Neovim with coc-rust-analyzer.

There’s also coc-rls.

Given this project has been around for many years, (looking at their releases), I wouldn’t say it’s “early” to modularize their code. It’s very common practice to abstract out / move commonly executed code into their own packages and modules to allow ease of reuse across the app. This way if an entire subpackage needs to be moved or deleted, all related code could be affected at once and code which references it, simply needs to be edited. Typically these places to edit are much easier to handle since most of “calling code” wouldn’t touch the modularized / abstracted code, only their callables.