How to merge branch back to trunk in SVN with all commit history?

With Subversion 1.5 or later the merge is recorded on your local working copy in the svn:mergeinfo property. So this information is not lost.

You can see the merged revisions if you use svn log -g instead of the normal svn log.

Normal merges are performed as

svn merge -rREV1:REV2 svn://server/branch my_trunk_wc 

But if you use a branch it is sometimes more convenient to use a reintegration merge. In this case you should first merge all trunk changes to the branch using something like

svn merge svn://server/trunk my_branch_wc

(This merges everything that is not already merged)

And after you commit this change to the branch you can use

svn merge --reintegrate svn://server/branch my_trunk_wc

To move all changes over as a single commit. (After this operation you should remove the branch)

To create a merge of a branch and create a single commit for each commit in the branch you can use a script, I'm using the following:

#/bin/bash

BRANCH="http://your branch url"

for i in {1127..1138} # list of revisions
do
  REV=$i
  echo $REV $BRANCH
  echo merged $REV from $BRANCH > tmps.commit
  svn log -c $REV $BRANCH >> tmps.commit
  svn up
  svn merge -c $REV $BRANCH ./
  svn commit -F tmps.commit
  rm tmps.commit
done

This will check out each revision you specify for the specific branch and perform a commit on the current directory, thus preserving each single change with the corresponding message.