Re: OSX FSEvents file watching support

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 18 Jul 2019 08:14:33 -0700
> From: "Muir Manders" <muir@mnd.rs>
> Cc: emacs-devel@gnu.org
> 
> lsp-mode in particular needs to watch your entire source code project for file changes and then relay the file names that were created/modified/deleted fo the LSP server. This is to handle when files change outside the editor, like when changing branches. The LSP server registers file globs for the types of files it wants to receive notifications for, which is normally just the source code files and maybe some project metadata files (e.g. "**/*.go" to watch Go files). The LSP spec delegates file watching to the editor because file watching is hard, and in general there are fewer LSP clients (editors) than LSP servers.
> 
> The current (kqueue, at least) backends must open many file descriptors to watch a large directory tree. FSEvents however can do this task efficiently.

Beware: like I said earlier, I don't expect these facilities to be
scalable enough for watching large trees that get a lot of frequent
changes.  AFAIK, lsp-mode developers recommend to turn off file
notifications when there are a lot of them.