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From "Feldhacker, Chris" <Feldhacker.Ch...@principal.com>
Subject RE: Understanding merging
Date Tue, 08 Mar 2011 22:27:28 GMT
 
-----Original Message-----
From: Steve Cohen [mailto:stevecoh1@comcast.net] 
Sent: Tuesday, March 08, 2011 12:20 PM
To: users@subversion.apache.org
Subject: Understanding merging

> I work with a very senior colleague who has never always resisted version control and
would much rather do without it, but he is forced to go along and I am the whipping boy whenever
something goes wrong.
> He poses a general but simple question that I find myself unable to give a simple answer
to.  I am rephrasing it slightly but it bothers me that I don't know the simple answer.  If
I found myself in this situation I would tweak until it was as desired, but my persnickety
colleague is not satisfied with such answers and for once, I don't blame him.
> Given two branches off a trunk that were taken at different times, if the first is merged
back to the trunk and then the second, how may the second be merged back into the trunk so
as not to override changes from the first merge, assuming that both change sets are desired
to be in the trunk at the end?



Do the branches receive updates from trunk or not?
If the answer is yes, then before merging a branch back to trunk, one final update from trunk
to the branch must be performed.  The branch is now up-to-date with trunk, and (ideally) the
changes on the branch should be retested to make sure everything works.  When ready, the branch
is merged using the "reintegrate" option back to the trunk.  Using "reintegrate", the differences
between the branch and the trunk are computed and the changes applied to the trunk.

If the answer is no, then when the changes on the branch are ready to be merged back to the
trunk the "reintegrate" option must NOT be used.  Without "reintegrate", the changes made
on the branch are collected and effectively "replayed" on the trunk, which will have the desired
result regardless of whether or not additional changes to trunk have already been made.

So, a specific decision must be made as to whether or not "reintegrate" should be used, and
the correct answer depends on whether or not the branch receives updates from trunk during
its life.  

As long as the correct choice is made each time a branch is merged, then no changes will be
undone or "overridden".

(It would be really nice if Subversion could detect that a branch has received updates from
the origin and follow the best practice of "do the right thing by default", but...it is what
it is!)






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