We now have a swift-4.1-branch of Clang/LLVM, and it is time to update our “stable” branch to use that. This transition will merge in changes to the Swift master branch from the master-next branch that we maintain to work with upstream LLVM.
We are planning to make the change this Thursday, Aug. 3, around 2:00 pm (PDT).
When this happens, you will need to do a clean build of Clang/LLVM along with Swift. Do not just build the “clean” target — you should completely remove your entire build directory and then rebuild from scratch. There may be some instability after this transition as uncommon problems with the new version of LLVM are discovered.
I’ll send a reminder on Thursday. Let me know if you have any questions or concerns.