Re: [PATCH v2 6/7] CI: Stop building docs on centos8

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Feb 14, 2023 at 09:52:44PM +0100, Paolo Bonzini wrote:
> Il mar 14 feb 2023, 18:26 Kevin Wolf <kwolf@redhat.com> ha scritto:
> 
> > Am 14.02.2023 um 15:03 hat Paolo Bonzini geschrieben:
> > > In the case of Python the issue is not the interpreter per se, though
> > > there are a couple new feature in Python 3.7 that are quite nice (for
> > > example improved data classes[1] or context variables[2]). The main
> > > problem as far as I understood (and have seen in my experience) is
> > > linting tools. New versions fix bugs that caused false positives, but
> > > also become more strict at the same time. The newer versions at the
> > > same time are very quick at dropping support for old versions of
> > > Python; while older versions sometimes throw deprecation warnings on
> > > new versions of Python. This makes it very hard to support a single
> > > version of, say, mypy that works on all versions from RHEL8 and SLE15
> > > to Fedora 38 and Ubuntu 23.04.
> >
> > Why do we have to support a single version of mypy? What is wrong with
> > running an old mypy version with old Python version, and a newer mypy
> > with newer Python versions?
> >
> > Sure, they will complain about different things, but it doesn't feel
> > that different from supporting multiple C compilers in various versions.
> >
> 
> It's more like having to support only C++03 on RHEL 8 and only C++20 in
> Fedora 37, without even being able to use a preprocessor.
> 
> For example old versions might not understand some type annotations and
> will fail mypy altogether, therefore even with newer versions you can't
> annotate the whole source and have to fall back to non-strict mode.

In terms of back compatibility, is there a distinction to be
made between mypy compat and the python runtime compat ?

If we add annotations wanted by new mypy, and old mypy doesn't
understand them, that's not a huge problem. We can simply declare
that we don't support old mypy, and skip the validation tests if
old mypy is installed. The mypy results are targetted at upstream
maintainers primarily, not people consuming QEMU, unless they are
backporting huge amounts of code and need to validate it. IOW it
should be sufficient to test once with an arbitrary version of
mypy of our choosing.

If we add annotations wanted by new mypy, and old python runtime
barfs, then that's a significant problem, which would require us
to either bump the min python or avoid the new mypy annotations.



The same could be asked for the other linting tools we use like
pylint / flake8. Is it sufficient to declare a min versions for
those tools and skip the tests if not satisfied, while still
retaining ability to execute the code on 3.6 ?

Or are there some core python runtime features we also want to
take advantage of at the same time ?


With regards,
Daniel
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