CKAN is stored in a mercurial repo and we have devised this process to cope with coding, releasing and maintaining versions of the software.
We have a number of maintained branches of the code to reflect their uses:
default branch is for future releases - New features go here. Bug fixes should always go here as well as the other branches.
metastable branch is for releases deployed to ckan.net and similar servers. These servers get new features first. Sometimes there are issues to be resolved with these new features. It usually lags default.
stable branch is for very stable code - major releases. It usually lags metastable.
ultrastable branch is for the most stable code - major releases, one behind stable.
(From now on) merges must only be done in the DOWN direction (in the direction default->metastable->stable->ultrastable) and only when you release. This means that you would release default to metastable with a merge, and from metastable to stable, but you must not merge metastable to default, for example. And not when you simply fix a bug.
The problem with merging in the other direction is that bugfix changesets on metastable may well be mixed in with changesets incrementing the minor digit of the version number. The version number on the default branch may already have a higher major version and you don't want to overwrite it with the metastable changeset. When you merge you can't pick and choose changesets - you have all up to a certain one - so you can't merge in this direction.
You might have written a bugfix in default that you want in metastable too, but don't want the rigmorole of releasing at this point. In this case, don't merge - the problem with merging when you're not releasing, is that you may well pull half-finished features from default into branches which need to be more stable.
The solution (instead of hg merge) is to hg export particular changesets from one branch and hg import it to another.
'tip' note
Mercurial tags the latest commit with the tag tip. This means it changes on every commit and might be on any branch. So it's best not to refer to it in documentation, emails or changeset comments.
Version numbers
We generally have a major and minor version number. e.g. 1.5 Note: it is not a decimal number, simply integers separated by a dot. 1.11 is 'one point eleven', not 'one point one one' and is a later release than 1.2.
On the default branch, when you approach a release, we up the minor version number, and add a to indicate alpha, e.g. 1.2a. There may be further trial states e.g. 1.2b and 1.2c, before the final release of 1.2.
The final release goes to the metastable and eventually the other branches too, keeping this version number.
Bugfixes may appear on branches, yet by default, the code will keep the same version number. If the fix is warranted enough to be released as a point release, then the version number on default is upped (e.g. to 1.2.1), and the change made on other branches that have the fix. Note, because default may have other changesets since the release unrelated to the fix, we can't merge from default to the branches for either the bugfix or the version number change - use hg import and hg export.
