Flycheck — Syntax checking for GNU Emacs

Flycheck is a modern on-the-fly syntax checking extension for GNU Emacs, intended as replacement for the older Flymake extension which is part of GNU Emacs. For a detailed comparison to Flymake see Flycheck versus Flymake.

It uses various syntax checking and linting tools to automatically check the contents of buffers while you type, and reports warnings and errors directly in the buffer, or in an optional error list:

Out of the box Flycheck supports over 40 different programming languages with more than 80 different syntax checking tools, and comes with a simple interface to define new syntax checkers.

Many 3rd party extensions provide new syntax checkers and other features like alternative error displays or mode line indicators.

Try out

Flycheck needs GNU Emacs 24.3 or newer, and works best on Unix systems. Windows users, please be aware that Flycheck does not support Windows officially, although it should mostly work fine on Windows. See Windows support and watch out for known Windows issues!

To try Flycheck in your Emacs session install some syntax checker tools and type the following in your *scratch* buffer and run M-x eval-buffer:

(require 'package)
(add-to-list 'package-archives
             '("melpa" . "http://stable.melpa.org/packages/") t)
(package-initialize)
(package-refresh-contents)

(package-install 'flycheck)

(global-flycheck-mode)

For a permanent installation of Flycheck follow the Installation instructions. For a gentle introduction into Flycheck features go through Quickstart guide.

The User Guide

The User Guide provides installation and usage help for Flycheck. It starts with installation instructions and a quick start tutorial and then focuses on an in-depth references of all parts of Flycheck.

We are currently in the process of converting the old Texinfo manual to Sphinx. Meanwhile you can read a simple HTML version of the old manual at flycheck.html.

Todo

Port the old manual

Meanwhile see flycheck.html for a simple HTML version of the old manual.

Installation

This document gives you detailed instructions and information about installing Flycheck.

Prerequisites

Flycheck needs GNU Emacs 24.3 and works best on Unix-like systems like Linux or OS X. It does not support older releases of GNU Emacs or other flavours of Emacs (e.g. XEmacs, Aquamacs, etc.).

Windows support

Flycheck does not explicitly support Windows, but tries to maintain Windows compatibility and should generally work fine on Windows, too. However, we can neither answer questions about Windows nor fix bugs that only occur on Windows without the help of active Windows users. Please watch out for known Windows issues.

Syntax checking tools

Flycheck does not check buffers itself but relies on external programs to check buffers. These programs must be installed separately. Please take a look at the list of supported languages to find out what tools are required for a particular language.

Many of these programs are available in the package repositories of Linux distributions or in Homebrew for OS X. Others can be installed with standard package managers such as Rubygems, NPM, Cabal, etc.

Package installation

We recommend to install Flycheck with Emacs’ built-in package manager. Flycheck is available in the popular MELPA archive which provides up to date snapshots of Flycheck’s development state. The sibling repository MELPA Stable serves tagged releases of Flycheck instead. We advise to use MELPA if you are fine with weekly or even daily updates. If you would prefer longer time between releases use MELPA Stable instead.

Unfortunately neither of these repositories are available in Emacs by default. You must explicitly add them to package-archives, by adding the following to your init file:

(require 'package)
(add-to-list 'package-archives
              '("melpa" . "https://melpa.org/packages/") t)
(package-initialize)

This adds MELPA; for MELPA Stable replace https://melpa.org with https://stable.melpa.org. If you do not know where your init file is inspect the value of user-init-file with C-h v user-init-file.

Once the repository is set up you can install Flycheck from Emacs’ package menu at M-x list-packages, or directly with M-x package-install RET flycheck.

use-package

You may want to take a look at use-package which provides simple syntax to declare and configure packages in your init file. In addition to the Github README the article My Emacs configuration with use-package has more information about use-package. Specifically it allows to automatically install missing packages from package archive when Emacs starts.

Add the following form to your init file to setup Flycheck with use-package:

(use-package flycheck
  :ensure t
  :init (global-flycheck-mode))

Then press C-M-x with point somewhere in this form to install and enable Flycheck for the current Emacs session.

Alternative installation methods

Some users prefer to install Flycheck via other methods such as el-get, Git submodules, etc.

