bbarker/flycheck

Modern on the fly syntax checking for GNU Emacs

Flycheck

Flycheck (aka “Flymake done right”) is a modern on-the-fly syntax checking extension for GNU Emacs 24 with:

• ready-to-use syntax checkers for a bunch of languages,
• easy customization,
• a comprehensive manual,
• a dead simple, declarative API to create new syntax checkers,
• major-mode based selection of syntax checkers,
• multiple syntax checkers per buffer,
• optional error list popup,
• a “doesn’t get in your way” guarantee,
• and a clean, concise and understandable implementation with decent test coverage.

The screenshot shows Flycheck on Emacs 24.3.50 with the awesome Solarized Light color theme and the great Source Code Pro font.

Features

• Automatic on-the-fly syntax checking while editing
• Fully automatic selection of the best syntax checker
• Optional manual selection of a syntax checker with flycheck-select-checker at C-c ! s
• Built-in syntax checkers for:
  • AsciiDoc
  • C/C++
  • CFEngine
  • Chef cookbooks
  • CoffeeScript
  • CSS
  • D
  • Elixir
  • Emacs Lisp
  • Erlang
  • Go
  • Haml
  • Handlebars
  • Haskell
  • HTML
  • Javascript
  • JSON
  • LESS
  • Lua
  • Perl
  • PHP
  • Puppet
  • Python
  • Racket
  • RST (ReStructuredText)
  • Ruby
  • Rust
  • Sass
  • Scala
  • SCSS
  • Shell scripts (POSIX Shell, Bash and Zsh)
  • Slim
  • TeX/LaTeX
  • Texinfo
  • XML
  • YAML
• Nice error indication and highlighting
• Easy customization
• Syntax checker configuration with project-specific configuration files and options
• Error navigation with next-error and previous-error
• Error list with flycheck-list-errors at C-c ! l
• Declarative API to define new syntax checkers
• Error parsers for structured markup formats (e.g. Checkdoc XML)

3rd party extensions

The following extensions provide additional cool features for Flycheck:

• flycheck-cask makes Flycheck use local packages in Cask projects.
• flycheck-color-mode-line colors the mode line according to the Flycheck status.
• flycheck-hdevtools provides a Flycheck syntax checker for hdevtools.
• flycheck-d-unittest a Flycheck checker to run unit tests for D programs on the fly.

Installation

Install the ELPA package from MELPA or Marmalade. In your Cask file:

(source gnu)
(source melpa)

(depends-on "flycheck")

Flycheck supports Emacs 24. It is tested with Emacs 24.3, and Emacs snapshot builds. It should work with GNU Emacs 24.1 and 24.2 as well, but it is not tested against these versions. If it does not work with these versions, please report an issue.

Flycheck does not support Windows, but tries to be compatible with it. You may try to use Flycheck on Windows. It should mostly work, but expect problems and issues. Pull requests which improve Windows compatibility are welcome.

Flycheck also does not support GNU Emacs 23 and other flavors of Emacs (e.g. XEmacs, Aquamacs, etc.). Don't try, it will not work.

Most checkers have dependencies against external tools that perform the checking. Use C-c ! ? to see what a checker needs, e.g. C-c ! ? python-pylint.

Usage

Once installed, enable Flycheck mode with M-x flycheck-mode.

To enable Flycheck mode in all buffers, in which it can be used, add the following to your init.el file:

(add-hook 'after-init-hook #'global-flycheck-mode)

In Flycheck mode the buffer will automatically be checked on the fly, if a suitable syntax checker exists. Use C-c ! c to start a syntax check manually.

A suitable syntax checker is automatically selected from the list of registered checkers in flycheck-checkers. Use C-c ! s to manually select a specific syntax checker, or configure the syntax checker per file by setting flycheck-checker as file local variable:

# Local Variables:
# flycheck-checker: python-pylint
# End:

Read the section Syntax checker selection in the Flycheck manual for more information.

Some syntax checkers read configuration files, or provide options for customization. Use M-x customize-group RET flycheck-config-files and M-x customize-group RET flycheck-options respectively to customize these. Refer to the section Syntax checker configuration in the Flycheck manual for more information.

Errors and warnings from the syntax checker are reported in the mode line, highlighted in the buffer and indicated with icons in the fringe. Customize flycheck-highlighting-mode and flycheck-indication-mode to change the highlighting and indication of errors. Also look at M-x customize-group RET flycheck-faces to customize the visual appearance, and read Error reporting and Mode line in the Flycheck manual.

Note: The default highlighting faces provided GNU Emacs are ill-suited to highlight errors. They are too easily overlooked. Make sure to customize these faces to add a striking background color or an underlying, or choose a color theme with reasonable Flycheck faces, for instance the excellent light or dark Solarized themes, or the fancy Zenburn theme.

Use C-c ! n and C-c ! p to navigate between errors, or use C-c ! l to list all errors in a separate buffer. If the point is on an error, the error message is shown in the echo area or in a popup buffer after a short delay. You may also hover the mouse over a highlighted error to get a tooltip with the error message. Read the Error navigation section in the manual for more information.

Read the complete manual inside Emacs with C-c ! i or M-x flycheck-info, or online at http://flycheck.github.io.

Credits

Flycheck stands on the shoulders of giants, and was shaped with the help of many great people, too many to list them all in this README.

The Credits section in the manual contains a complete list of contributors and their contributors.

License

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.

See COPYING for details.