Figure 4.56. The Merge Wizard - Select Revision Range

In the From: field enter the full folder URL of the branch or tag containing the changes you want to port into your working copy. You may also click ... to browse the repository and find the desired branch. If you have merged from this branch before, then just use the drop down list which shows a history of previously used URLs.

If you are merging from a renamed or deleted branch then you will have to go back to a revision where that branch still existed. In this case you will also need to specify that revision as a peg revision in the range of revisions being merged (see below), otherwise the merge will fail when it can't find that path at HEAD.

In the Revision range to merge field enter the list of revisions you want to merge. This can be a single revision, a list of specific revisions separated by commas, or a range of revisions separated by a dash, or any combination of these.

If you need to specify a peg revision for the merge, add the peg revision at the end of the revisions, e.g. 5-7,10@3. In the above example, the revisions 5,6,7 and 10 would be merged, with 3 being the peg revision.

The easiest way to select the range of revisions you need is to click on Show Log, as this will list recent changes with their log comments. If you want to merge the changes from a single revision, just select that revision. If you want to merge changes from several revisions, then select that range (using the usual Shift-modifier). Click on OK and the list of revision numbers to merge will be filled in for you.

If you want to merge changes back out of your working copy, to revert a change which has already been committed, select the revisions to revert and make sure the Reverse merge box is checked.

If you have already merged some changes from this branch, hopefully you will have made a note of the last revision merged in the log message when you committed the change. In that case, you can use Show Log for the Working Copy to trace that log message. Remembering that we are thinking of revisions as changesets, you should Use the revision after the end point of the last merge as the start point for this merge. For example, if you have merged revisions 37 to 39 last time, then the start point for this merge should be revision 40.

If you are using the merge tracking features of Subversion, you do not need to remember which revisions have already been merged - Subversion will record that for you. If you leave the revision range blank, all revisions which have not yet been merged will be included. Read the section called “Merge Tracking” to find out more.

When merge tracking is used, the log dialog will show previously merged revisions, and revisions pre-dating the common ancestor point, i.e. before the branch was copied, as greyed out. The Hide non-mergeable revisions checkbox allows you to filter out these revisions completely so you see only the revisions which can be merged.

If other people may be committing changes then be careful about using the HEAD revision. It may not refer to the revision you think it does if someone else made a commit after your last update.

If you leave the range of revisions empty or have the radio button all revisions checked, then Subversion merges all not-yet merged revisions. This is known as a reintegrate or automatic merge.

There are some conditions which apply to a reintegrate merge. Firstly, the server must support merge tracking. The working copy must be of depth infinite (no sparse checkouts), and it must not have any local modifications, switched items or items that have been updated to revisions other than HEAD. All changes to trunk made during branch development must have been merged across to the branch (or marked as having been merged). The range of revisions to merge will be calculated automatically.

Click Next and go to the section called “Merge Options”.

Figure 4.57. The Merge Wizard - Tree Merge

If you are using this method to merge a feature branch back to trunk, you need to start the merge wizard from within a working copy of trunk.

In the From: field enter the full folder URL of the trunk. This may sound wrong, but remember that the trunk is the start point to which you want to add the branch changes. You may also click ... to browse the repository.

In the To: field enter the full folder URL of the feature branch.

In both the From Revision field and the To Revision field, enter the last revision number at which the two trees were synchronized. If you are sure no-one else is making commits you can use the HEAD revision in both cases. If there is a chance that someone else may have made a commit since that synchronization, use the specific revision number to avoid losing more recent commits.

You can also use Show Log to select the revision.

This page of the wizard lets you specify advanced options, before starting the merge process. Most of the time you can just use the default settings.

You can specify the depth to use for the merge, i.e. how far down into your working copy the merge should go. The depth terms used are described in the section called “Checkout Depth”. The default depth is Working copy, which uses the existing depth setting, and is almost always what you want.

Most of the time you want merge to take account of the file's history, so that changes relative to a common ancestor are merged. Sometimes you may need to merge files which are perhaps related, but not in your repository. For example you may have imported versions 1 and 2 of a third party library into two separate directories. Although they are logically related, Subversion has no knowledge of this because it only sees the tarballs you imported. If you attempt to merge the difference between these two trees you would see a complete removal followed by a complete add. To make Subversion use only path-based differences rather than history-based differences, check the Ignore ancestry box. Read more about this topic in the Subversion book, Noticing or Ignoring Ancestry .

You can specify the way that line ending and whitespace changes are handled. These options are described in the section called “Line-end and Whitespace Options”. The default behaviour is to treat all whitespace and line-end differences as real changes to be merged.

The checkbox marked Force the merge is used to avoid a tree conflict where an incoming delete affects a file that is either modified locally or not versioned at all. If the file is deleted then there is no way to recover it, which is why that option is not checked by default.

The checkbox marked Allow mixed revisions (not recommended) is used to allow merging into mixed-revision working copies (corresponding to the command line option --allow-mixed-revisions). The default since Subversion 1.7 is to disallow merging into mixed-revision working copies. The reasons are described in the Subversion book towards the end of the section Keeping a Branch in Sync . If you understand the possible problems of merging into a mixed-revision working copy you may select this checkbox to perform the merge anyway.

