@Metric/@metricmethod break zope.interface validation of method signatures

[jamadden]

This surprised me today. I changed an interface signature and expected test failures to alert me that the implementations no longer correctly implemented the method (because I hadn't updated their signatures yet). But that didn't happen. It turns out that the call_with_metric wrapper that's being returned from the decorator takes *args, **kwargs and that's enough to break signature introspection as far as zope.interface is concerned.

Interestingly, it doesn't break signature display as far as IPython is concerned.

I'm not sure there's anything much we can do here other than document this.

[jamadden]

We could add an environment variable that causes the decorator to become a no-op and return the function without wrapping it.