SystemError when passing an empty byte string in Python 3.x

[reaperhulk]

Under Python 3.x with pytest 2.8.1

import pytest

@pytest.mark.parametrize("message", [b""])
def test_broken(message):
    pass

causes a SystemError during the call to codecs.escape_encode inside _escape_bytes. This was introduced in commit e106367, but is really a CPython bug as codecs.escape_encode(b'') should not cause a SystemError. That said, pytest probably needs to work around the bug for now.

Stack trace:

../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/runner.py:149: in __init__
    self.result = func()
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/main.py:437: in _memocollect
    return self._memoizedcall('_collected', lambda: list(self.collect()))
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/main.py:317: in _memoizedcall
    res = function()
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/main.py:437: in <lambda>
    return self._memoizedcall('_collected', lambda: list(self.collect()))
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:578: in collect
    return super(Module, self).collect()
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:432: in collect
    res = self.makeitem(name, obj)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:444: in makeitem
    collector=self, name=name, obj=obj)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/vendored_packages/pluggy.py:724: in __call__
    return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/vendored_packages/pluggy.py:338: in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/vendored_packages/pluggy.py:333: in <lambda>
    _MultiCall(methods, kwargs, hook.spec_opts).execute()
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/vendored_packages/pluggy.py:595: in execute
    return _wrapped_call(hook_impl.function(*args), self.execute)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/vendored_packages/pluggy.py:249: in _wrapped_call
    wrap_controller.send(call_outcome)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:307: in pytest_pycollect_makeitem
    res = list(collector._genfunctions(name, obj))
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:464: in _genfunctions
    self.ihook.pytest_generate_tests(metafunc=metafunc)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/vendored_packages/pluggy.py:724: in __call__
    return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/vendored_packages/pluggy.py:338: in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/vendored_packages/pluggy.py:333: in <lambda>
    _MultiCall(methods, kwargs, hook.spec_opts).execute()
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/vendored_packages/pluggy.py:596: in execute
    res = hook_impl.function(*args)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:217: in pytest_generate_tests
    metafunc.parametrize(*marker.args, **marker.kwargs)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:994: in parametrize
    ids = idmaker(argnames, argvalues, idfn)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:1108: in idmaker
    for valindex, valset in enumerate(argvalues)]
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:1108: in <listcomp>
    for valindex, valset in enumerate(argvalues)]
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:1103: in _idvalset
    for val, argname in zip(valset, argnames)]
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:1103: in <listcomp>
    for val, argname in zip(valset, argnames)]
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:1082: in _idval
    return _escape_bytes(val)
../../.virtualenvs/crypto3/lib/python3.4/site-packages/_pytest/python.py:1058: in _escape_bytes
    encoded_bytes, _ = codecs.escape_encode(val)
E   SystemError: Objects/bytesobject.c:2828: bad argument to internal function

[The-Compiler]

I reported the bug upstream as issue25271.