Ted Kremenek writes on the swift-dev list:

This afternoon at WWDC we announced a new refactoring feature in Xcode 9 that supports Swift, C, Objective-C, and C++. We also announced we will be open sourcing the key parts of the engine that support file-level transformations, as well as the compiler pieces for the new index-while-building feature in Xcode.

We will be releasing the sources in stages, likely over the next few weeks:

– For the refactoring support for Swift, there are some cleanups we’d like to do as well as some documentation we’d like to author before we push these sources back. Argyrios Kyrtzidis and his team from Apple will be handling that effort.

– For the refactoring support for C/C++/Objective-C, these are changes we’d like to work with the LLVM community to upstream to the LLVM project. These will likely be first staged to the swift-clang repository on GitHub, but that is not their intended final destination. Duncan Exon Smith and his team from Apple will be handling that effort.

– We’ll also be open sourcing the compiler support for indexing-while-building, which include changes to both Clang and Swift. Argyrios and his team will be driving that effort. For the clang changes they will likely be first staged to swift-clang, and then discussed with the LLVM community to upstream them to mainline Clang.

– Finally, we will be open sourcing the remaining pieces of the Swift migrator. Argyrios and his team will be handling the push back of changes there, and those changes will only be impacting the swift repository.

As usually, we’ll also be pushing back changes to have Swift work with the latest Apple SDKs. We’re expecting that push back to happen early next week. When that happens we will temporarily lock commit access to the repositories. Details about that will be sent out later in a later email. Until then, the downloadable toolchains from Swift.org will continue to work with Xcode 8.3.2. After we do the push back the downloadable toolchains will be moved to be baselined on the Xcode 9.0 betas. This shift is necessary as changes to the overlays depend on the latest SDKs.