I’m a long term Emacs user. When I first started writing rust I concocted an Emacs configuration using racer-mode and rust-mode directly which got the job done. Since then the state of Rust editor support has come a long way. I’ve finally taken the plunge and moved to RLS for a richer language completion experience.

RLS is the Rust Language Server. It implements the standardised “language server protocol”; which provides a common interface between editors and language completions. For Rust it uses a mixture of racer the Rust autocompletion tool and more heavyweight analysis.

Before setting things up you need to make sure you have a few toolchain components installed:

$ rustup component add rust-src rls-preview rust-analysis rustfmt-preview

The good news is that these should all be available on the stable toolchain right now.

Configuration wise I prefer to manage things with use-package. For a simple setup you should just need rust-mode and lsp-mode:

(use-package rust-mode
  :ensure t
  :mode "\\.rs"
  :init (add-hook 'rust-mode-hook 'lsp))
(use-package lsp-mode
  :ensure t
  :defer t
  :commands lsp
  :config
  (use-package lsp-clients))

Personally I prefer to use Company for completions. To switch to that all you ned to do is require the company-lsp mode.

(use-package company-lsp
  :ensure t
  :after company)

That should be it. I like to keep my mode line neat and tidy so my full configuration contains a few :diminishes and re-maps some keys. Check out the final result. My old racer-mode config is there too, commented out for posterity.