RFC: make package build reproducible

[bmwiedemann]

without this patch, spack-0.16.0/lib/spack/docs/_build/texinfo/Spack.texi
varied in

@deffn {Data} spack.config.config_defaults = @{'config': @{'build_jobs': 4, 'build_stage': '$tempdir/spack@w{-}stage', 'checksum': True, 'concretizer': 'original', 'connect_timeout': 10, 'debug': False, 'dirty': False, 'verify_ssl': True@}@}

that caused resulting Spack.info and spack.1 files to differ as well.

It would probably be more appropriate to drop the build_jobs
default value when generating the Spack.texi file
but this code was hard to locate.

This PR was done while working on reproducible builds for openSUSE.

[adamjstewart]

I don't think this change is something that we want, as it changes the default parallelism for all users on all systems.

[bmwiedemann]

Maybe you know how/where the Spack.texi file is generated, so we could strip this number out?

[adamjstewart]

It looks like this file is generated when you run:

$ cd spack-0.16.0/lib/spack/docs
$ make texinfo

I'm not familiar with OpenSUSE's Reproducible Builds effort, maybe you can give me more info on what its goal is. When you say "package build", do you mean installation of Spack, or the usage of Spack as a package manager to install other software? Building the documentation certainly isn't necessary for running Spack, so if you could remove that then that would be an easy way to resolve the unreproducible problem.

[bmwiedemann]

We 'build' the spack sources into an openSUSE rpm package.
I think, our users appreciate having documentation. And it is probably not hard to have reproducible docs, when you look at this 1-line-patch. Worst case, we could do post-processing of the output, though the result would be more brittle.

[adamjstewart]

Thanks for the explanation!

And it is probably not hard to have reproducible docs, when you look at this 1-line-patch.

This 1-line-patch completely breaks Spack's ability to adapt to different platforms. While my laptop has 4 cores, my supercomputer may have 64 or 128 cores, and I would like to take advantage of them when building software.

@becker33 @alalazo @scheibelp I recall some talk of removing this variable and instead relying on the config files to avoid config duplication. Another option would be to make this a hidden variable so it doesn't end up in the documentation. Thoughts on this?

[alalazo]

Closing as stale. Feel free to reopen if you want to continue the discussion on this.