[gentoo-dev] Re: [RFC] dev-python/namespace-* retirement plan

[Arthur Zamarin]

On 09/04/2022 18.20, Michał Górny wrote:
> Hi, everyone.
>
> TL;DR I think I came up with a feasible plan towards cleanly removing
> dev-python/namespace-* packages that aren't technically needed anymore
> with modern versions of Python.
>
>
> What are namespace packages?  Let's take "zope" as an example.
> Normally, various subpackages like "zope.interface" and
> "zope.configuration" would have all to be present in a single directory,
> that is inside the "zope" package.  However, if "zope" is made a
> namespace package, its subpackages can be loaded from different
> locations.  Notably, in order to test zope.configuration prior to
> installing it, we load it from build tree but its dependency
> zope.interface from system site-packages.
>
> Historically, for this to work, the "zope/__init__.py" had to specify
> some magic incantations.  On Gentoo, we've added dev-python/namespace-*
> that installed these magical "__init__.py" files and made all
> subpackages (e.g. dev-python/zope-*) depend on it.
>
> However, Python 3.3 introduced PEP 420 implicit namespaces that made
> magical incantations unnecessary -- if "zope" didn't include
> "__init__.py", it was implicitly treated as a namespace.  Unfortunately,
> there were some interoperability issues between the two kinds of magical
> incantations and implicit namespaces.  So while we were able to retire
> pkgutil-style namespaces, setuptools-style namespaces remained.
>
> I think we can change that now.
>
>
> I've done some experiments, particularly with dev-python/zope-interface
> and dev-python/zope-configuration.  If nobody finds a problem with this
> solution, I think we can aim to bump all packages relying on namespaces
> and retire them in 1-2 months.
>
> The rough idea is to remove RDEP on dev-python/namespace-* from
> the package, and updating python_test to use a temporary pkgutil-style
> incantation (yes, for setuptools-style packages), e.g.:
>
> ```
> python_compile() {
> 	distutils-r1_python_compile
> 	find "${BUILD_DIR}" -name '*.pth' -delete || die
> }
>
> python_test() {
> 	cd "${BUILD_DIR}/install$(python_get_sitedir)" || die
> 	# this is needed to keep the tests working while
> 	# dev-python/namespace-zope is still installed
> 	cat > zope/__init__.py <<-EOF || die
> 		__path__ = __import__('pkgutil').extend_path(__path__,
> __name__)
> 	EOF
> 	eunittest
> 	rm zope/__init__.py || die
> }
> ```

I quite like that we make the "hack" more local, just in test phase. But
I think this code is quite error prone, and an easy mistake can be made
if someone copies it incorrectly.

Is it possible to add an eclass function to auto create and cleanup this
file, and all I need to do is to pass it the correct namespace ("zope"
in above example)?

Also, by using a common function name, it would be easy to fix it if we
did a mistake and find all consumers when we feel safe to cleanup this code.

One point of failure for this function is how to do the auto cleanup? I
was thinking using environment variables to hold our added magic names,
which is created before `python_test` call and cleans after it is done.
I really prefer if we could call it during prepare phase (so we can
still use auto generated d_e_t calls).

> ...
>
> WDYT?
>


-- 
Arthur Zamarin
arthurzam@g.o
Gentoo Linux developer (Python, GURU, Arch Teams)