We do not support any of these methods, and advise against any alternative installation method. We do not consider it a bug if Flycheck works when installed as above but not with a different installation method.

Warning

If you install Flycheck in any way other than our official packages you do so at your own risk.

Please beware of breakage and understand that while we do not actively work against alternative installation methods we will not make compromises to support alternative installation methods. We will close issues reported for alternative installation if we fail to reproduce them with a proper installation of Flycheck.

Quickstart

This page gives a quick introduction into Flycheck and an overview of its most important features. Before you start here please make sure that Flycheck is installed.

Enable Flycheck

Now add the following code to your init file to permanently enable syntax checking with Flycheck:

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

Install syntax checker programs

Now you need to install syntax checking programs for the languages you’d like to use Flycheck with. The list of supported languages tells you which languages Flycheck supports and what programs it uses.

For instance, you can install Pylint for Python and ESLint for Javascript:

$ pip install pylint
$ npm install eslint

Check syntax in a buffer

Now you are ready to use Flycheck in a Python or Javascript buffer. Visit a Python or Javascript file and check whether your Flycheck setup is complete with C-c ! v.

If everything is green Flycheck will now start to check the buffer on the fly while you are editing. Whenever you make a mistake that the eslint or Pylint catch Flycheck will highlight the corresponding place in the buffer with an error underline whose color reflects the severity of the issue. Additionally Flycheck will put a symbol into the fringe for affected lines and show the total number of errors and warnings in the buffer in the mode line.

Navigate and list errors

With C-c ! n and C-c ! p you can now jump back and forth between erroneous places. If you keep on such a place for a little while Flycheck will show the corresponding error message in the each area. Likewise, if you hover such a place with the mouse cursor Flycheck will show the error message in a tooltip.

Press C-c ! l to pop up a list of all errors in the current buffer. This list automatically updates itself when you fix errors or introduce new ones, and follows the currently selected buffer. If the error list is selected you can type n and p to move up and down between errors and jump to their corresponding location in the buffer.

More features

All Flycheck commands are available in the Emacs Menu at Tools -‣ Syntax checking:

The menu of Flycheck, showing all available Flycheck commands

The same menu also pops up when you click on the mode line lighter:

The mode line menu of Flycheck

Check buffers

Flycheck provides two Emacs minor modes for automatic syntax checking: Flycheck Mode to enable syntax checking in the current buffer, and Global Flycheck Mode to enable syntax checking in all buffers whenever possible.

Minor Mode Flycheck Mode

Enable automatic syntax checking in the current buffer.

Minor Mode Global Flycheck Mode

Enable Flycheck Mode in all buffers where syntax checking is possible.

Note

This mode does not enable Flycheck Mode in remote files (via TRAMP) and encrypted files. Checking remote files may be very slow depending on the network connections, and checking encrypted files would leak confidential data to temporary files and subprocesses.

You can manually enable Flycheck Mode in these buffers nonetheless, but we do not recommend this for said reasons.

Add the following to your init file to enable syntax checking permanently:

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

You can exclude specific major modes from syntax checking with flycheck-global-modes:

defcustom flycheck-global-modes

Major modes for which Global Flycheck Mode turns on Flycheck Mode:

t (the default)

Turn Flycheck Mode on for all major modes.

(foo-mode …)

Turn Flycheck Mode on for all major modes in this list, i.e. whenever the value of major-mode is contained in this list.

(not foo-mode …)

Turn Flycheck Mode on for all major nodes not in this list, i.e. whenever the value of major-mode is not contained in this list.

Note

Global Flycheck Mode never turns on Flycheck Mode in major modes whose mode-class property is special, regardless of the value of this option. Syntax checking simply makes no sense in special buffers which are typically intended for non-interactive display rather than editing.

See also

Major Mode Conventions(elisp)

Information about major modes, and modes marked as special.

Check automatically

By default Flycheck Mode automatically checks a buffer whenever

• it is enabled,
• the buffer is saved,
• a new line is inserted,
• or a short time after the last change was made in a buffer.

