I don't think they will ever move 'secret sauce' into open source, but infrastructural things like DBs and dev tooling seems to be going in that direction.
Apple, like everyone else, wants to commoditize their complements.
Woolvalley said “and now recently clangd“, which is a source code completion server which began its life at Google.
Clang did start its life with Apple.
> Apple chose to develop a new compiler front end from scratch, supporting C, Objective-C and C++. This "clang" project was open-sourced in July 2007.
EDIT: My bad, looks like FoundationDB wasn't fully open-source back then.
You can even check the comments on the HN thread [1] when they removed the downloads.