bug#55011: let user drop into REPL from installer

[Liliana Marie Prikler <liliana.prikler@gmail.com>]

Am Dienstag, dem 19.04.2022 um 01:23 +0200 schrieb raingloom:
> I tried installing Guix with the installer, mostly to give LUKS a try
> in a low effort way, but also to hopefully find some bugs. I
> succeeded in the latter so far. :)
> 
> I did a manual partitioning, with an encrypted BTRFS root and an ext4
> /boot. The layout was left over from a previous failed encrypted
> install with automatic partitioning.
> 
> Long story short I got an error related to mkfs.btrfs, this I think
> has already been reported, but Mumi's search is not great so I
> haven't verified that yet.
> 
> The important thing is that I'd like not to reboot or start the
> installation from scratch. Scheme has call/cc and continuable
> exceptions and whatever, so could we let users at least attempt to
> fix these errors manually?
> 
> At the very least it would let them gather more info for debugging.
As far as I'm aware you still have four open terminals after things go
wrong in the graphical installer.  I'm not sure how much of the
automatic process actually mirrors the manual – we could aim for 100%
surely – but let's say you encounter an issue during mkfs as above,
then it'd be nice if Guix could just catch that error, check where we
are according to the manual, print out the backtrace and a nice message
"You can attempt to fix this by switching to manual installation and
continuing from SECTION/SUBSECTION."  Perhaps add a "fix manually"
button that switches to VT3, as well as your typical "Redo
installation".

Cheers