Create icommand irmdir

[rskarbez]

Functionality would be the same as Unix rmdir.

Requested in irods/irods#3117.

[trel]

please cherry-pick to 4-2-stable

[mcast]

Thanks for implementing it. I skimmed the code (possibly misunderstanding it in the process) and wondered, does it give the same safety guarantees as the POSIX equivalent?

1. check the collection is empty - yes.
2. equivalent to irm -r, wrapped as irmdir

This is fine until,

1. without getting an exclusive lock on the collection,
2. check the collection is empty - yes.
3. some other client sneaks in and writes a file
4. equivalent to irm -r, wrapped as irmdir
5. disappointment and data loss?

Could you make the safety guarantee, or lack of, explicit in the irmdir -h text please?

[rskarbez]

Thanks for checking this; I hadn't considered that potential case. I will certainly update the help text, and will look into what it would take to make the equivalent safety guarantees as the POSIX equivalent.