Proper dispatch in the presence of optional arguments.

lib/dom/scripts/systemnative.py

 #!/usr/bin/python
 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 """This module provides shared functionality for the systems to generate
 native binding from the IDL database."""
 
 import emitter
 import os
@@ skipping 637 matching lines @@
     # TODO: Optimize the dispatch to avoid repeated checks.
     if len(operations) > 1:
       for operation in operations:
         for position, argument in enumerate(operation.arguments):
           if self._IsArgumentOptionalInWebCore(operation, argument):
             GenerateChecksAndCall(operation, position)
         GenerateChecksAndCall(operation, len(operation.arguments))
       body.Emit('    throw "Incorrect number or type of arguments";\n');
     else:
       operation = operations[0]
+      argument_count = len(operation.arguments)
       for position, argument in list(enumerate(operation.arguments))[::-1]:
         if self._IsArgumentOptionalInWebCore(operation, argument):
-          check = '%s === _null' % argument_names[position]
-          GenerateCall(operation, position, [check])
-      GenerateCall(operation, len(operation.arguments), [])
+          check = '%s !== _null' % argument_names[position]
+          # argument_count instead of position + 1 is used here to cover one
+          # complicated case.  Consider foo(x, [Optional] y, [Optional=DefaultIsNullString] z)

[podivilov, 2012/08/21 13:46:57]

I think it's exactly the optional in the middle problem we had previously since
[Optional=DefaultIsNullString] is mandatory in dart (they finally found a
loophole to introduce opt in the middle again :). Could you please clarify the
comment to state it more explicitly?

Another problem is that foo(x, y) will invoke fooNativeCallback(x, y, _null)
instead of fooNativeCallback(x, y, null).

[Anton Muhin, 2012/08/21 18:14:34]

Yes, this _null/null distinction is another of problems I spotted in our current
code.

Updating a description...

On 2012/08/21 13:46:57, podivilov wrote:

+          # (as of now it's modelled after HTMLMediaElement.webkitAddKey).
+          # y is optional in WebCore, while z is not.
+          # In this case, if y !== _null, we'd like to emit foo(x, y, z) invocation, not
+          # foo(x, y).
+          GenerateCall(operation, argument_count, [check])
+          argument_count = position
+      GenerateCall(operation, argument_count, [])
 
   def SecondaryContext(self, interface):
     pass
 
   def _GenerateOperationNativeCallback(self, operation, arguments, cpp_callback_name):
     webcore_function_name = operation.ext_attrs.get('ImplementedAs', operation.id)
     function_expression = self._GenerateWebCoreFunctionExpression(webcore_function_name, operation)
     self._GenerateNativeCallback(
         cpp_callback_name,
         not operation.is_static,
@@ skipping 263 matching lines @@
     parent_interface = _FindInHierarchy(database, parent_interface, test)
     if parent_interface:
       return parent_interface
 
 def _ToWebKitName(name):
   name = name[0].lower() + name[1:]
   name = re.sub(r'^(hTML|uRL|jS|xML|xSLT)', lambda s: s.group(1).lower(),
                 name)
   return re.sub(r'^(create|exclusive)', lambda s: 'is' + s.group(1).capitalize(),
                 name)