configurable guile backtrace in builder (was: services: base: Add extra-env support to guix-configuration)

[Maxim Cournoyer]

+CC guix-devel

Hello!

Ludovic Courtès <ludo@gnu.org> writes:

> Hi!
>
> Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:
>
>> Side topic: I wonder if (with some changes to the daemon -- perhaps in
>> DerivationGoal::startBuilder) in nix/libstore/build.cc we could leak the
>> COLUMNS variable to be able to control the Guile builder backtrace
>> width.
>
> As a rule of thumb, I think we should keep the build environment
> unchanged forever—no changes to the set of environment variables and
> files/directories present in the build environment.
>
> It’s important because the whole reproducibile-by-construction approach
> depends on that.

I understand it can be risky to change anything on the builder side for
reproducibility.  Would you have an idea of the angle this problem
should be approached from, where the goal is to have a configurable
Guile backtrace width in the builder?

-- 
Thanks,
Maxim