Re: [BuildStream] Merging 'git_tag' and 'git'

[Thomas Coldrick <thomas coldrick codethink co uk>]

Hi Jürg,

I added the functionality for (3) to git_tag, so may be able to shed
some light as to what the use case is. This was added to automate some
of the tracking of new major versions for projects that use release
branches.

The workflow makes more sense when you want to always keep up to date
with the latest stable release, but also catch bug fixes on your
current minor version. For example, the master branch of freedesktop-sdk
would like to keep as up to date as possible but not miss tags on the
current release branch.

For an example, imagine the scenario where we track master and release/1.8.
If run `bst source track` and get a new tag of 1.9.0, we know that we must
switch our tracking branch to this now. I think the context that was missing
is that this is intended to alert to new major releases, not automatically
track to them.

Of course, this workflow is far from perfect, and maybe doing some more
interesting things like automatically detecting new release branches and
updating the tracking branch would be better, but at the time I couldn't
see a better way to solve the problem, and wasn't aware of your 
suggestion in
#220.

Thanks,

Tom