bug#57307: guix system reports an error when uuid is used in menu-entry

[Josselin Poiret]

Hi, 

tiantian <typ22@foxmail.com> writes:

> I want to add an menu-entry in bootloader-configuration. I use uuid to 
> specify the partition in device field of menu-entry , because my 
> partition has no label. But when I use 'guix system reconfigure', guix 
> system reports an error: "guix system: error: #<<uuid> type: dce bv: 
> #vu8(109 91 19 212 96 146 70 208 139 228 7 61 192 116 19 204)>: invalid 
> G-expression input"

Right, this is an issue with how we translate the menu-entries to sexps
through `menu-entry->sexp`, which then get embedded into a g-exp via
`operating-system-boot-parameters-file`!  We didn't take into account
non-string devices there.  The following two patches should fix the
issue and introduce some tests for it.

Best,
-- 
Josselin Poiret