[es6] Correct length for functions with default parameters

src/scopes.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_SCOPES_H_
 #define V8_SCOPES_H_
 
 #include "src/ast.h"
 #include "src/pending-compilation-error-handler.h"
 #include "src/zone.h"
@@ skipping 110 matching lines @@
     DCHECK(is_function_scope());
     // Handle implicit declaration of the function name in named function
     // expressions before other declarations.
     decls_.InsertAt(0, declaration, zone());
     function_ = declaration;
   }
 
   // Declare a parameter in this scope.  When there are duplicated
   // parameters the rightmost one 'wins'.  However, the implementation
   // expects all parameters to be declared and from left to right.
-  Variable* DeclareParameter(const AstRawString* name, VariableMode mode,
-                             bool is_rest, bool* is_duplicate);
+  Variable* DeclareParameter(
+      const AstRawString* name, VariableMode mode,
+      bool is_optional, bool is_rest, bool* is_duplicate);
 
   // Declare a local variable in this scope. If the variable has been
   // declared before, the previously declared variable is returned.
   Variable* DeclareLocal(const AstRawString* name, VariableMode mode,
                          InitializationFlag init_flag, Variable::Kind kind,
                          MaybeAssignedFlag maybe_assigned_flag = kNotAssigned,
                          int declaration_group_start = -1);
 
   // Declare an implicit global variable in this scope which must be a
   // script scope.  The variable was introduced (possibly from an inner
@@ skipping 215 matching lines @@
     return function_;
   }
 
   // Parameters. The left-most parameter has index 0.
   // Only valid for function scopes.
   Variable* parameter(int index) const {
     DCHECK(is_function_scope());
     return params_[index];
   }
 
-  // Returns the default function arity --- does not include rest parameters.
-  int default_function_length() const {
-    int count = params_.length();
-    if (rest_index_ >= 0) {
-      DCHECK(count > 0);
-      DCHECK(is_function_scope());
-      --count;
-    }
-    return count;
-  }
+  // Returns the default function arity excluding default or rest parameters.
+  int default_function_length() const { return arity_; }
 
   int num_parameters() const { return params_.length(); }
 
   // A function can have at most one rest parameter. Returns Variable* or NULL.
   Variable* rest_parameter(int* index) const {
     *index = rest_index_;
     if (rest_index_ < 0) return NULL;
     return rest_parameter_;
   }
 
@@ skipping 237 matching lines @@
   int num_heap_slots_;
   int num_global_slots_;
 
   // The number of modules (including nested ones).
   int num_modules_;
 
   // For module scopes, the host scope's temporary variable binding this module.
   Variable* module_var_;
 
   // Info about the parameter list of a function.
+  int arity_;
   bool has_simple_parameters_;
   Variable* rest_parameter_;
   int rest_index_;
 
   // Serialized scope info support.
   Handle<ScopeInfo> scope_info_;
   bool already_resolved() { return already_resolved_; }
 
   // Create a non-local variable with a given name.
   // These variables are looked up dynamically at runtime.
@@ skipping 120 matching lines @@
   PendingCompilationErrorHandler pending_error_handler_;
 
   // For tracking which classes are declared consecutively. Needed for strong
   // mode.
   int class_declaration_group_start_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_SCOPES_H_