guix-jupyter's ";;guix pin" doesn't support channels.scm?

[Phil]

Hi all,

Reading:

https://gitlab.inria.fr/guix-hpc/guix-kernel/-/blob/68b525b241cf952940d4bf66e2697c2d1f3722e5/README.org


There is no explanation of how the ";;guix pin" command can pin multiple 
channels.

Looking at the source code it seems to only try to match the commit id against 
the contents of %default-channels:

https://gitlab.inria.fr/guix-hpc/guix-kernel/-/blob/341aecd8b4358b1b0a0c94235d7601f92c7b9942/guix-jupyter-kernel.scm#L551


My understanding is that %default-channels won't be augmented with any channels 
defined in /etc/guix/channels.scm or ~/.config/guix/channels.scm, which means 
it is impossible to pin any auxiliary channels beyond those defined as defaults.

I note if I run ";;guix describe" without ";;guix pin", all 3 channels are 
returned as per my /etc/guix/channels.scm - so by default it seems to take set 
itself using the channels.scm, but then only allows us to pin the main guix 
channel.


My question is how to I pin multiple channel definitions as part of my notebook?

Will running jupyter inside 'guix time-machine' with a channels.scm file
do this? The only problem I see with this is that we've created an
external file required to define how to run jupyter which breaks the
"everything defined inside the notebook" aim?

Cheers,
Phil.