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

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

Re: configurable guile backtrace in builder

[Ludovic Courtès]

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’.

Re: configurable guile backtrace in builder

[Maxim Cournoyer]

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

Re: configurable guile backtrace in builder

[Attila Lendvai]

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


i assume printed guile backtraces should not be part of the normal output of any package.

and then why not introduce an env variable (or some other way) that only affects the backtrace, and nothing else?

-- 
• attila lendvai
• PGP: 963F 5D5F 45C7 DFCD 0A39
--
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