[Modules] Ongoing work: module variants

[Xavier D. <xav...@gm...>]

Dear All,

It is time to unveil some details on the ongoing work: next version
(4.8) will be focused on the "variant" concept, aka the ability to
pass arguments to your modulefiles for their evaluation.

It will rely on the Spack syntax [1], already used on Modules advanced
version specifiers, as this syntax covers all needs and some of the
Modules user are already familiar with it.

For instance to load the MPI version of the HDF5 library built over
the foss21a toolchain, you will be able to write:

$ ml hdf5+mpi toolchain=foss21a

It will also be possible to define shortcut for variant, for instance
to abbreviate "toolchain=" by "%":

$ ml hdf5+mpi %foss21a

Regards,
Xavier

[1] https://spack.readthedocs.io/en/latest/basic_usage.html#variants