[Distutils] Finishing up PEP 517

[Paul Moore]

On 28 June 2017 at 05:29, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On 28 June 2017 at 13:43, Nathaniel Smith <njs at pobox.com> wrote:
>> I would say that there's only one required path, which is in-place.
>> (But the tree that they do the in-place build in might have a more or
>> less complicated history). It worries me that you seem to think that
>> build_sdist and build_wheel should be coupled like this... this
>> proliferation of cases and the reification of "out of tree builds" as
>> a special thing that's different from an in-tree build in a temporary
>> tree is already what worried me about prepare_wheel_input_files, and
>> now it seems to be spreading :-).
>
> I don't know what additional coupling you're seeing: the only coupling
> is that building a wheel directly from a VCS source tree and first
> exporting an sdist and then building a wheel from that *must give the
> same result* (modulo any problems related to reproducible builds, or
> the lack thereof). If a project can't meet that expectation, then
> their sdist generation is broken, since it clearly isn't exporting the
> necessary content to actually build the project properly.
>
> If you weren't aware of that inherent coupling, and are surprised by
> the fact that it's a constraint on publishing useful sdists, then I'd
> consider it a good thing that PEP 517 is now making it more explicit.

Note that the whole concept of "out of tree builds" is not something
theoretical - it comes directly from pip's requirement to be able to
do clean builds. So saying that tree->sdist->unpacked sdist is "just
another in-place build of a different tree" is missing the point,
which is that we need a mechanism to produce an effectively identical,
in the sense that it must result in the same wheel, copy of a tree -
and because we chose the sdist as the route for that, there are
constraints on the contents of a sdist.

I view those constraints as pretty much self evident, as I would be
extremely surprised if I had a source tree of *any* form for a
project, and I build a sdist from it and gave it to a friend, and when
we both built wheels and installed them, we had different installed
copies of the project.

The alternative would be to have a separate "produce a copy of this
tree that builds the same wheel" hook. And I thought we already went
round that loop, which is how we ended up deciding that the sdist was
our approach...

Paul