The initial set of documentation pages that describe how to mix Swift and C++ has now been published on swift.org, following the announcement that Swift 5.9 will include support for C++ interoperability.
The main reference guide describes how to mix Swift and C++.
The status page describes the currently supported feature set and lists some limitations and constraints.
The build and project page describes how to setup a mixed Swift and C++ project in Swift Package Manager or Xcode, and also describes how to configure C++ interoperability in a custom build configuration.
We will add additional contents related to CMake project setup later this month. Note that a CMake sample that shows how to use bidirectional interoperability is already available on GitHub.
The @cxx-interop-workgroup is excited to hear your feedback! Please post any feedback you have here on the forums, or file an issue on GitHub.