ufl team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

On 10 May 2011 17:52, Anders Logg <logg@xxxxxxxxx> wrote:
> On Tue, May 10, 2011 at 03:49:18PM +0200, Martin Sandve Alnæs wrote:
>> On 3 May 2011 18:25, Johannes Ring <johannr@xxxxxxxxx> wrote:
>> > On Tue, May 3, 2011 at 3:52 PM, Anders Logg <logg@xxxxxxxxx> wrote:
>> >> It happens to me a lot. Johannes has tried to explain to me why it
>> >> happens a number of times but I still don't understand why.
>> >>
>> >> Maybe he can try to explain it again to you and then I might also
>> >> understand. :-)
>> >
>> > I think I just bring up the following instructions (which I think looks good):
>> >
>> >  http://wiki.squid-cache.org/BzrInstructions
>>
>> Thanks Johannes.
>>
>> Basically the problem is that bazaar numbers commits with contiguous
>> integers, and when Bob and Alice works locally they will get the same
>> commit ids for different commits. When you stand in branch Alice and
>> merge from branch Bob, the commit numbers of branch Alice are
>> conserved and a single new merge commit is recorded on top there. The
>> commit numbers from branch Bob are lost in the merge. Therefore, to
>> conserve the commit ids in the central branch, you have to merge from
>> your own branch into the server branch, not the other way around.
>> Otherwise we can never safely use the commit revisions from the
>> central branch, since they may change every time somebody merges the
>> 'wrong way'.
>>
>> This problem does not occur with hg or git, because they use a hash
>> value to identify a each commit.
>
> So if I'm Bob and Alice has pushed some changes to the main branch
> before me, which exact commands should I write?

Depends on how you set up your repositories, where your branches are
located, etc...

You really have to read up on it and try it out a bit to understand
it, and I doubt I can write it better than what Johannes linked to +
the bazaar docs.

I plan to keep a local repository with multiple branches like this:
  ~/dev/fenics/ufl/ - local ufl repository
  ~/dev/fenics/ufl/trunk/ - local checkout of central ufl branch lp:ufl
  ~/dev/fenics/ufl/work/ - local branch where I usually do my work
(  ~/dev/fenics/ufl/somefeature/ - local branch with some half
finished feature if needed)

One branch locally for normal work, one checkout locally mirroring the
central trunk, and any number of branches locally and on launchpad for
alternative half-finished work.

Then I do:

cd .../ufl/work/
<work work work>
bzr push lp:ufl # fails because Bob has pushed stuff
cd ../trunk # should have no local changes now
bzr update # gets the latest version of lp:ufl
bzr merge ../work # merge my work into trunk
bzr commit -m'Merge my work on <superfeature>.' # Commit merge into trunk

If trunk is a _checkout_ and not just a _branch_, the last commit here
will actually both commit and push the merge to lp:ufl directly.

To use bazaar correctly, everybody really needs to read up on it and
understand the differences beteween e.g. a checkout and branch.
Otherwise nobody can ever trust FEniCS revision numbers to mean
anything... I'm a bit surprised on this bazaar 'feature'.

Martin