Interop with swift from a foreign language

With swift v5's "abi stability" on the horizon, is there any documentation/information available on how to do interop from foreign language to swift compiled libraries?

Background: I have my own compiler that can target osx, ios, linux, windows and for the targets where it makes sense I want to be able to interact with Swift objects (descend from them, call into them, etc).

There is partial documentation under the docs/ABI directory of the compiler source, but nothing really up-to-date or comprehensive yet.