The File Provider API is very limited. In particular, it can't be used to implement file systems where the directory hierarchy is dynamic. It can't materialize directories on `chdir(1)`, for example.

The design was obviously tailored for providers that implement real disk files, like Dropbox and Apple's own iCloud Drive.

Btw, Apple also ships with an undocumented 9P implementation. It seems to be used for mounting the host filesystem in virtualized guests. It is unclear if it can be made to work over a normal (non-PCI) transport like TCP.

I found the api incredibly hard to use as someone who hasn't used swift or macOS API's before. Because of the way some of the code runs as a separate plugin from the main app, you can't really use traditional logging as a debug tool. There is also a lot of split state to be handled. You have to provide sync anchors and diffed tree updates to change the folder contents, which just aren't available with most backends.

I started on a program to mount a website resource directory on your computer using this api, but I gave up due to the restrictions of the api: https://github.com/mathiasgredal/Itslearning

Because your software was written against FUSE and you don't wanna spend time rewriting it to accommodate Apple users.