I have an extension to eglot (the language server protocol client in GNU
ELPA) that relies on this feature
Could you tell us what that extension is/does?
It implements the "files extension to LSP". It basically allows the
client and the server to have separate file systems. For example, the
server can run inside a Docker container, or the source code can be on a
remote system accessed by Tramp.
The specification is here:
https://github.com/sourcegraph/language-server-protocol/blob/master/extension-files.md
And my unfinished implementation is here:
https://github.com/nemethf/eglot/blob/xfiles-v2/eglot-x.el