Save(parser);
+      function_state_ = parser->function_state_;
+      next_materialized_literal_index_ =
+          function_state_->next_materialized_literal_index_;
+      next_handler_index_ = function_state_->next_handler_index_;
+      expected_property_count_ = function_state_->expected_property_count_;
+    }
+
+    void Restore() {
+      Traits::Type::Checkpoint::Restore();
+      function_state_->next_materialized_literal_index_ =
+          next_materialized_literal_index_;
+      function_state_->next_handler_index_ = next_handler_index_;
+      function_state_->expected_property_count_ = expected_property_count_;
+    }
+
+   private:
+    FunctionState* function_state_;
+    int next_materialized_literal_index_;
+    int next_handler_index_;
+    int expected_property_count_;
   };
 
   class ParsingModeScope BASE_EMBEDDED {
    public:
     ParsingModeScope(ParserBase* parser, Mode mode)
         : parser_(parser),
           old_mode_(parser->mode()) {
       parser_->mode_ = mode;
     }
     ~ParsingModeScope() {
@@ skipping 782 matching lines @@
   // dummy method right in this class.
   PreParserFactory* visitor() { return this; }
   BailoutReason dont_optimize_reason() { return kNoReason; }
   int* ast_properties() {
     static int dummy = 42;
     return &dummy;
   }
 };
 
 
+class PreParserCheckpoint BASE_EMBEDDED {
+ public:
+  PreParserCheckpoint() {}
+  template <typename Parser>
+  void Save(Parser* parser) {}
+  void Restore() {}
+};
+
+
 class PreParser;
 
 class PreParserTraits {
  public:
   struct Type {
     // TODO(marja): To be removed. The Traits object should contain all the data
     // it needs.
     typedef PreParser* Parser;
 
     // Used by FunctionState and BlockState.
     typedef PreParserScope Scope;
     typedef PreParserScope ScopePtr;
+    typedef PreParserCheckpoint Checkpoint;
 
     // PreParser doesn't need to store generator variables.
     typedef void GeneratorVariable;
     // No interaction with Zones.
     typedef void Zone;
 
     typedef int AstProperties;
     typedef Vector<PreParserIdentifier> ParameterIdentifierVector;
 
     // Return types for traversing functions.
@@ skipping 948 matching lines @@
   //   YieldExpression
   //   LeftHandSideExpression AssignmentOperator AssignmentExpression
 
   Scanner::Location lhs_location = scanner()->peek_location();
 
   if (peek() == Token::YIELD && is_generator()) {
     return this->ParseYieldExpression(ok);
   }
 
   if (fni_ != NULL) fni_->Enter();
+  ParserCheckpoint checkpoint;
+  checkpoint.Save(this);

[rossberg, 2014/08/05 13:51:31]

Why the separate Save method instead of just

  ParserCheckpoint checkpoint(this);

   ExpressionT expression =
       this->ParseConditionalExpression(accept_IN, CHECK_OK);
 
   if (allow_arrow_functions() && peek() == Token::ARROW) {
+    checkpoint.Restore();
     expression = this->ParseArrowFunctionLiteral(lhs_location.beg_pos,
                                                  expression, CHECK_OK);
     return expression;
   }
 
   if (!Token::IsAssignmentOp(peek())) {
     if (fni_ != NULL) fni_->Leave();
     // Parsed conditional expression only (no assignment).
     return expression;
   }
@@ skipping 586 matching lines @@
       parser()->ReportMessage("accessor_get_set");
     }
     *ok = false;
   }
 }
 
 
 } }  // v8::internal
 
 #endif  // V8_PREPARSER_H