Mutation trampoline fixes #375
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Previously, mutmut would fail on a function call that contains the kwarg `orig` or `mutants`, e.g. `foo(orig=123)`. The trampoline setup would try to call `_mutmut_trampoline(foo_orig, foo_mutants, *args, **kwargs)` which now has the argument `orig` twice (once as a positional arg and once as a kwarg) and thus raise a TypeError.
Previously, mutated class methods were always killed, because no `self` arg was passed to their calls and thus raised a TypeError for invalid number of arguments. The class methods in the mutants dict are stored without reference to any class instance and therefore not bound to any instance. We need to pass the `self` arg explicitly in those cases. Note that the call to the original method is a bound method (the method is looked up via the `self` parameter), thus we do not pass the `self` arg in this case.
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While testing I found two errors in the mutation setup:
The same-args bug only occurs when calling methods with the keywords
origormutants. e.g. iffoo(orig=123)was called somewhere. This already fails at the clean test run, so nobody reporting it as an issue seems like no one uses these kwargs. I only noticed when running mutmut on mutmut self.The self-parameter bug killed all class method mutations, because the mutations did not receive
selfas an argument and are not bound to any class instance. Unluckily, it worked for the original method, because the original method is passed as a bound method and does not requireselfto be passed as an argument, so the clean tests run did not notice this error. Fixing this bug will result in a decent amount of new survived mutants for projects that use classes.The commit messages contain more technical details. For the self-parameter bug, I will submit an E2E snapshot test in the next days that would detect a regression that accidentally introduces it again.