From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludovic.courtes@inria.fr>
Subject: bug#38100: =?UTF-8?Q?=E2=80=98--with-input=E2=80=99?= causes
 unintended rebuilds
Date: Thu, 07 Nov 2019 13:35:15 +0100
Message-ID: <87eeyjsw3g.fsf@inria.fr>
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To: bug-Guix@gnu.org

Hello,

Consider this example:

--8<---------------cut here---------------start------------->8---
$ guix build glib -nd
/gnu/store/9zz9hvzaz06f40a4cbvhskb183x676w4-glib-2.60.6.drv
$ guix build glib --with-input=3Dinkscape=3Dlibreoffice -nd
/gnu/store/15f9jkpakmsaz8i2a0gy4kir1zyk29vi-glib-2.60.6.drv
$ guix describe
Generacio 114	Nov 02 2019 11:32:51	(nuna)
  guix ab1c063
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: ab1c063ab08e069fbe62919828fa634a2e222bbf
--8<---------------cut here---------------end--------------->8---

Since GLib does not depend on Inkscape, the =E2=80=98--with-input=E2=80=99 =
flag should
have no effect: we should get the same glib derivation.  However, we=E2=80=
=99re
not.

If we diff the =E2=80=98glibc-2.60.6-guile-builder=E2=80=99 files of each d=
erivation, we
see that the second one has a duplicate entry:

  (define %build-inputs
    `(=E2=80=A6
      ("python" . "/gnu/store/78w7y0lxar70j512iqw8x3nimzj10yga-python-3.7.4=
")
      ("python" . "/gnu/store/78w7y0lxar70j512iqw8x3nimzj10yga-python-3.7.4=
")
      =E2=80=A6))

whereas the first one doesn=E2=80=99t have this duplicate entry.  IOW, the =
two
derivations are functionally equivalent but are not bit-identical.

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 not=
 =E2=80=98eq?=E2=80=99.

To be continued=E2=80=A6

Ludo=E2=80=99.