Versioning unversioned packages

[Gavan Fantom <gavan%coolfactor.org@localhost>]

Hi folks,

Occasionally we have packages which are not derived from a specific 
release upstream. Sometimes because the last release was a long time ago 
and a newer, unreleased, version is needed to do anything useful, and 
sometimes because upstream simply hasn't ever made releases and just 
expects people to use the latest version from github.

But in pkgsrc we need a version number for every package. How do we 
derive this version number in the case of packages where the author has 
not supplied a version number, and we are just stating a revision in 
github or similar?

Do we:

* Make up a version number such as pkgname-0.0
  - In this case there is the potential that it will clash with a 
version released by upstream in the future.
  - This may be a bit easier when a previous version has been released, 
but we need something newer even than that. Perhaps then pkgname-1.2b 
and hope that the next official release will be pkgname-1.3.

* Use the date of the last checkin, such as pkgname-20160610
  - What do we then do if upstream makes a formal release? How will 
version comparisons be affected if we switch from this format to 
pkgname-1.0?

* Something else?