[bug#47989] [PATCH] channels: Add a #:system argument to channel-instances->manifest.

["Ludovic Courtès" <ludo@gnu.org>]

Hi Christopher,

Christopher Baines <mail@cbaines.net> skribis:

> Ludovic Courtès <ludo@gnu.org> writes:
>
>> Christopher Baines <mail@cbaines.net> skribis:
>>
>>> This allows computing a manifest for a specific system. Previously this was
>>> possible, but only through changing %current-system, which caused the
>>> derivation to be computed using that system as well (so computing a derivation
>>> for aarch64-linux on x86_64-linux would require running aarch64-linux code).
>>
>> I remember discussing it, but I wonder if I was confused.
>>
>> I think you can always do the equivalent of (say):
>>
>>   guix time-machine -- build -s armhf-linux hello -d
>>
>> … where Guix itself is built natively but it then computes a derivation
>> for a different architecture.
>>
>> The equivalent code would be roughly:
>>
>>   (let ((inferior (inferior-for-channels …)))
>>     (inferior-package-derivation store
>>                                  (car (lookup-inferior-packages inferior "hello"))
>>                                  "armhf-linux"))
>>
>> Does that make sense?
>
> Not really,

:-)

> this is just about manifests for channel instances, so nothing to do
> with package derivations as far as I'm aware.

I re-read your message and must have misunderstood.  It’s the derivation
of channel instances that you want for a given system, right?  (What’s
the use case though?)  In that case something along the lines of the
patch makes perfect sense.

Thanks,
Ludo’.