bug#71332: guix gc delete order

[Nicolas Graves]

Hi Guix,

I feel the way `guix gc` choose its files to delete quite
inconvenient. For instance, when developping big programs locally, I
often find myself missing space, but when I will `guix gc -C30G`,
instead of the expected unused items (not present in any profile, just
built but discarded as the package I'm building is updated for
instance), I will instead loose most of the native-inputs that are
needed to build my `guix home` and `guix system`.

This make me stuck in an endless loop of removing / redownloading over
and over the same native-inputs, while my intention is first to remove
files that aren't these native-inputs.

I haven't delved into `guix gc` yet, how hard is that issue to solve? 

-- 
Best regards,
Nicolas Graves