[Nix-dev] parallel make

[Peter Simons]

Hi Michael,

 > I would sometimes [like to] try to build my system with maximum
 > parallel building enabled just to record what breaks this time.

yes, it would be great if that were possible.

As of today, the only way to enable parallel building for all packages
is to override the default for "enableParallelBuilding" in the generic
builder, but if you do that you'll end up with a different stdenv. That
is unsatisfactory.

If /etc/nix/nix.conf would offer an option to determine the default
value of "enableParallelBuilding", then we could have the best of both
worlds. By default, parallel building would be enabled only for those
packages that explicitly request it. For the purposes of testing and
development, however, one could flip the switch and have parallel
building enabled for all packages that don't explicitly disable it.

In other words, users would be able to switch between opt-in and
opt-out.

Best regards,
Peter