bug#25235: Wrapped python programs get native-inputs in PYTHONPATH

[Arun Isaac <arunisaac@systemreboot.net>]

> “Build-side” modules, which typically live in (guix build …), should not
> depend on “host-side” modules such as (guix packages).  That’s because
> if we did that, we’d effectively end up importing all of Guix on the
> build side, but then we’d also have to serialize data structures such as
> packages to pass them from one side to the other.  (I hope this makes
> sense to you, but if it doesn’t maybe the intro of
> <https://gnu.org/s/guix/manual/html_node/G_002dExpressions.html> can
> shed some light.)

It makes some sense, but I'll read up more.

> So in short, we cannot use ‘package-name’ and
> ‘package-transitive-target-inputs’ in this module.

Ok.

> (Time passes…)
>
> I wasn’t sure how to fix this bug myself so I gave it a try and ended up
> with the patch below, but I haven’t tested in detail.  (You’ll notice
> (guix build-system python) is hard to work with because it doesn’t use
> gexps yet.)
>
> How does it look?

I'm travelling now. I'll get back on Monday and study this patch.