Declaring channel dependencies in the operating-system configuration

["Elais Player" <elais@fastmail.com>]

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Hi Guix!

One thing that I've often found to be annoying was manually adding a
channels.scm file to systems, and I've come up with a solution that I'd like to
share.

For those interested in having their channels.scm be added as part of the system
generation process, just do the following.

Create an object representing a scheme file using the `scheme-file` procedure

(define %guix-channels
  (scheme-file
        "channels.scm"
        #~(cons* (channel
                        (name 'example)
                        (url "https://example.org/channel.git"))
                 %default-channels)))

Then add the file-like object to your system services using the
extra-special-file procedure. It symlinks a file from the store to
/etc/guix/channels.scm and makes the channels declared there available to all of
your systems users.

(operating-system
  ...
  (services
    (cons*
      (extra-special-file "/etc/guix/channels.scm"
                          %guix-channels)
      %base-services)))

I think this is a pretty neat solution for those of us who need to use custom
channels, but I was wondering if this is something that can be improved on and
added to the top level operating-system declaration.

Just like we can declare hosts for the operating system would it be a good idea
to declare (channels #~(cons* (channel ...))) too?

Would it make sense to add it as a configuration in guix-service-type?

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