pytest-xdist 2 support

[dmtucker]

There are some breaking changes: https://github.com/pytest-dev/pytest-xdist/blob/1d08799c82f94d7c2c32a8131945babc4a580ae0/CHANGELOG.rst#pytest-xdist-200-2020-08-12

$ venv/bin/pytest --mypy --verbose -n auto demo
================================================ test session starts =================================================
platform linux -- Python 3.8.2, pytest-6.0.1, py-1.9.0, pluggy-0.13.1 -- /home/dtux/Projects/pytest-mypy/venv/bin/python
cachedir: .pytest_cache
Using --randomly-seed=1597766100
rootdir: /home/dtux/Projects/pytest-mypy
plugins: xdist-2.0.0, forked-1.3.0, randomly-2.1.1, pylint-0.17.0, cov-2.5.1, mypy-0.6.3.dev21+gbf78e22.d20200818
[gw0] linux Python 3.8.2 cwd: /home/dtux/Projects/pytest-mypy
gw0 C / gw1 I / gw2 I / gw3 IINTERNALERROR> Traceback (most recent call last):
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/_pytest/main.py", line 238, in wrap_session
INTERNALERROR>     config.hook.pytest_sessionstart(session=session)
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/hooks.py", line 286, in __call__
INTERNALERROR>     return self._hookexec(self, self.get_hookimpls(), kwargs)
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/manager.py", line 93, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/manager.py", line 84, in <lambda>
INTERNALERROR>     self._inner_hookexec = lambda hook, methods, kwargs: hook.multicall(
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/callers.py", line 208, in _multicall
INTERNALERROR>     return outcome.get_result()
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/callers.py", line 80, in get_result
INTERNALERROR>     raise ex[1].with_traceback(ex[2])
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/callers.py", line 187, in _multicall
INTERNALERROR>     res = hook_impl.function(*args)
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/xdist/dsession.py", line 78, in pytest_sessionstart
INTERNALERROR>     nodes = self.nodemanager.setup_nodes(putevent=self.queue.put)
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/xdist/workermanage.py", line 65, in setup_nodes
INTERNALERROR>     return [self.setup_node(spec, putevent) for spec in self.specs]
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/xdist/workermanage.py", line 65, in <listcomp>
INTERNALERROR>     return [self.setup_node(spec, putevent) for spec in self.specs]
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/xdist/workermanage.py", line 73, in setup_node
INTERNALERROR>     node.setup()
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/xdist/workermanage.py", line 260, in setup
INTERNALERROR>     self.config.hook.pytest_configure_node(node=self)
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/hooks.py", line 286, in __call__
INTERNALERROR>     return self._hookexec(self, self.get_hookimpls(), kwargs)
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/manager.py", line 93, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/manager.py", line 84, in <lambda>
INTERNALERROR>     self._inner_hookexec = lambda hook, methods, kwargs: hook.multicall(
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/callers.py", line 208, in _multicall
INTERNALERROR>     return outcome.get_result()
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/callers.py", line 80, in get_result
INTERNALERROR>     raise ex[1].with_traceback(ex[2])
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/venv/lib/python3.8/site-packages/pluggy/callers.py", line 187, in _multicall
INTERNALERROR>     res = hook_impl.function(*args)
INTERNALERROR>   File "/home/dtux/Projects/pytest-mypy/src/pytest_mypy.py", line 66, in pytest_configure_node
INTERNALERROR>     node.slaveinput['_mypy_results_path'] = \
INTERNALERROR> AttributeError: 'WorkerController' object has no attribute 'slaveinput'

[leorochael]

PR #101 fixes this issue.