You can customise this behaviour with flycheck-check-syntax-automatically:

defcustom flycheck-check-syntax-automatically

A list of events which trigger a syntax check in the current buffer:

save

Check the buffer immediately after it was saved.

new-line

Check the buffer immediately after a new line was inserted.

idle-change

Check the buffer a short time after the last change. The delay is customisable with flycheck-idle-change-delay:

defcustom flycheck-idle-change-delay

Seconds to wait after the last change to the buffer before starting a syntax check.

mode-enabled

Check the buffer immediately after Flycheck Mode was enabled.

For instance with the following setting Flycheck Mode will only check the buffer when it was saved:

(setq flycheck-check-syntax-automatically '(mode-enabled save))

Check manually

You can also start a syntax check explicitly with C-c ! c:

C-c ! c

M-x flycheck-buffer

Check syntax in the current buffer.

Debug syntax checking

To make sure that syntax checking works correctly verify your setup:

C-c ! v

M-x flycheck-verify-setup

Show a buffer with information about your Flycheck Mode setup for the current buffer.

Lists all syntax checkers available for the current buffer, and potential issues with their setup.

Syntax checkers

Flycheck does not check buffers on its own. Instead it delegates this task to external syntax checkers which are external programs or services that receive the contents of the current buffer and return a list of errors in the buffer, together with metadata that tells Flycheck how to run the program, how to pass buffer contents to it, and how to extract errors.

See also

Supported Languages

A complete list of all syntax checkers included in Flycheck

Like everything else in Emacs syntax checkers have online documentation which you can access with C-c ! ?:

C-c ! ?

M-x flycheck-describe-checker

Prompt for the name of a syntax checker and pop up a Help buffer with its documentation.

The documentation includes the name of the program or service used, a list of major modes the checker supports and a list of all options for this syntax checker.

Select syntax checkers automatically

Normally Flycheck automatically selects the best syntax checkers for the current buffer from flycheck-checkers whenever it needs to check the buffer:

defcustom flycheck-checkers

A list of all syntax checkers available for syntax checking.

A syntax checker in this list is a registered syntax checker.

Flycheck picks the first syntax checker from this list which exists and supports the current major mode, and runs it over the current buffer. When the checker has finished Flycheck whether it asks for a next syntax checker to run, and if so, runs the next syntax checker, and so on, until there is no more syntax checker for the current buffer. This process repeats whenever Flycheck needs to check the buffer according to flycheck-check-syntax-automatically.

For instance, the first syntax checker for Emacs Lisp is emacs-lisp which checks Emacs Lisp with Emacs’ own byte compiler. This syntax checker asks for emacs-lisp-checkdoc to run next, which checks for stylistic issues in Emacs Lisp docstrings. Thus Flycheck will first run the byte compiler and then checkdoc in an Emacs Lisp buffer.

Select syntax checkers manually

Alternatively you can tell Flycheck explicitly which syntax checker to start with in the current buffer:

C-c ! s

M-x flycheck-select-checker

Prompt for a syntax checker and use this syntax checker as the first syntax checker for the current buffer.

Flycheck may still run further syntax checkers from flycheck-checkers if the selected syntax checker asks for it.

Flycheck will use the selected syntax checker as “entry point” for syntax checks in the current buffer, just as if it had selected this syntax checker automatically. It will automatically run further syntax checkers from flycheck-checkers if the selected syntax checker asks for it.

Under the hood C-c ! s sets flycheck-checker:

defvar flycheck-checker

The name of a syntax checker to use for the current buffer.

If nil (the default) let Flycheck automatically select the best syntax checker from flycheck-checkers.

If set to a syntax checker Flycheck will use this syntax checker as the first one in the current buffer, and run subsequent syntax checkers just as if it had selected this one automatically.

If the syntax checker in this variable does not work in the current buffer signal an error.

This variable is buffer-local.

We recommend to set flycheck-checker via directory local variables to enforce a specific syntax checker for a project. For instance, Flycheck usually prefers javascript-eslint for Javascript buffers, but if your project uses javascript-jshint instead you can tell Flycheck to use javascript-jshint for all Javascript buffers of your project with the following command in the top-level directory of your project: M-x add-dir-local-variable RET js-mode RET flycheck-checker RET javascript-jshint. A new buffer pops up that shows the newly created entry in the directory variables. Save this buffer and kill it. From now on Flycheck will check all Javascript files of this project with JSHint.

