From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Subject: bug#38100: =?UTF-8?Q?=E2=80=98--with-input=E2=80=99?= causes
 unintended rebuilds
Date: Fri, 08 Nov 2019 22:06:32 +0100
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References: <87eeyjsw3g.fsf@inria.fr>
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To: 38100@debbugs.gnu.org

Hi,

Ludovic Court=C3=A8s <ludovic.courtes@inria.fr> skribis:

> Indeed, evaluating:
>
>   (bag-transitive-inputs
>    (package->bag ((package-input-rewriting '()) glib)))
>
> shows that we have two =E2=80=9Cpython=E2=80=9D packages there that are n=
ot =E2=80=98eq?=E2=80=99.

The problem is that =E2=80=98glib=E2=80=99 depends on =E2=80=98python-libxm=
l2=E2=80=99, which uses
=E2=80=98python-build-system=E2=80=99 and thus has =E2=80=98python=E2=80=99=
 as an implicit input.

=E2=80=98package-input-rewriting=E2=80=99 doesn=E2=80=99t touch implicit in=
puts so it leaves
that implicit =E2=80=98python=E2=80=99 untouched.

Since =E2=80=98transitive-inputs=E2=80=99 (used by =E2=80=98bag-transitive-=
inputs=E2=80=99) uses pointer
equality, we end up with two =E2=80=9Cpython=E2=80=9D packages that are not=
 =E2=80=98eq?=E2=80=99 but
are functionally equivalent: the one produced by
=E2=80=98package-input-rewriting=E2=80=99, and the implicit dependency of
=E2=80=98python-libxml2=E2=80=99.  QED.

(This is essentially the same as <https://bugs.gnu.org/30155>.)

I=E2=80=99m not sure how to address it.

Ludo=E2=80=99.