bug#43890: ‘package-input-rewriting/spec’ can introduce unnecessary variants

["Ludovic Courtès" <ludo@gnu.org>]

Ludovic Courtès <ludovic.courtes@inria.fr> skribis:

> Consider this example:
>
> $ guix describe
> Generacio 162	Oct 01 2020 00:23:38	(nuna)
>   guix 7607ace
>     repository URL: https://git.savannah.gnu.org/git/guix.git
>     branch: master
>     commit: 7607ace5091aea0157ba5c8a508129cc5fc4f931
> $ guix build inkscape --no-grafts -d
> /gnu/store/arjs5hb4wmy6dh5d3y8bbs808ki9abf8-inkscape-1.0.1.drv
> $ guix build inkscape --no-grafts -d --with-graft=glib=glib-networking
> /gnu/store/zd8mm3w6x9c97anfaly77fz28s5y3i5h-inkscape-1.0.1.drv
> $ guix build inkscape --no-grafts -d --with-graft=libreoffice=abiword
> /gnu/store/arjs5hb4wmy6dh5d3y8bbs808ki9abf8-inkscape-1.0.1.drv
>
> The last one is fine: it has no effect.
>
> The second one is problematic: since we’re using ‘--no-grafts’, the
> ‘--with-graft’ option should have absolutely no effect; yet, it yields a
> different derivation.

Fixed in 8db4ebb0cd9bfdcf1aea63eb8d20eb6af0c87c93.  \o/

It makes ‘--with-debug-info’ more practical.

The difficulty is to find out where the difference is and what piece of
code introduced a non-eq?-but-equal package.  Likewise, the test suite
catches corner cases that can take a while to address.

Related to that, commit 6b4663363c061071c10209f71aed1017a241af6c deletes
duplicates in ‘bag->derivation’, which should make the whole thing less
sensitive to the introduction of non-eq?-but-equal packages in the
graph.

Ludo’.