[Distutils] status check on PEP 517

[Daniel Holth]

I think the proposal is that flit depends on click depends on flit and
neither one has a wheel and must be built from sdists. Then you have a
circular build problem. So don't do that. I put this in the same category
as accidentally conflicting with a stdlib module; it is confusing when it
happens but it's also fairly avoidable.

On Sat, Jul 29, 2017, 17:38 Alex Grönholm <alex.gronholm at nextday.fi> wrote:

> Donald Stufft kirjoitti 29.07.2017 klo 23:47:
>
>
> On Jul 29, 2017, at 12:46 PM, Nathaniel Smith <njs at pobox.com> wrote:
>
> I guess the most obvious example of when this would occur is: suppose
> click switches to using flit for builds, and then flit switches to using
> click for command line parsing. Now there's a bit of a chicken and egg
> problem where 'pip install click' will end up importing flit with the click
> source tree on the path, and this tree of course contains a directory named
> 'click', so unless special measures are taken flit will end up importing
> the code it's trying to build.
>
> But of course this can happen for lots of reasons; most packages have
> names that you wouldn't expect to randomly encounter at the root of a
> source tree very often, but with 100,000+ packages on pypi I expect it will
> happen eventually.
>
> This doesn't happen with setuptools because setuptools traditionally has
> few or no dependencies, but obviously we're changing that; the whole idea
> here is that now your build system has full access to pypi.
>
>
>
> This is something to be discouraged anyways, because it creates a sort of
> broken situation (the same situation that setuptools itself had). The
> problem is that if you’re starting from only sdists, you have a circular
> dependency that cannot be broken. You can’t build click, because  click
> requires flit, but you can’t install flit, because flit requires click. The
> only way to fix this is to either have an already built wheel that you can
> use (which obviously was either built with a flit that didn’t require
> click, or a click that didn’t require flit, or it’s provenance can be
> traced back to that) or do some hacks that will hopefully resolve the
> situation good enough to get your first wheel built.
>
> Setuptools tried to depend on things, and it broke shit for a lot of
> people because of this. You basically can’t depend on anything as a build
> system that uses you as a build system. You can only depend on things that
> use other, different build systems in the entire dependency tree. Likely
> the best thing for build systems to do is either have no dependencies, or
> to have minimal dependencies that promise to only use setuptools (or
> another build tool, which one doesn’t matter, just as long as it has no
> dependencies) forever (and have setuptools or this other build tool promise
> to never take a dependency).
>
> Or vendorize their dependencies? To me it seems unrealistic for a build
> system to have no dependencies at all. Or perhaps this is exactly what you
> meant :)
>
>
> —
> Donald Stufft
>
>
>
>
>
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