Ha as soon as he mentioned LSP I knew it was going to be about the insane fact that it sends all text as UTF-8 (and Rust uses UTF-8) but it uses UTF-16 code points for column indexes. (I assume that is what it is anyway; I did not make it to the end, sorry.)

They've had an open bug about it for years but I think most people just ignore the issue because to handle it correctly you have to convert to UTF-16 and back (again after VSCode has already done it) and it's just not really worth dealing with until Microsoft fixes their end.

Actually I just went back and double checked and Microsoft did actually fix it last year! You can now negotiate to get positions in Unicode code points instead. Rejoice!