Fancy Rust development with Emacs
=================================


Rustup[0] 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:

   $ 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[1].

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[2].


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[3] 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)

Cargo run in action[8]


## rustfmt

rustfmt[4] 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:

   $ 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)))

See rustfmt in action[9]

The indent-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[5] is a code completion and source code navigation tool for
Rust.

Install the racer crate:

   $ cargo install racer

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

   $ git clone [email protected]: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[6] so install it if you
haven't.

racer in action[10]


## flycheck-rust

flycheck[7] 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)

flycheck in action[11]


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!


[0] https://www.rustup.rs
[1] https://github.com/rust-lang-nursery/rustup.rs#toolchain-specification
[2] https://github.com/rust-lang-nursery/rustup.rs
[3] http://doc.crates.io/index.html
[4] https://github.com/rust-lang-nursery/rustfmt
[5] https://github.com/phildawes/racer
[6] https://company-mode.github.io
[7] http://www.flycheck.org/en/latest/
[8] http://julienblanchard.com/assets/images/cargo-run.gif
[9] http://julienblanchard.com/assets/images/rustfmt.gif
[10] http://julienblanchard.com/assets/images/racer.gif
[11] http://julienblanchard.com/assets/images/flycheck.gif

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Last update: 14 May, 2016

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