Adaption of web2.iweb interfaces is broken

[wsanchez]

As of r18455, adaption of web2.iweb interfactes is broken in that it no longer raises TypeError when adaptions fails and instead returns None.

A change to SpecialAdaptInterfaceClass.__call__() appears to be the cause.

[wsanchez]

Perhaps something more like:

# Is there a better way to do this than this funky extra class?
NotSpecified = object()
class SpecialAdaptInterfaceClass(interface.InterfaceClass):
    # A special adapter for IResource to handle the extra step of adapting
    # from IOldNevowResource-providing resources.
    def __call__(self, other, alternate=NotSpecified):
        if alternate == NotSpecified:
            try:
                return super(SpecialAdaptInterfaceClass, self).__call__(other)
            except TypeError:
                pass
        else:
            result = super(SpecialAdaptInterfaceClass, self).__call__(other, alternate)
            if result is not alternate:
                return result
        
        if alternate == NotSpecified:
            return IOldNevowResource(other)
        result = IOldNevowResource(other, alternate)
        if result is not alternate:
            return IResource(result)
        return alternate
IResource.__class__ = SpecialAdaptInterfaceClass

[exarkun]

Ready for review in transitive-adaption-2199

[therve]

Looks good, greatly improves test coverage. I was only wondering if the tests wouldn't be better in test_compat than in test_server. Anyway it should be merged.

[exarkun]

(In [18666]) Merge transitive-adaption-2199

Author: exarkun Reviewer: therve Fixes #2199

Add tests for various adaption behaviors related to IResource and fix the implementation of IResource.class.call to make these new tests pass.