-----Original Message-----
From: Steve Cohen [mailto:stevec...@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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