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

Figure 1: Cargo run

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)))

Figure 2: rustfmt

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.

Figure 3: racer

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)

Figure 4: flycheck

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!