Dealing with Structural Conflicts
So far, we have only talked about conflicts at the level of file content. When you and your collaborators make overlapping changes within the same file, Subversion forces you to merge those changes before you can commit.
But what happens if your collaborators move or delete a file that you are still working on? Maybe there was a miscommunication, and one person thinks the file should be deleted, while another person still wants to commit changes to the file. Or maybe your collaborators did some refactoring, renaming files and moving around directories in the process. If you were still working on these files, those modifications may need to be applied to the files at their new location. Such conflicts manifest themselves at the directory tree structure level rather than at the file content level, and are known as tree conflicts.
Tree conflicts prior to Subversion 1.6
Prior to Subversion 1.6, tree conflicts could yield rather unexpected results. For example, if a file was locally modified, but had been renamed in the repository, running svn update would make Subversion carry out the following steps:
Check the file to be renamed for local modifications.
Delete the file at its old location, and if it had local modifications, keep an on-disk copy of the file at the old location. This on-disk copy now appears as an unversioned file in the working copy.
Add the file, as it exists in the repository, at its new location.
When this situation arises, there is the possibility that the user makes a commit without realizing that local modifications have been left in a now-unversioned file in the working copy, and have not reached the repository. This gets more and more likely (and tedious) if the number of files affected by this problem is large.
Since Subversion 1.6, this and other similar situations are flagged as conflicts in the working copy.
As with textual conflicts, tree conflicts prevent a commit from being made from the conflicted state, giving the user the opportunity to examine the state of the working copy for potential problems arising from the tree conflict, and resolving any such problems before committing.