Re: configurable guile backtrace in builder

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hello,

Ludovic Courtès <ludo@gnu.org> writes:

> 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.

Okay.

>> 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?

That sounds like a reasonable solution to me!  It's pretty "fixed" while
I would have preferred a user-configurable value, but it's better than
the current situation, so I'd say let's go for it on core-updates!

-- 
Thanks,
Maxim