Hello Florian!

Here is my version of your diff in attachment. With this patch
'guix build test-repo' works for the main branch of test-repo-channel,
i.e. it seems to solve one problem (I'm sure that 'guix build guile@3.0.99-git'
works as well for the guile channel, but didn't check this explicitly).
The other problem ('guix build -S test-repo') remains.

Regards,
Nigko