I’m using Subclipse 1.6x plugin in Eclipse. Let me explain the scenario first:
Say I have the trunk of my project with revisions r1 to r100.
At revision r100 I created a branch and started committing say r101 to r105.
At this point, I thought I will bring in any changes from trunk so that my branch is updated.
But due to a merging mistake, I end up merging r80 from trunk to my branch and committed it as revision r106. So I revert my change in r106 in the branch and do another commit r107 to this branch.
During this time there has been commits say r108 and r 109 in the trunk.
Now after reverting my bad commit in r106, I correctly bring in all changes from trunk until r109 to my branch (by merging) so that my branch is up to date, and commits this to my branch as r110.
All is good. Now I decided I don’t need the branch so let me merge all changes in branch (r110) back to trunk. So after this merge all I should see is the changes I made in the branch (revisions r 101 and later in that branch) as my branch is up to date with trunk.
I do a Team -> Merge with From url as trunk and To url as my branch path. The From revision is the last merged revision in trunk (r109) and the To revision used is the latest in my branch (r110). I tried a Dry Run and also creating a Unified Diff file option in the Merge window. Both of them looks correct and the only updated files are those I changed in my branch.
Now I run the Merge and and the merge result is different from Dry Run. First it correctly merges files shown by Dry Run (which is what I expected). But it doesn’t stop there. It then tries something like this:
— Merging r80 through r110 (May be because of my wrong merge in the branch???)
and then does something like:
— Reverse-merging r110 through r80.
The end result was merging in all my changes exactly as the Dry Run result plus a lot updates/changes to other files (due to second Merging and reverse-merging I guess).
Any thoughts on why this might be happening and how to make the merge result correct/same as the Dry Run result? Even the Unified diff file created is correct.
Thanks for reading through the lengthy post.
Ok I figured this out or at least solved it for my case. The issue was because on my branch I wrongly merged r80 from trunk and committed as r106. Then I did Team > Revert > last commit to revert this merge-commit and checked this as a new commit r107.
There are 2 issues with this. First this is not the best way to revert a merge commit in SVN. Google for more details.
Second issue is when you merge these changes (in multiple commits) back to trunk, SVN will try to apply each commit one by one to the trunk. As I messed up r106 on branch by merging r80, SVN gets confused about the change because of conflicting ancestry for the files. In order to avoid this, and to tell SVN don’t worry about the ancestry but just merge the differences/changes in my branch to trunk, check the “Ignore ancestry” option in the Merge window. This took care of the problem for me.
Also as a side note, in SVN merge, the result of Dry Run is equivalent to running Diff between the files. But when you do the Merge, it will look into the ancestry of the file and brings in each commit one by one to do the Merge. Hence the results may not always be the same. There is more details on this in SVN documentation.
This is what I understood from my experience and am posting this here as answer as I didn’t get any other responses to my post. Please add any comments if I’m not fully correct.