Development Workflow for Trac

We don't have very formal rules, so consider the following as some advice taken from our current practices.

Aim

The public branches (listed in TracDownload#LatestDevelopmentSourceCode) should ideally remain bug free and always usable from an end-user perspective, as we support people installing directly from there.

Initial code review

Except for trivial fixes, it's usually a good idea to start with a patch or an experimental branch, in order to provide some visibility of the changes to the other contributors.

The patch is generally attached to a ticket. When it appears that there are many iterations or spin-off changes needed, it's a good idea to start a branch, either in the svn sandbox for those who have the commit permission or inside an external DVCS repository, by forking our Mercurial or Git mirrors (see TracRepositories).

Integration in release branches

The general idea is that we commit bug fixes first on one of the stable branch (e.g. branches/0.12-stable​), then merge the fix to latter branches using svn's mergeinfo support.

Merging in this direction (porting or forward porting) makes it quite easy to merge all pending changes from one stable branch to the next, e.g. 0.12-stable​ to 1.0-stable​, then to trunk​. This workflow is much simpler than the opposite one, back porting, which involves cherry-picking or careful "blocking" of changes which shouldn't be merged back. The SCM tools have generally better support for merging in this forward direction, even Subversion since version 1.5 ;-)

Here's a walk through example. We start by hacking on 0.12-stable​:

0.12-stable$ ed trac/attachment.py # or your other favorite editor ;-)
0.12-stable$ make test
...
(all is good)
0.12-stable$ svn ci -m "0.12.6dev: fixed ... (#xyz)"

Now we want to port all the pending changes to branches/1.0-stable​:

0.12-stable$ cd ../1.0-stable
1.0-stable$ svn merge ^/branches/0.12-stable
1.0-stable$ make test
...
xxx
1.0-stable$ # some fixes needed for API changes
1.0-stable$ svn ci -m "1.0.2dev: Merged from 0.12-stable."

Now we want to port all the pending changes to trunk​:

1.0-stable$ cd ../trunk
trunk$ svn merge ^/branches/1.0-stable
trunk$ make test
...
xxx
trunk$ # some fixes needed for API changes
trunk$ svn ci -m "1.1.2dev: Merged from 1.0-stable."

Among the possible porting related fixes that should be done when porting:

• use Python idioms adapted to the minimal version on the branch (e.g. for 0.12 the baseline is Python 2.4, for 1.0 and trunk it's 2.5; this means that among other things we can use with ... as appropriate)
• use newer APIs and conventions (e.g. the DatabaseApi#Trac0.13API); see the ApiChanges subpage for the corresponding target branch

Note: one can always review what are the pending changes in Trac by looking at the svn:mergeinfo property which shows the eligible set of changesets, when viewing the target branch in the TracBrowser (e.g. trunk​)