ImportWarning: can't resolve package from __spec__ or __package__

[Callek]

Related to #3061

I'm hitting this in @mozilla-releng/addonscript with pytest 4.0 on travis (locally reproduced back to pytest 3.7.3) --

Travis Log: https://travis-ci.org/mozilla-releng/addonscript/builds/457101239

Local pytest extensions

• pytest-asyncio
• pytest-cov
• pytest-mock

I'm also getting no traceback at all..

====================================================== warnings summary ======================================================
.tox/py36/lib/python3.6/importlib/_bootstrap.py:219
  /home/callek/mozilla/git/addonscript/.tox/py36/lib/python3.6/importlib/_bootstrap.py:219: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
    return f(*args, **kwds)

-- Docs: https://docs.pytest.org/en/latest/warnings.html
=========================================== 64 passed, 1 warnings in 0.61 seconds ============================================
py36 runtests: commands[3] | coverage html
py36 runtests: commands[4] | flake8

[Callek]

I should note that I've been using py.test -Wd ... as my invocation for a quite a while and this is the first I've seen it (the upgrade of pytest)

[RonnyPfannschmidt]

thanks for the report - i vaguely suspect we need to do some extra work to do the correct thing in the assertion rewriter

[asottile]

Here's the stacktrace:

$ pytest --maxfail 1 -Werror
============================= test session starts ==============================
platform linux -- Python 3.6.6, pytest-4.0.0, py-1.7.0, pluggy-0.8.0 -- /tmp/addonscript/venv/bin/python3
cachedir: .pytest_cache
rootdir: /tmp/addonscript, inifile: tox.ini
plugins: mock-1.10.0, asyncio-0.9.0
collecting ... 
==================================== ERRORS ====================================
________________ ERROR collecting addonscript/test/test_api.py _________________
addonscript/test/test_api.py:4: in <module>
    import aiohttp
venv/lib/python3.6/site-packages/aiohttp/__init__.py:5: in <module>
    from . import hdrs  # noqa
venv/lib/python3.6/site-packages/aiohttp/hdrs.py:6: in <module>
    from multidict import istr
venv/lib/python3.6/site-packages/multidict/__init__.py:23: in <module>
    from ._multidict import (MultiDictProxy,
multidict/_multidict.pyx:9: in init multidict._multidict
    ???
E   ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
=========================== 1 error in 0.04 seconds ============================

Running this outside of `pytest:

$ python -Wonce -c 'import multidict'
/tmp/addonscript/venv/lib/python3.6/site.py:165: DeprecationWarning: 'U' mode is deprecated
  f = open(fullname, "rU")
_frozen_importlib:219: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__

This isn't an issue with pytest but with multidict

[asottile]

I've taken some time and figured out what multidict needs to do to fix this: aio-libs/multidict#304

closing this! Thanks for the issue, this was fun 🎉

[asottile]

@Callek btw, if you upgrade to multidict==4.5.0 that error is fixed