Subject: Re: bug#43843: git-annex is not Reproducible

From: Ricardo Wurmus <[email-masked]>
Date: Mon, 12 Oct 2020 12:36:00 +0200

zimoun <[email-masked]> writes:

> On Sat, 10 Oct 2020 at 11:34, Ricardo Wurmus <[email-masked]> wrote:
>
>> > --8<---------------cut here---------------start------------->8---
>> > 67cb9fa2357026ee42ec5bb0923ec4dc4a43abe2 is the first bad commit
>> > commit 67cb9fa2357026ee42ec5bb0923ec4dc4a43abe2
>> > Author: Ricardo Wurmus <[email-masked]>
>> > Date:   Tue Jun 16 22:25:48 2020 +0200
>> >
>> >     build-system/haskell: Support parallel builds.
>> >
>> >     * guix/build-system/haskell.scm (haskell-build): Add keyword
>> >       PARALLEL-BUILD?
>> >     and pass it on to the builder.
>> >     * guix/build/haskell-build-system.scm (build): Accept keyword
>> >       PARALLEL-BUILD?
>> >     and pass the number of parallel jobs to GHC.
>> >
>> >  guix/build-system/haskell.scm       | 2 ++
>> >  guix/build/haskell-build-system.scm | 7 +++++--
>> >  2 files changed, 7 insertions(+), 2 deletions(-)
>> > bisect run success
>> > --8<---------------cut here---------------end--------------->8---
>>
>> Shall we revert it?  Previously the build system also supported parallel
>> builds, but didn’t seem to pass the right arguments to actually make it
>> happen.
>
> What do the Haskellers think about that?

Let me answer as an ex-Haskeller :)

> Does the parallel build save a lot of time and CPU?  If yes, maybe we
> could to provide a transformation for the expert, something like
> "haskell-build-system-with-parellel-build" which tweaks
> "PARALLEL-BUILD?", similarly to the recent "no tests".  WDYT?

We shouldn’t compromise reproducibility for parallel builds.  Ideally we
would figure out what exactly causes the differences and fix that
instead of disabling parallel builds, but if that turns out to be too
difficult I think we should just revert this until we have a good fix.

Perhaps something can be done by fixing the order of files somewhere.

-- 
Ricardo