OSX FSEvents file watching support

[Muir Manders]

Hello

I am interested in adding support in Emacs for Mac OS "FSEvents" file watching. FSEvents allows for efficient recursive directory watching, which would be a boon for packages like lsp-mode.

I seem to have three options:

1. Write a new backend for filenotify.el. The existing backends explicitly don't support recursive watching, so I'm not sure if it makes sense to have one special backend that does support recursive watching.

2. Publish a dynamic module that wraps the FSEvents API. It seems like most OSX distributions of Emacs have module support enabled, but I'm afraid there might be other challenges with this approach I don't know yet.

3. Publish an elisp package that calls out to an existing program that supports FSEvents like "fswatch". This approach probably has the least friction, but doesn't allow for tweaking FSEvents settings, and might have performance disadvantages.

Does anyone have any guidance on which approach makes the most sense, and in particular if a new recursive filenotify.el backend would be acceptable?

Thanks,

Muir