(I just lost a day or so tracking this down, so I hope this helps.)
bitflags 1.0.5 release crashes the Rust Language Server 1.34.0. In our case, peoples’ editors mysteriously stopped working after adding a new dependency (which happened to be
clap, but that was a red herring). The root cause was picking up 1.0.5 indirectly. The package has now been yanked, so if you
cargo update now it should revert to 1.0.4, fixing the problem.
To find the actual bug report against RLS, you have to already know that
bitflags was the problem, so here is a link for your convenience.