See also

Locals(emacs)

General information about local variables.

Directory Variables(emacs)

Information about directory variables.

To go back to automatic selection either set flycheck-checker to nil or type C-u C-c ! s:

C-u C-c ! s

C-u M-x flycheck-select-checker

Remove any selected syntax checker and let Flycheck again select a syntax checker automatically.

Disable syntax checkers

Even if you select a checker manually Flycheck may still use a syntax checker that you’d not like to use. To completely opt out from a specific syntax checker disable it:

C-c ! x

M-x flycheck-disable-checker

Prompt for a syntax checker to disable in the current buffer.

For instance if you do not care for documentation conventions of Emacs Lisp you can opt out from emacs-lisp-checkdoc which checks your code against these conventions with C-c ! x emacs-lisp-checkdoc. After the next check all checkdoc warnings will be gone from the buffer.

Internally this command changes the buffer-local flycheck-disabled-checkers:

defcustom flycheck-disabled-checkers

A list of disabled syntax checkers. Flycheck will never use disabled syntax checkers to check a buffer.

This option is buffer-local. You can customise this variable with M-x customize-variable RET flycheck-disabled-checkers or set the default value in your init file to permanently disable specific syntax checkers. For instance:

(setq-default flycheck-disabled-checkers '(c/c++-clang))

will permanently disable c/c++-clang in all buffers.

You can also disable syntax checkers per project with directory local variables. For instance type M-x add-dir-local-variable RET emacs-lisp-mode RET flycheck-disabled-checkers RET emacs-lisp-checkdoc in your user emacs directory to disable emacs-lisp-checkdoc for all Emacs Lisp files in your personal configuration.

See also

Locals(emacs)

General information about local variables.

Directory Variables(emacs)

Information about directory variables.

To enable a disabled checker again, remove it from flycheck-disabled-checkers or use C-u C-c ! x:

C-u C-c ! x

C-u M-x flycheck-disable-checker

Prompt for a disabled syntax checker to enable again in the current buffer.

See errors in buffers

When a syntax check in the current buffer has finished Flycheck reports the results of the check in the current buffer in two ways:

• Highlight errors, warnings, etc. directly in the buffer according to flycheck-highlighting-mode.
• Indicate errors, warnings, etc. in the fringe according to flycheck-indication-mode.

Additionally Flycheck indicates its current state and the number of errors and warnings in the mode line.

The following screenshot illustrates how this looks like in the default Emacs color theme. It shows an info, a warning and an error annotation, from top to bottom. Please also note the fringe indicators on the left side and the emphasized mode line indicator in the bottom right corner:

Note

The colours of fringe icons and the whole appearance of the error highlights depend on the active color theme. Although red, orange and green or blue seem to be somewhat standard colours for Flycheck’s annotations across many popular themes, please take a closer look at your color theme if you’re in doubt about the meaning of a Flycheck highlight.

Error levels

All errors that syntax checkers report have a level which tells you the severity of the error. Flycheck has three built-in levels:

error

Severe errors like syntax or type errors.

warning

Potential but not fatal mistakes which you should likely fix nonetheless.

info

Purely informational messages which inform about notable things in the current buffer, or provide additional help to fix errors or warnings.

Each error level has a distinct highlighting and colour which helps you to identify the severity of each error right in the buffer.

Error highlights

Flycheck highlights errors directly in the buffer according to flycheck-highlighting-mode. By default these highlights consist of a coloured wave underline which spans the whole symbol at the error location as in the screenshot above but the highlights are entirely customisable. You can change the extents of highlighting or disable it completely with flycheck-highlighting-mode, or customise Flycheck’s faces to change the style of the underline or use different colours.

defcustom flycheck-highlighting-mode

How Flycheck highlights errors and warnings in the buffer:

nil

Do not highlight anything at all.

lines

Highlight the whole line and discard any information about the column.

columns

Highlight the column of the error if any, otherwise like lines.

symbols

Highlight the entire symbol around the error column if any, otherwise like columns. This is this default.

sexps

Highlight the entire expression around the error column if any, otherwise like columns.

Warning

In some major modes sexps is very slow, because discovering expression boundaries efficiently is hard.

