[runtime] Optimize and unify rest parameters.

src/ast/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_AST_SCOPES_H_
 #define V8_AST_SCOPES_H_
 
 #include "src/ast/ast.h"
 #include "src/hashmap.h"
 #include "src/pending-compilation-error-handler.h"
@@ skipping 410 matching lines @@
   // 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 excluding default or rest parameters.
   int default_function_length() const { return arity_; }
 
-  int num_parameters() const { return params_.length(); }
+  // Returns the number of formal parameters, up to but not including the
+  // rest parameter index (if the function has rest parameters), i.e. it
+  // says 2 for
+  //
+  //   function foo(a, b) { ... }
+  //
+  // and
+  //
+  //   function foo(a, b, ...c) { ... }
+  //
+  // but for
+  //
+  //   function foo(a, b, c = 1) { ... }
+  //
+  // we return 3 here.
+  int num_parameters() const {
+    return has_rest_parameter() ? params_.length() - 1 : 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_;
   }
 
   bool has_rest_parameter() const { return rest_index_ >= 0; }
 
@@ skipping 398 matching lines @@
 
   // For tracking which classes are declared consecutively. Needed for strong
   // mode.
   int class_declaration_group_start_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_SCOPES_H_