Re: "git merge" merges too much!

From: Dmitry Potapov <dpotapov@gmail.com>
Date: Nov 30, 2009, 19:22 UTC
Message-ID: <20091130192212.GA23181@dpotapov.dyndns.org>
In-Reply-To: <m1NFAji-000kn2C@most.weird.com>

On Mon, Nov 30, 2009 at 01:12:31PM -0500, Greg A. Woods wrote:

> 
> The way "git merge" works does concern me somewhat though as I try to
> figure out how I might use "topic" branches to develop local features
> and then merge them onto each supported release branch.

The basic idea of using topic branches is development is done on separate branches are merged to the release branch only when they are ready to be released. These branches are based on the oldest branch in what they may be included. It means that fixes are normally based on the stable branch and new feature are based on the master branch, i.e. the branch that contains changes for the next new feature release. Not all branches got merged immediately into master. For instance, the git project has 'pu' (proposed updates) and 'next' branches. Only when a new feature proved itself to be useful and reliable, it is "graduated" to the master branch. Thus the master branch is rather stable and it is released on regular intervals (no need for a long stabilization period).

The key difference comparing to what you may got used is that branches are normally based on the oldest branch in what this feature may be included. Thus normally changes are not backported to old branches, because you can merge them directly.

Show 6 quoted lines

> > Yes, you must cherry-pick or use rebase (which is a more featureful
> > version of the pipeline you mentioned).
> 
> "git rebase" will not work for me unless it grows a "copy" option ,
> i.e. one which does not delete the original branch (i.e. avoids the
> "reset" phase of its operation).

There is no reset phase... It is just reassigning the head of branch to point to a different commit-id. If you want to copy a branch instead of rebasing the old one, you create a new branch (a new name) that points to the same commit as the branch that you want to copy, after that you rebase this new branch. You can do that like this:

$ git branch new-foo foo

$ git rebase --onto newbase oldbase new-foo

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> It likely wouldn't make sense to base this new "copy" feature directly
> on "git rebase" though, especially in light of all the warnings about
> how "git rebase" isn't friendly when applied to already published
> branches.  I think in theory this "copy" feature won't cause problems
> for already-published branches.

The "copy" does not have the problem of rebase, but it has a different problem: You have two series of commits instead of one. If you found a bug in one of those commits, you will have to patch each series separately. Also, git merge may produce additional conflicts... So, copying commits is not something that I would recommend to do often.

Dmitry