bug#35379: Long lines in `guix` output are truncated at screen width

[rendaw <7e9wc56emjakcm@s.rendaw.me>]

On 4/23/19 10:13 PM, Ludovic Courtès wrote:
> Hi rendaw,
>
> rendaw <7e9wc56emjakcm@s.rendaw.me> skribis:
>
>> I get logs like:
>>
>> /gnu/store/6zkimxsfyn0gdc7p4ikxlrhilpnpblsi-grub-efi-2.02/sbin/grub-install:
>> error:
>> /gnu/store/6zkimxsfyn0gdc7p4ikxlrhilpnpblsi-grub-efi-2.02/lib/grub/i386-pc/modinfo.sh
>> doesn't exist. Please spe.
> Hmm weird.  Can you tell exactly how to reproduce this issue?
> I don’t see what could be truncating these lines.
>
> Thanks in advance,
> Ludo’.

I thought this was normal, but I tried reproducing it in a vm.

It appears that the truncation starts after qemu starts the image in

```

guix system disk-image my-config.scm -v 10

```

and the truncation continues thereafter.  I tested by doing:

```

(display (iota 200))

(display "\n")

(force-output)

(display (iota 200))

```

This prints before and after the qemu step of the build.  Before the
qemu process it looks like lines are wrapped properly.  After the qemu
process the lines are truncated.  And lines are truncated before+after
for subsequent builds until I reset the vm.

I can send the Vagrantfile and provisioning script + what I did manually
to do the build if you'd like.

The main issue is the build fails, I turn -v 10 on to see the verbose
logs, but then the logs I need (during/post qemu) are truncated so I'm
still not getting the important information.