The built-in python-mode is known to suffer from this issue.

Be careful when enabling this mode.

The highlights use the following faces depending on the error level:

defface flycheck-error

defface flycheck-warning

defface flycheck-info

The highlighting face for error, warning and info levels respectively.

Fringe icons

In GUI frames Flycheck also adds indicators to the fringe—the left or right border of an Emacs window that is—to help you identify erroneous lines quickly. These indicators consist of a rightward-pointing double arrow shape coloured in the colour of the corresponding error level.

Note

Flycheck extensions can define custom error levels with different fringe indicators. Furthermore some Emacs distributions like Spacemacs redefine Flycheck’s error levels to use different indicators. If you’re using such a distribution please take a look at its documentation if you’re unsure about the appearance of Flycheck’s indicators.

Note that we discourage you from changing the shape of Flycheck’s fringe indicators.

You can customise the location of these indicators (left or right fringe) with flycheck-indication-mode which also lets you turn off these indicators completely:

defcustom flycheck-indication-mode

How Flycheck indicates errors and warnings in the buffer fringes:

left-fringe or right-fringe

Use the left or right fringe respectively.

nil

Do not indicate errors and warnings in the fringe.

The following faces control the colours of the fringe indicators. However they do not let you change the shape of the indicators—to achieve this you’d have to redefine the error levels with flycheck-define-error-level.

defface flycheck-fringe-error

defface flycheck-fringe-warning

defface flycheck-fringe-info

The icon faces for error, warning and info levels respectively.

Mode line

Like all minor modes Flycheck also has a mode line indicator. You can see it in the bottom right corner of the above screenshot. By default the indicator shows Flycheck’s current state via one of the following texts:

FlyC*	Flycheck is checking the buffer currently.
FlyC	There are no errors or warnings in the current buffer.
FlyC:3/5	There are three errors and five warnings in the current buffer.
FlyC-	Flycheck did not find a syntax checker for the current buffer. Take a look at the list of supported languages and type C-c ! v to see what checkers are available for the current buffer.
FlyC!	The last syntax check failed. Inspect the *Messages* buffer look for error messages, and consider reporting a bug.
FlyC?	The last syntax check had a dubious result. The definition of a syntax checker may have a bug. Inspect the *Messages* buffer and consider reporting a bug.

You can entirely customise the mode line indicator with flycheck-mode-line:

flycheck-mode-line

A “mode line construct” for Flycheck’s mode line indicator.

See also

Mode Line Data(elisp)

Documentation of mode line constructs.

flycheck-status-emoji

A Flycheck extension which puts emojis into Flycheck’s mode line indicator.

flycheck-color-mode-line

A Flycheck extension which colours the entire mode line according to Flycheck’s status.

Error thresholds

To avoid flooding a buffers with excessive highlighting, cluttering the appearance and slowing down Emacs, Flycheck takes precautions against syntax checkers that report a large number of errors exceeding flycheck-checker-error-threshold:

defcustom flycheck-checker-error-threshold

The maximum number of errors a syntax checker is allowed to report.

If a syntax checker reports more errors the error information is discarded. To not run into the same issue again on the next syntax check the syntax checker is automatically added to flycheck-disabled-checkers in this case to disable it for the next syntax check.

Clear results

You can explicitly remove all highlighting and indication and all error information from a buffer:

C-c ! C

M-x flycheck-clear

Clear all reported errors, all highlighting and all indication icons from the current buffer.

C-u C-c ! C

C-u M-x flycheck-clear

Like C-c ! C but also interrupt any syntax check currently running. Use this command if you think that Flycheck is stuck.

List all errors

You can see all errors in the current buffer in Flycheck’s error list:

The key C-c ! l pops up the error list:

C-c ! l

M-x flycheck-list-errors

M-x list-flycheck-errors

Pop up a list of errors in the current buffer.

The error list automatically updates itself after every syntax check and follows the current buffer: If you switch to different buffer or window it automatically shows the errors of the now current buffer. The buffer whose errors are shown in the error list is the source buffer.

Whenever the point is on an error in the source buffer the error list highlights these errors—the green line in the screenshot above.

