OK, the results are in - I've found a workaround.
Due to our legacy build processes (build, copy, obfuscate, build custom installers, copy to drop folder), I can't easily place the branch alongside the main branch. It needs to replace it.
So, if I have Main and NewFeature, I wish to unmap Main and map NewFeature in its place (i.e. use "c:\Main" on the build server, and simply change the source code that appears there)
Solution #1 (the most simple, obvious and logical solution) is to use these mappings:
Expected result: NewFeature code structure simply replaces Main, and the build server doesn't know it's on a different branch.
Actual Result: Failure with a "you haven't mapped $/Main even though you're not using it" error.
Solution #2 is to do this:
- $/Main -> c:\IgnoreThisFolder
- $/NewFeature -> c:\Main
This works (it suppresses the warning and thus allows the build to proceed with MSBuild unaware that it is building in a branch). However, it's ugly and the build gets all the Main branch source code unnecessarily.
Solution #3 (untested, too expensive to try unless I know it'll work much better than #2) is:
- Move all the source code (from $/Main, $/Branches/Feature) to $/Branches/Main and $/Branches/Feature to get a consistent hierarchy depth, and rewrite the MSBuild script to work with these new paths.
Hope that I can then map in only the branch I need and edit TFSBuild.proj to redirect it to build in that branch.
(Edit: Yes, this works well. We have now reorganised our entire code structure so that everything (all branches) is under a common root in a single Team Project, and branching/building is no longer a problem - it's easy to do whatever we need now. The trick is to insert a root folder into the hierarchy so that you can branch at any level you like. I've added a small tweak to the build script so that we can pass the branch to build as a parameter to MSBuild, so it's easy to build any variant now. Any branches we don't want to work on can just be cloaked and the build server remains happy.)
Summary
All these solutions (to use the technical term) suck. You have to remap the workspace (in this case, it's not simple: 9 mapping entries are required so it's an error prone and tedious thing to do), edit the TFSBuild.proj, delete all the source code, and run a build with /p:ForceGet=true to switch the build between branches. So it takes about an hour to switch branches. Unbelievable - it should take a few minutes at most!
I realise our project is far from ideally set up, but I can't believe it should be this difficult to branch in TFS (It was a piece of cake in SourceSafe, Accurev, and Perforce, so why so painful in TFS?).
How does everyone else organise their TFS branches? How do you switch developers between branches? How do you switch server builds between branches? Does it really have to be this painful?