Make length property return useful values for DOM bindings functions

Source/bindings/scripts/CodeGeneratorV8.pm

Index: Source/bindings/scripts/CodeGeneratorV8.pm
diff --git a/Source/bindings/scripts/CodeGeneratorV8.pm b/Source/bindings/scripts/CodeGeneratorV8.pm
index dbb1c56a26978f9f8378e0c343b7f91931113a41..d8eeae40825a3cced5ca7a541551719d5c75befe 100644
--- a/Source/bindings/scripts/CodeGeneratorV8.pm
+++ b/Source/bindings/scripts/CodeGeneratorV8.pm
@@ -2139,6 +2139,31 @@ END
     push(@implContentInternals, "\n");
 }
 
+sub GetConstructorLength
+{
+    my $interface = shift;
+
+    my $numberOfConstructorParameters = $interface->extendedAttributes->{"ConstructorParameters"};
+    if (!defined $numberOfConstructorParameters) {
+        if ($codeGenerator->IsConstructorTemplate($interface, "Event")) {
+            $numberOfConstructorParameters = 2;
+        } elsif ($codeGenerator->IsConstructorTemplate($interface, "TypedArray")) {
+            $numberOfConstructorParameters = 1;
+        } elsif ($interface->extendedAttributes->{"Constructor"}) {
+            my @constructors = @{$interface->constructors};
+            $numberOfConstructorParameters = 255;
+            foreach my $constructor (@constructors) {
+                my $currNumberOfParameters = @{$constructor->parameters};
+                if ($currNumberOfParameters < $numberOfConstructorParameters) {
+                    $numberOfConstructorParameters = $currNumberOfParameters;

[haraken, 2013/04/16 00:29:31]

I'm not sure if this is correct. Per the spec, it looks like you have to report
# of mandatory arguments (i.e. not including optional parameters).
http://www.w3.org/TR/WebIDL/#es-interface-call

[do-not-use, 2013/04/16 07:26:23]

Sorry, could you point me to the part where it says we should only count
mandatory arguments? I cannot find it. What I could find at the link you
provided is:

"""
 Interface objects for interfaces declared with a [Constructor] extended
attribute MUST have a property named “length” with attributes { [[Writable]]:
false, [[Enumerable]]: false, [[Configurable]]: false } whose value is a Number
determined as follows:

    Let id be the identifier of interface I.
    Initialize S to the effective overload set for constructors with identifier
id on interface I and with argument count 0.
    Return the maximum argument list length of the constructors in the entries
of S.
"""

If I understand correctly, we need to select the maximum argument list length
among all the constructors, counting optional arguments. My patch is actually
currently doing the opposite (selecting the minimum argument list length).

[do-not-use, 2013/04/16 09:39:20]

Actually, the latest Editor Draft matches the behavior you were mentioning:
http://dev.w3.org/2006/webapi/WebIDL/#es-interface-call

This was changed about 6 month ago. So I guess we should follow the latest
editor draft and use the shortest argument list in the effective overload set
instead? This also means that optional arguments are not counted due to the
definition of an "effective overload set"
(http://dev.w3.org/2006/webapi/WebIDL/#dfn-effective-overload-set).

+                }
+            }
+        }
+    }
+
+    return $numberOfConstructorParameters;
+}
+
 sub GenerateConstructorCallback
 {
     my $interface = shift;
@@ -3048,10 +3073,11 @@ END
         if ($function->signature->extendedAttributes->{"PerWorldBindings"}) {
             $methodForMainWorld = "${interfaceName}V8Internal::${name}MethodCallbackForMainWorld";
         }
+        my $numParams = @{$function->parameters};
         my $conditionalString = $codeGenerator->GenerateConditionalString($function->signature);
         push(@implContent, "#if ${conditionalString}\n") if $conditionalString;
         push(@implContent, <<END);
-    {"$name", ${interfaceName}V8Internal::${name}MethodCallback, ${methodForMainWorld}},
+    {"$name", ${interfaceName}V8Internal::${name}MethodCallback, ${methodForMainWorld}, ${numParams}},
 END
         push(@implContent, "#endif\n") if $conditionalString;
         $num_callbacks++;
@@ -3186,6 +3212,8 @@ END
 
     if (IsConstructable($interface)) {
         push(@implContent, "    desc->SetCallHandler(${v8InterfaceName}::constructorCallback);\n");
+        my $constructorLength = GetConstructorLength($interface);
+        push(@implContent, "    desc->SetLength(${constructorLength});\n") if defined $constructorLength;

[haraken, 2013/04/16 00:29:31]

'if defined' is not needed.

     }
 
     if ($access_check or @enabledAtRuntimeAttributes or @normalFunctions or $has_constants) {