Within the error list the following key bindings are available:

RET	Go to the current error in the source buffer
n	Jump to the next error
p	Jump to the previous error
f	Filter the error list by level
F	Remove the filter
S	Sort the error list by the column at point
g	Check the source buffer and update the error list
q	Quit the error list and hide its window

Filter the list

By the default the error list shows all errors but sometimes you’d like to hide warnings to focus only on real errors. The error list lets you hide all errors below a certain level with f. This key prompts for an error level and will remove all errors of lower levels from the list. The filter is permanent as long as the error list buffer stays alive or the filter is reset with F.

Sort the list

You can press S or click on the column headings to sort the error list by any of the following columns:

• Line
• Level
• ID
• Message and checker

Click twice or press S repeatedly to flip the sort order from ascending to descending or vice versa.

Tune error list display

By default the error list buffer pops up like any other buffer. Flycheck does not enforce special rules on how it’s displayed and where it’s located in the frame so essentially the error list pops up at arbitrary places wherever Emacs can find a window for it.

However you can tell Emacs to obey certain rules when displaying buffers by customizing the built-in option display-buffer-alist. You can use this option to make the error list display like similar lists in contemporary IDEs like VisualStudio, Eclipse, etc. with the following code in your init file:

(add-to-list 'display-buffer-alist
             (,(rx bos "*Flycheck errors*" eos)
              (display-buffer-reuse-window
               display-buffer-in-side-window)
              (side            . bottom)
              (reusable-frames . visible)
              (window-height   . 0.33)))

This display rule tells Emacs to always display the error list at the bottom side of the frame, occupying a third of the entire height of the frame.

See also

Shackle

An Emacs package which provides an alternative way to control buffer display

Interact with errors

There are a couple of things that you can do with Flycheck errors in a buffer:

• You can navigate to errors, and go to the next or previous error.
• You can display errors to read their error messages.
• You can put error messages and IDs into the kill ring.

This section documents the corresponding commands and their customisation options.

Navigate errors

By default Flycheck hooks into Emacs’ standard error navigation on M-g n (next-error) and M-g p (previous-error). When Flycheck Mode is enabled these commands will jump to the next and previous Flycheck error respectively. See Compilation Mode(emacs) for more information about these commands.

This way you don’t need to learn special keybindings to navigate Flycheck errors; navigation should just work out of the box.

Note

Visible compilation buffers such as buffers from M-x compile, M-x grep, etc. still take precedence over Flycheck’s errors.

The exact behaviour of these error navigation features is very context-dependent and can be very confusing at times so you can disable this integration:

defcustom flycheck-standard-error-navigation

Whether to integrate Flycheck errors into Emacs’ standard error navigation. Defaults to t, set to nil to disable.

Important

When changing the value you must disable Flycheck Mode and enable it again for the change to take effect in any buffers where Flycheck Mode is enabled.

Flycheck provides an independent set of navigation commands which will always navigate Flycheck errors in the current buffer, regardless of visible compilation buffers and flycheck-standard-error-navigation:

C-c ! n

M-x flycheck-next-error

Jump to the next error.

With prefix argument jump forwards by as many errors as specified by the prefix argument, e.g. M-3 C-c ! n will move to the 3rd error from the current point. With negative prefix argument move to previous errors instead. Signal an error if there are no more Flycheck errors.

C-c ! p

M-x flycheck-previous-error

Jump to the previous Flycheck error.

With prefix argument jump backwards by as many errors as specified by the prefix argument, e.g. M-3 C-c ! p will move to the 3rd error before the current point. With negative prefix argument move to next errors instead. Signal an error if there are no more Flycheck errors.

M-x flycheck-first-error

Jump to the first Flycheck error.

With prefix argument, jump forwards to by as many errors as specified by the prefix argument, e.g. M-3 M-x flycheck-first-error moves to the 3rd error from the beginning of the buffer. With negative prefix argument move to the last error instead.

By default error navigation jumps to all errors but you can choose to skip over errors with low levels:

defcustom flycheck-navigation-minimum-level

The minimum levels of errors to consider for navigation.

If set to an error level only navigate to errors whose level is as least as severe as this one. If nil navigate to all errors.

