Fancy Rust development with Emacs

Rustup beta was released this week. As a member of the Church of Emacs I needed to update my config a bit. This inspired me to write this post on how to setup your Emacs as a great Rust IDE.

Installing Rust

Thanks to rustup installing Rust on your system is now even easier. First do:

λ curl https://sh.rustup.rs -sSf | sh

When prompted choose 1) Proceed with installation (default) unless you have some special requirements.

rustup was previously named multirust . It will create a ~/.multirust directory to store rust toolchains.

The binaries and tools will be installed in ~/.cargo . Make sure that you have ~/.cargo/bin in your PATH otherwise add it with:

export PATH = " $HOME /.cargo/bin: $PATH "

By default your projects will use the stable toolchain (Rust 1.8 at the time of this writing).

rustup has a lot of functionalities which you can find more about on the github page.

Crates and packages you’ll need

For this part I assume you already have a working emacs and that you know how to install packages and organize your configuration.

rust-mode

rust-mode handles syntax highlighting, indentation and various settings for you.

Just M-x package-install rust-mode .

cargo.el

Cargo is Rust package manager. cargo.el is a minor mode which allows us to run cargo commands from emacs like:

C-c C-c C-b to run cargo build

to run C-c C-c C-r to run cargo run

to run C-c C-c C-t to run cargo test

and many others.

As for installation, nothing fancy just M-x package-install cargo and add:

( add-hook 'rust-mode-hook 'cargo-minor-mode )

rustfmt

rustfmt formats your code according to community style guidelines just like gofmt in the Go language world. It’s automatically handled by rust-mode.

First install the rustfmt crate:

λ cargo install rustfmt

I use C-c <tab> a lot in my emacs to automatically indent the current buffer so it would be nice if the same key combination would run rustfmt which also fixes indentation. So I simply added:

( add-hook 'rust-mode-hook ( lambda () ( local-set-key ( kbd "C-c <tab>" ) #' rust-format-buffer )))

The ìndent-buffer function I mentioned if you ever need it:

( defun indent-buffer () "Indent current buffer according to major mode." ( interactive ) ( indent-region ( point-min ) ( point-max )))

racer

Racer is a code completion and source code navigation tool for Rust.

Install the racer crate:

λ cargo install racer

Rust source code is needed for auto-completion so clone it somewhere:

λ git clone git@github.com:rust-lang/rust.git

To use racer within emacs, do a M-x package-install racer and set it up like:

( setq racer-cmd "~/.cargo/bin/racer" ) ;; Rustup binaries PATH ( setq racer-rust-src-path "/Users/julien/Code/rust/src" ) ;; Rust source code PATH ( add-hook 'rust-mode-hook #' racer-mode ) ( add-hook 'racer-mode-hook #' eldoc-mode ) ( add-hook 'racer-mode-hook #' company-mode )

Note that racer relies on company-mode so install it if you haven’t.

flycheck-rust

flycheck is my prefered solution for on the fly syntax checking. It will compile your code in background and highlight the problematic parts.

Let’s M-x package-install flycheck-rust and then set it up like:

( add-hook 'flycheck-mode-hook #' flycheck-rust-setup )

Wrapping up

That’s all, you now have some great Rust support in your emacs with syntax highlighting, cargo handling, code formatting, errors highlighting, code-completion and source navigation. Happy Rust hacking!