Copying Mike. More thoughts inline.

On 2/26/19 9:24 AM, Herve Beraud wrote:
> Hi,
>
> Just a heads up that the latest version of dogpile (0.7.0 onwards)
> have become incompatible with oslo.cache.  This is causing a few
> issues for jobs.  It's a little complex due to functional code and many
> decorated functions.
>
> The error you will see is:
> /
> /
>
> /oslo_cache.//tests.test_//cache.CacheRegi//onTest.//test_function_//key_generator_//with_kwargs
> -------//-------//-------//-------//-------//-------//-------//-------//-------//-------//-------//------/
>
> //
>
> /Captured traceback:
> ~~~~~~~~~~~~~~~~~~~
>      b'Traceback (most recent call last):'
>      b' File "/tmp/oslo.//cache/oslo_//cache/tests///test_cache.//py",
> line 324, in test_function_//key_generator_//with_kwargs'
>      b' value=self.//test_value)//'
>      b' File
> "/tmp/oslo.//cache/.//tox/py37///lib/python3.//7/site-//packages///testtools///testcase.//py",
> line 485, in assertRaises'
>      b' self.assertThat//(our_callable, matcher)'
>      b' File
> "/tmp/oslo.//cache/.//tox/py37///lib/python3.//7/site-//packages///testtools///testcase.//py",
> line 498, in assertThat'
>      b' raise mismatch_error'
>      b'testtools//.matchers.//_impl.MismatchE//rror: <function
> CacheRegionTest//._get_cacheable//_function.//<locals>//.cacheable_//function
> at 0x7fec3f795400> returned
> <oslo_cache.//tests.test_//cache.TestProxy//Value object at
> 0x7fec3f792550>'/
>
>
> The problem appear since we uncap dogpile.cache on oslo.cache:
> https://github.com/openstack/oslo.cache/commit/62b53099861134859482656dc92db81243b88bd9
>
> The following unit test fail since we uncap dogpile =>
> https://github.com/openstack/oslo.cache/blob/master/oslo_cache/tests/test_cache.py#L318
>
> The problem was introduced by:
> https://gerrit.sqlalchemy.org/#/c/sqlalchemy/dogpile.cache/+/996/
>
> Your main issue on oslo.cache side is that keyword arguments are
> tranformed in positionnal arguments when we use
> dogpile.cache.region.cache_on_arguments.
>
> I've try to revert the changes introduced by the previous dogpile.cache
> change and everything works fine on the oslo.cache side when changes was
> reverted (reverted to revision
> https://github.com/sqlalchemy/dogpile.cache/blob/2762ada1f5e43075494d91c512f7c1ec68907258/dogpile/cache/region.py).
>
> The expected behavior is that dogpile.cache.util.function_key_generator
> raise a ValueError if **kwargs founds, but our kwargs is empty and our
> `value=self.test_value was` is recognized as a positionnal argument.
> Our unit test looking for an assertRaise(ValueError) on cachable
> decorated function when we pass kwargs but it doesn't happen due to
> empty kwargs.
>
> For these reasons we guess that is an dogpile.cache issue and not an
> oslo.cache issue due to the changes introduced by `decorator` module.
>
> The following are related:
>
> -
> https://github.com/openstack/oslo.cache/blob/master/oslo_cache/tests/test_cache.py#L318
> : unit test where the problem occure
> - https://review.openstack.org/#/c/638788/ : possible fix but we don't
> think that is the right way
> - https://review.openstack.org/#/c/638732/ : possible remove of the unit
> test who fail

As I noted in the reviews, I don't think this is something we should
have been testing in oslo.cache in the first place. The failing test is
testing the dogpile interface, not the oslo.cache one. I've seen no
evidence that oslo.cache is doing anything wrong here, so our unit tests
are clearly testing something that should be out of scope.

And to be clear, I'm not even sure this is a bug in dogpile. It may be a
happy side-effect of the decorator change that the regular decorator now
works for kwargs too. I don't know dogpile well enough to make a
definitive statement on that though. Hence cc'ing Mike. :-)

>
> The issue is being tracked in:
>
> https://bugs.launchpad.net/oslo.cache/+bug/1817032
>
> If some dogpile expert can take a look and send feedback on this thread
> you are welcome.
>
> Thanks,
>
> --
> Hervé Beraud
> Senior Software Engineer
> Red Hat - Openstack Oslo
> irc: hberaud
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