[Reproducible-builds] automated diffoscope for parallel build bugs

[Chris Lamb]

> I understand that building with parallel disabled takes much longer
> for many packages so I don't know if this is just a lack of resources

It's more that we have two builds and I think (?) we would prefer to do
different values of N > 1. So a different kind of resource problem.

> I think it would be good to run at least periodically as code changes
> to ensure that parallel building hasn't broken anything
[..]
> I think it should probably be run over the entire archive since
> debhelper 10 will presumably be widely deployed.

It wouldn't be too much work to run such an test yourself or to use
our infrastructure.

The problem is all about how you use the results; in the case where a
package differed between builds you would not know whether this was
due to the parallelism that was introduced or whether the package
is inherently non-deterministic.

> Building everything in pkg-gnome svn individually with and without
> parallel and then running diffoscope by hand to compare every binary
> package is not much fun.

Right, so make all the pkg-gnome packages build reproducibly without
paralellism enabled (which you should do anyway) and then simply
build with parallel enabled.

If the SHA of any .deb is different, then you ipso facto have
identified an issue. No diffoscope inspection required.


Regards,

-- 
      ,''`.
     : :'  :     Chris Lamb
     `. `'`      lamby at debian.org / chris-lamb.co.uk
       `-