Feature Request: allow pkg_filegroups to contain pkg_filegroups

[kwc]

Currently, pkg_filegroup rules can only be aggregated by a pkg_tar rule. I would like to be able to aggregate pkg_filegroup rules with another pkg_filegroup rule -- i.e., I would to specify pkg_filegroup rules as srcs to another pkg_filegroup.

Use case: Due to Bazel incompatible target skipping, we provide explicit targets in our CI testing. I would prefer to test our deployment build with a pkg_filegroup target, but I instead have to test with a pkg_tar target, which adds expensive disk I/O. I would test with multiple pkg_filegroup targets, but this means maintaining the aggregated lists in two places.

With rules_pkg 0.5.1 I get this error if I try to aggregate pkg_filegroup rules:

<target name> does not have mandatory providers: 'PackageFilesInfo' or 'PackageDirsInfo' or 'PackageSymlinkInfo'

[nacl]

This should already be addressed in main as of 8d54276. Please try it out and confirm whether it works for you.

[nacl]

Closing; duplicate of #415. Please comment if you do not believe this is the case.