If you are using merge tracking and you want to mark a revision as having been merged, without actually doing the merge here, check the Only record the merge checkbox. There are two possible reasons you might want to do this. It may be that the merge is too complicated for the merge algorithms, so you code the changes by hand, then mark the change as merged so that the merge tracking algorithm is aware of it. Or you might want to prevent a particular revision from being merged. Marking it as already merged will prevent the merge occurring with merge-tracking-aware clients.

Now everything is set up, all you have to do is click on the Merge button. If you want to preview the results Test Merge simulates the merge operation, but does not modify the working copy at all. It shows you a list of the files that will be changed by a real merge, and notes files where conflicts may occur. Because merge tracking makes the merge process a lot more complicated, there is no guaranteed way to find out in advance whether the merge will complete without conflicts, so files marked as conflicted in a test merge may in fact merge without any problem.

The merge progress dialog shows each stage of the merge, with the revision ranges involved. This may indicate one more revision than you were expecting. For example if you asked to merge revision 123 the progress dialog will report “ Merging revisions 122 through 123 ”. To understand this you need to remember that Merge is closely related to Diff. The merge process works by generating a list of differences between two points in the repository, and applying those differences to your working copy. The progress dialog is simply showing the start and end points for the diff.

The merge is now complete. It's a good idea to have a look at the merge and see if it's as expected. Merging is usually quite complicated. Conflicts often arise if the branch has drifted far from the trunk.

For Subversion clients and servers prior to 1.5, no merge information is stored and merged revisions have to be tracked manually. When you have tested the changes and come to commit this revision, your commit log message should always include the revision numbers which have been ported in the merge. If you want to apply another merge at a later time you will need to know what you have already merged, as you do not want to port a change more than once. For more information about this, refer to Best Practices for Merging in the Subversion book.

If your server and all clients are running Subversion 1.5 or higher, the merge tracking facility will record the revisions merged and avoid a revision being merged more than once. This makes your life much simpler as you can simply merge the entire revision range each time and know that only new revisions will actually be merged.

Branch management is important. If you want to keep this branch up to date with the trunk, you should be sure to merge often so that the branch and trunk do not drift too far apart. Of course, you should still avoid repeated merging of changes, as explained above.

Subversion 1.5 introduced facilities for merge tracking. When you merge changes from one tree into another, the revision numbers merged are stored and this information can be used for several different purposes.

Merge tracking information is stored in the svn:mergeinfo property by the client when it performs a merge. When the merge is committed the server stores that information in a database, and when you request merge, log or blame information, the server can respond appropriately. For the system to work properly you must ensure that the server, the repository and all clients are upgraded. Earlier clients will not store the svn:mergeinfo property and earlier servers will not provide the information requested by new clients.

Find out more about merge tracking from Subversion's Merge tracking documentation .

Merging does not always go smoothly. Sometimes there is a conflict. TortoiseSVN helps you through this process by showing the merge conflict dialog.

Figure 4.58. The Merge Conflict Dialog

It is likely that some of the changes will have merged smoothly, while other local changes conflict with changes already committed to the repository. All changes which can be merged are merged. The Merge Conflict dialog gives you different ways of handling the lines which are in conflict.

For normal conflicts that happen due to changes in the file content or its properties, the dialog shows buttons which allow you to chose which of the conflicting parts to keep or reject.

If there's a tree conflict, please first see the section called “Tree Conflicts” about the various types of tree conflicts and how and why they can happen.

To resolve tree conflicts after a merge, a dialog is shown with various options on how to resolve the conflict:

Figure 4.59. The Merge Tree Conflict Dialog

Since there are various possible tree conflict situations, the dialog will show buttons to resolve those depending on the specific conflict. The button texts and labels explain what the option to resolve the conflict does. If you're not sure, either cancel the dialog or use the Postpone button to resolve the conflict later.

When you develop a new feature on a separate branch it is a good idea to work out a policy for re-integration when the feature is complete. If other work is going on in trunk at the same time you may find that the differences become significant over time, and merging back becomes a nightmare.

If the feature is relatively simple and development will not take long then you can adopt a simple approach, which is to keep the branch entirely separate until the feature is complete, then merge the branch changes back into trunk. In the merge wizard this would be a simple Merge a range of revisions, with the revision range being the revision span of the branch.

If the feature is going to take longer and you need to account for changes in trunk, then you need to keep the branch synchronised. This simply means that periodically you merge trunk changes into the branch, so that the branch contains all the trunk changes plus the new feature. The synchronisation process uses Merge a range of revisions. When the feature is complete then you can merge it back to trunk using either Reintegrate a branch or Merge two different trees.

Another (fast) way to merge all changes from trunk to the feature branch is to use the TortoiseSVN → Merge all... from the extended context menu (hold down the Shift key while you right click on the file).

Figure 4.60. The Merge-All Dialog

This dialog is very easy. All you have to do is set the options for the merge, as described in the section called “Merge Options”. The rest is done by TortoiseSVN automatically using merge tracking.