Re: Turning off tests leads to a different store item

[Saku Laesvuori <saku@laesvuori.fi>]

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On Wed, Nov 08, 2023 at 10:18:40AM -0800, Vagrant Cascadian wrote:
> On 2023-11-08, Felix Lechner via wrote:
> > On Wed, Nov 08 2023, Maxim Cournoyer wrote:
> >> A source tree doesn't produce a derivation.  A derivation is the
> >> complete build recipe that captures the source and the package
> >> definition, that when built by the daemon produces a store item.
> >
> > Okay, thanks! Now I'm going to get it right:
> >
> > The store item that is produced should not change whether build-time
> > tests run or not.
> >
> > It does not make sense (and wastes resources) to rebuild a consuming
> > package because build-time tests were enabled or disabled in an input.
> 
> I do not really think people are misunderstanding you, more that your
> *should* does not align with reality in a way that guix can depend on;
> build-time tests *do* affect the build result in some cases.
> 
> [...]
> 
> The only way to ensure they do not change the build results is even more
> resource-intensive; systematically run the build without tests and then
> run the build with tests and compare the store items... assuming the
> build is reproducible in the first place, which is not yet 100% reliable
> either, unfortunately.

There is another way: simply preventing the tests from changing the
resulting store item. For example, the package could first be built
without tests and then that build tree could be copied to the build tree
of the build with tests enabled. The result of that build could then
just be copied from the testless build, ignoring any changes the test
suite has made to the build tree. I'm not confident enough in my
understanding of how Guix builds things to say for sure that this
specific method would work, but I am quite sure that the general idea is
implementable.

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