Generate spec file for RPM packages

[UebelAndre]

This is a feature request for pkg_rpm to have a similar set of attributes to pkg_deb such that the spec file can be generated within the rule. Having this would make it easier to maintain releases and enable users to define a single source of truth for package information without having to write a bunch of genrule magic.

[nacl]

We've been working on something like this for a while. See the rules in https://github.com/bazelbuild/rules_pkg/tree/main/pkg/experimental. They function more or less correctly, but the interfaces are not yet stable.

This task is ongoing; please feel free to chime in with any questions, comments, or ideas :)

See also #128, #129.

[UebelAndre]

That's perfect, thank! Any idea when the interface will stabilize?

[nacl]

We should have a better idea soon, but if I were to make a guess now, I'd say late this year or early next year.

FWIW, the experimental rules are very usable right now, but we've found some potential ways to refine them that can make specifying large packages much easier. We're going to be discussing them and hope to implement them soon. One such option is #238.