Make length property return useful values for DOM bindings functions

Source/bindings/scripts/CodeGeneratorV8.pm

 # Copyright (C) 2005, 2006 Nikolas Zimmermann <zimmermann@kde.org>
 # Copyright (C) 2006 Anders Carlsson <andersca@mac.com>
 # Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
 # Copyright (C) 2006 Alexey Proskuryakov <ap@webkit.org>
 # Copyright (C) 2006 Apple Computer, Inc.
 # Copyright (C) 2007, 2008, 2009, 2012 Google Inc.
 # Copyright (C) 2009 Cameron McCormack <cam@mcc.id.au>
 # Copyright (C) Research In Motion Limited 2010. All rights reserved.
 # Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
 # Copyright (C) 2012 Ericsson AB. All rights reserved.
@@ skipping 2185 matching lines @@
     if ($raisesExceptions) {
         $code .= "    fail:\n";
         $code .= "    return setDOMException(ec, args.GetIsolate());\n";
     }
 
     $code .= "}\n";
     $code .= "\n";
     AddToImplContentInternals($code);
 }
 
+# The Web IDL specification states that Interface objects for interfaces MUST have a property named
+# "length" that returns the length of the shortest argument list of the entries in the effective
+# overload set for constructors. In other words, use the lowest number of mandatory arguments among
+# all constructors.
+sub GetInterfaceLength
+{
+    my $interface = shift;
+
+    my $leastNumMandatoryParams = 0;
+    if ($codeGenerator->IsConstructorTemplate($interface, "Event") || $codeGenerator->IsConstructorTemplate($interface, "TypedArray")) {
+        $leastNumMandatoryParams = 1;
+    } elsif ($interface->extendedAttributes->{"Constructor"} || $interface->extendedAttributes->{"CustomConstructor"}) {
+        my @constructors = @{$interface->constructors};
+        my @customConstructors = @{$interface->customConstructors};
+        $leastNumMandatoryParams = 255;
+        foreach my $constructor (@constructors, @customConstructors) {
+            my ($numMandatoryParams, $parametersCheck) = GenerateFunctionParametersCheck($constructor);
+            $leastNumMandatoryParams = $numMandatoryParams if ($numMandatoryParams < $leastNumMandatoryParams);
+        }
+    }
+
+    return $leastNumMandatoryParams;
+}
+
 sub GenerateConstructorCallback
 {
     my $interface = shift;
 
     my $interfaceName = $interface->name;
     my $code = "";
     $code .= "v8::Handle<v8::Value> V8${interfaceName}::constructorCallback(const v8::Arguments& args)\n";
     $code .= "{\n";
     $code .= GenerateFeatureObservation($interface->extendedAttributes->{"MeasureAs"});
     $code .= GenerateConstructorHeader();
@@ skipping 957 matching lines @@
         next if !IsStandardFunction($interface, $function);
         if (!$has_callbacks) {
             $has_callbacks = 1;
             $code .= "static const V8DOMConfiguration::BatchedMethod ${v8InterfaceName}Methods[] = {\n";
         }
         my $name = $function->signature->name;
         my $methodForMainWorld = "0";
         if ($function->signature->extendedAttributes->{"PerWorldBindings"}) {
             $methodForMainWorld = "${interfaceName}V8Internal::${name}MethodCallbackForMainWorld";
         }
+        # numMandatoryParams is used to set the "length" property of the Function object.
+        my ($numMandatoryParams, $parametersCheck) = GenerateFunctionParametersCheck($function);
         my $conditionalString = $codeGenerator->GenerateConditionalString($function->signature);
         $code .= "#if ${conditionalString}\n" if $conditionalString;
         $code .= <<END;
-    {"$name", ${interfaceName}V8Internal::${name}MethodCallback, ${methodForMainWorld}},
+    {"$name", ${interfaceName}V8Internal::${name}MethodCallback, ${methodForMainWorld}, ${numMandatoryParams}},
 END
         $code .= "#endif\n" if $conditionalString;
         $num_callbacks++;
     }
     $code .= "};\n\n"  if $has_callbacks;
     AddToImplContent($code);
 
     # Setup constants
     my $has_constants = 0;
     my @constantsEnabledAtRuntime;
@@ skipping 117 matching lines @@
 END
     }
 
     AddToImplIncludes("wtf/UnusedParam.h");
     $code .= <<END;
     UNUSED_PARAM(defaultSignature); // In some cases, it will not be used.
 END
 
     if (IsConstructable($interface)) {
         $code .= "    desc->SetCallHandler(${v8InterfaceName}::constructorCallback);\n";
+        my $interfaceLength = GetInterfaceLength($interface);
+        $code .= "    desc->SetLength(${interfaceLength});\n";
     }
 
     if ($access_check or @enabledAtRuntimeAttributes or @normalFunctions or $has_constants) {
         $code .=  <<END;
     v8::Local<v8::ObjectTemplate> instance = desc->InstanceTemplate();
     v8::Local<v8::ObjectTemplate> proto = desc->PrototypeTemplate();
     UNUSED_PARAM(instance); // In some cases, it will not be used.
     UNUSED_PARAM(proto); // In some cases, it will not be used.
 END
     }
@@ skipping 1398 matching lines @@
 
 sub GetPassRefPtrType
 {
     my $v8InterfaceName = shift;
 
     my $angleBracketSpace = $v8InterfaceName =~ />$/ ? " " : "";
     return "PassRefPtr<${v8InterfaceName}${angleBracketSpace}>";
 }
 
 1;