Hi Attila,

Attila Lendvai <attila@lendvai.name> writes:

>> > channels are a step towards this, but they are not enough in their
>> > current form to successfully accommodate for such a setup. an obvious
>> > thing that is missing is a way to formally express inter-channel
>> > dependencies, including some form of versioning.
>> 
>> 
>> Do we not have this? The manual documents a mechanism for channel
>> dependencies in "(guix) Declaring Channel Dependencies".
>> 
>> I haven't used it, but it looks like the dependencies are declared as
>> channels, which can have the usual branch/commit specifications to tie
>> them to specific versions.
>
> good point, thanks!
>
> i looked briefly at the code just now. it's not trivial, and it seems to treat the guix channel specially (because i don't need to specify it as a dependency in my channel's .guix-channel file), and i'm not sure how it behaves when e.g. two channels depend on the same channel, but pick two different commits... or all the other convoluted situations.

The situation you describe where two channels pick different commits for
a channel dependency *cannot* be made to work, at least using Guile.  I
think what would currently happen is that either:

1) Guix refuses to build (unlikely);
2) Guix just chooses one commit that it then uses to build all dependent
channels, contrary to the requirements;
3) Guix does build each channel with the proper dependencies, but the
final Guix will have profile collisions.

Best,
-- 
Josselin Poiret