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Racer for Emacs

MELPA MELPA Stable Coverage Status

This is the official Emacs package for Racer.

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Table of Contents

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Completion

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

racer completion screenshot

You can also press <kbd>F1</kbd> 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.

racer go to definition

You can use <kbd>M-.</kbd> to go to the definition, and <kbd>M-,</kbd> to go back.

Describe Functions and Types

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

racer completion screenshot

Use <kbd>M-x racer-describe</kbd> 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 <kbd>TAB</kbd>.

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