Subject: [bug#43578] [PATCH 0/4] Rewriting implicit inputs with 'package-input-rewriting' & co.

From: Ludovic Courtès <[email-masked]>
Date: Wed, 23 Sep 2020 22:51:21 +0200

Hi!

zimoun <[email-masked]> skribis:

> On Wed, 23 Sep 2020 at 18:23, Ludovic Courtès <[email-masked]> wrote:
>
>> Concretely, the following commands had no effect thus far:
>>
>>   guix build python-itsdangerous --with-input=python=python2
>>   guix build hello --with-input=gcc=gcc-toolchain@10
>>
>> In both cases, this is because the input we want to change is
>> an implicit input.  This patch set fixes that, and it fixes
>> <https://issues.guix.gnu.org/42156> as a side effect.
>
> Awesome!
>
> Therefore, 'package-with-explicit-python' & co. are becoming obsolete
> (or almost), right?

Good question, we’d have to check on a case-by-case basis.
‘package-input-rewriting’ is coarser-grain: it can potentially rewrite
‘python’ dependencies deeper in the graph than
‘package-with-explicit-python’.

>> This opens new possibilities.  ‘--with-input=python=python2’ is one
>> of them, but ‘--with-input=gcc=gcc-toolchain@10’ is not (it fails
>> to build for obscure reasons that I’ll fix in ‘core-updates’, and
>> it rebuilds the world anyway, which is not practical).  Another
>
> Rebuilding the world, maybe. :-)  It is interesting in the HPC context
> where one would like use an "optimized" compiler, isn't?

Like I wrote, ‘--with-input=gcc=gcc-toolchain@10’ (or similar) isn’t
practical: you’d have to rebuild the world.

What I envision for the use case where you want to build a specific
package set with a different toolchain is to have a
‘--with-toolchain=PACKAGE=TOOLCHAIN’ option.  That would rebuild PACKAGE
with TOOLCHAIN.  Then it would either rebuild all its dependents (as per
‘--with-input’) or graft the rebuilt package (as per ‘--with-graft’).
The latter may not always be a viable option though, so I don’t know.

In fact I think it would be nice if the graft vs. rebuild choice could
be made independently for all the transformation options.

> Thank you.  I will give it a try for my use cases. :-)

Awesome, let me know how it goes!

Thank you,
Ludo’.