Re: configurable guile backtrace in builder

["Ludovic Courtès" <ludo@gnu.org>]

Hi Maxim,

Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:

> Ludovic Courtès <ludo@gnu.org> writes:

[...]

>> 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.

It’s not that it’s risky, it’s something we should never do; it’s crucial.

> 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?

How about passing #:env-vars '(("COLUMNS" . "200")) to
‘gexp->derivation’ (in the build system), or adding a phase that sets
that environment variable?

HTH,
Ludo’.