Ability to hide a module variant #714

Module variants let a single modulefile expose several flavors of a software (app/1.0 compiler=gcc, app/1.0 compiler=intel, app/1.0 +debug, ...). Variants and their available values are reported next to the module name in avail, spider and list output and offered by shell completion. Today, all variants declared with the variant modulefile command are reported this way: there is no way to declare a variant while keeping it out of sight.

Feedback gathered at the HPSF Conference 2026 showed that this is a need for sites making real use of variants:

• Some variants are internal to the modulefile logic (a knob used to tune the environment for a given machine partition, a build option kept for one specific project, a compatibility switch) and are not meant to be chosen by regular users. Showing them in avail output clutters the listing and raises questions.
• Some variants are experimental or restricted to a few users. The site wants them to remain selectable by people who know about them, but not advertised to everyone.
• The module hiding mechanism (module-hide) offers exactly this kind of control for modulefiles as a whole, with the ability to lift the hiding for given users or groups, or after a given date. Sites that structure their stack around variants rather than separate modulefiles lose that capability.

The need is for a way to flag a variant as hidden. A hidden variant should not be reported in avail, spider and list output nor proposed by shell completion unless the user explicitly asks for hidden content (as --all does for hidden modules), but should remain fully usable when explicitly specified on the command line. It would be consistent to offer the same kind of conditions as module-hide provides, so the hiding can be limited to or lifted for specific users or groups.

Hiding a specific value of a variant, rather than the whole variant, is a related need but is left out of the scope of this first feature.

This would let sites keep variant listings focused on what users are expected to pick, while keeping the flexibility variants provide for internal or restricted use.