Racer for Emacs

This is the official Emacs package for Racer.

Table of Contents

Completion

racer.el supports code completion of variables, functions and modules.

You can also press F1 to pop up a help buffer for the current completion candidate.

Note that due to a limitation of racer, racer.el cannot offer completion for macros.

Find Definitions

racer.el can jump to definition of functions and types.

You can use M-. to go to the definition, and M-, to go back.

Describe Functions and Types

racer.el can show a help buffer based on the docstring of the thing at point.

Use M-x racer-describe to open the help buffer.

Installation

1. You will need to use a nightly version of rust. If you're using rustup, run

   $ rustup toolchain add nightly
   

2. Install Racer and download the source code of Rust:

   $ rustup component add rust-src
   $ cargo +nightly install racer
   

3. Allow Emacs to install packages from MELPA:

   (require 'package)
   (add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/"))

4. Install the Emacs package for Racer: M-x package-install RET racer RET

5. Configure Emacs to activate racer when rust-mode starts:

   (add-hook 'rust-mode-hook #'racer-mode)
   (add-hook 'racer-mode-hook #'eldoc-mode)

   For completions, install company with M-x package-install RET company RET. A sample configuration:

   (add-hook 'racer-mode-hook #'company-mode)
   
   (require 'rust-mode)
   (define-key rust-mode-map (kbd "TAB") #'company-indent-or-complete-common)
   (setq company-tooltip-align-annotations t)

   For automatic completions, customize company-idle-delay and company-minimum-prefix-length.

   Racer process may be slow to respond for instance when indexing. You can customize racer-command-timeout and racer-eldoc-timeout to avoid rendering your Emacs session unresponsive. Eldoc timeout should be on the lower side and defaults to 0.5 seconds. You can probably tweak it down on a fast machine. Timeout of nil will wait indefinitely.

Testing your setup

To test completion: Open a rust file and try typing use std::io::B and press TAB.

To test go to definition: Place your cursor over a symbol and press M-. to jump to its definition.

Press C-x 4 . to jump to its definition in another window.

Press C-x 5 . to jump to its definition in another frame.

Press M-, to jump back to the previous cursor location.

If it doesn't work, try M-x racer-debug to see what command was run and what output was returned.

Tests

racer.el includes tests. To run them, you need to install Cask, then:

$ cask install
$ cask exec ert-runner