HMock with DefaultSignatures

In the Mocking FileStatus blog entry, I demonstrated a way to mock the unix/unix-compat file status API. My example used the DefaultSignatures extension to provide default implementations of methods for MonadIO monads. I am writing HMock tests today and discovered that makeMockable is incompatible with the DefaultSignatures extension.

I created an issue right before lunch, and I decided to go ahead and implement a fix after lunch. The code iterates over the declarations within a class declaration and throws an error if any are not signatures for methods that can be mocked. It was easy to fix by filtering the member declarations before they are processed, which allows declarations of specific types (such as DefaultSigD) to be ignored.

The Mocking FileStatus code does not work with the current release of HMock due to this issue, but the issue will (hopefully) soon be fixed with a pull request.