Re: version numbers in ELPA

[Stefan Monnier]

> As I'm preparing another release of rt-liberation for ELPA I noticed
> that in my code I have:
>
> ;; Version: 2.01
>
> ...but ELPA displays it, and makes the directories under
> ~/.emacs.d/elpa, as "2.1".

Yes, version numbers are defined in ELPA (notice: not "GNU ELPA" but
"ELPA") as sequences of numbers.  Since 1 and 01 are one and the same
number, then ... 2.01 is the same as 2.1.

> Are there some implicit rules to follow as to how we should number
> versions going to ELPA? Are there some explicit rules I just skimmed
> over and didn't take note of?

Yes, the version numbers need to obey `version-to-list` and the actual
string used to represent the version number in the name of the tarball
need to be "canonicalized" by passing them to `version-to-list` and then
recreating a corresponding string out of it with `package-version-join`
(defined in `package.el`).  This need is because the `archive-contents`
file (which lists the tarballs available in a given ELPA server) give
the versions in the form of a list of numbers rather than a string, and
then `package.el` needs to "guess" the name of the corresponding tarball
by creating a string out of it.


        Stefan