bug#53915: No way of replacing an input in modify-input syntax structure but keep all the outputs

["Ludovic Courtès" <ludo@gnu.org>]

Hi,

Liliana Marie Prikler <liliana.prikler@gmail.com> skribis:

> Am Dienstag, dem 08.03.2022 um 17:11 +0100 schrieb Ludovic Courtès:
>> [...]
>> With the patch below, we get more sensible behavior:
>> 
>> --8<---------------cut here---------------start------------->8---
>> scheme@(guile-user)> (modify-inputs (append $5 $4)
>>                        (replace "glib" xpdf))
>> $8 = (("glib" #<package xpdf@4.03 gnu/packages/pdf.scm:395
>> 7f9b1457c9a0>) ("pkg-config" #<package
>> pkg-config@0.29.2 gnu/packages/pkg-config.scm:36 7f9b13a30580>)
>> ("glib" #<package xpdf@4.03 gnu/packages/pdf.scm:395 7f9b1457c9a0>
>> "bin") ("gobject-introspection" #<package
>> gobject-introspection@1.66.1 gnu/packages/glib.scm:428
>> 7f9b12994e70>))
>> --8<---------------cut here---------------end--------------->8---
>> 
>> If that makes sense to you, I’ll go ahead with this change and adjust
>> documentation accordingly.
> Sounds better than my own suggestion, since it'll keep working the way
> it did even when labels are eventually dropped.

Pushed with tests in 00dfff84c66c5c6aa4853684419a92befe55d4b4.

> If more control is needed, we can always later extend it to support
> (replace ("label" "output") (package output)).  WDYT?

I’d rather not: the goal of ‘modify-inputs’ is to provide an interface
that works as if input labels didn’t exist, with an eye on removing them
entirely in the future:

  https://guix.gnu.org/en/blog/2021/the-big-change/

Regardless, we’ll have to keep an eye on all these corner cases and to
adjust the plan accordingly.

Thanks!

Ludo’.