Display errors

Whenever you move point to an error location Flycheck automatically displays all Flycheck errors at point after a short delay which you can customise:

defcustom flycheck-display-errors-delay

The number of seconds to wait before displaying the error at point. Floating point numbers can express fractions of seconds.

By default Flycheck shows the error messages in the minibuffer or in a separate buffer if the minibuffer is too small to hold the whole error message but this behaviour is entirely customisable:

defcustom flycheck-display-errors-function

A function to display errors.

The function is given the list of Flycheck errors to display as sole argument and shall display these errors to the user in some way.

Flycheck provides two built-in functions for this option:

defun flycheck-display-error-messages errors

defun flycheck-display-error-messages-unless-error-list errors

Show error messages and IDs in the echo area or in a separate buffer if the echo area is too small (using display-message-or-buffer which see). The latter only displays errors when the error list is not visible. To enable it add the following to your init file:

(setq flycheck-display-errors-function
      #'flycheck-display-error-messages-unless-error-list)

See also

flycheck-pos-tip

A Flycheck extension to display errors in a GUI popup.

Additionally Flycheck shows errors in a GUI tooltip whenever you hover an error location with the mouse pointer. By default the tooltip contains the messages and IDs of all errors under the pointer, but the contents are customisable:

defcustom flycheck-help-echo-function

A function to create the contents of the tooltip.

The function is given a list of Flycheck errors to display as sole argument and shall return a single string to use as the contents of the tooltip.

Kill errors

You can put errors into the kill ring with C-c ! w:

C-c ! w

M-x flycheck-copy-errors-as-kill

Copy all messages of the errors at point into the kill ring.

C-u C-c ! w

C-u M-x flycheck-copy-errors-as-kill

Like C-c ! w but with error IDs.

M-0 C-c ! w

M-0 M-x flycheck-copy-errors-as-kill

Like C-c ! w but do not copy the error messages but only the error IDs.

Flycheck versus Flymake

This article provides information about Flycheck compares to the built-in Flymake mode. It does not consider third-party extensions such as flymake-easy or flymake-cursor, but references them at appropriate places.

We aim for this comparison to be neutral and complete, but do not provide any guarantee for completeness or correctness of the following information. Moreover, we consider Flycheck superior to Flymake in all aspects. As such, you may find this page biased towards Flycheck. Please excuse this as well as any factual mistake or lack of information. Please suggest improvements.

Important

This comparison was written around the time Emacs 24.5 was released, and only updated infrequently since then. Flycheck has changed and hopefully improved meanwhile, and Flymake may have done so as well. As such parts of this article may be outdated and have become incorrect by now. Likewise screenshots that show particular behaviour of Flycheck or Flymake have aged; the corresponding features of Flycheck and Flymake may look different now, or have gone altogether.

Please report any incorrectness and any inconsistency you find, and feel free to edit this page and improve it.

Overview

This table intends to give an overview about the differences and similarities between Flycheck and the default install of Flymake. It is not a direct comparison to third-party extensions like flymake-easy or flymake-cursor. For a more comprehensive look compared to those extensions, please read the details in the main article and the footnotes.

Please do not use this table alone to make your personal judgment. Read the detailed review in the following sections, too, at least with regards to the features you are interested in.

	Flycheck	Flymake
Supports Emacs versions	24.3	22+
Built-in	no [1]	yes
Enables automatically if possible	yes	no
Checks after	save, newline, change	newline, change
Checks in background	yes	yes
Automatic syntax checker selection	By major mode and custom predicates	By file name patterns [2]
Manual syntax checker selection	yes	no
Multiple syntax checkers per buffer	yes	no [3]
Supported languages	>40	~5 [4]
Checking remote files via Tramp	said to work, but not officially supported [5]	partly?
Definition of new syntax checkers	Single declarative function/macro	Function definition and various variables [6]
Functions as syntax checkers	yes	no [7]
Error levels	errors, warnings, informational, custom levels	errors, warnings
Error identifiers	yes	no
Error parsing	Regular expressions, custom parsers for structured formats (XML, JSON, etc.)	Regular expressions
Multiline error messages	yes	no
Error highlighting in buffers	yes	yes
Fringe icons for errors	yes	yes (Emacs 24.1+)
Error message display	Tooltip, echo area, fully customizable	Tooltip only [8]
List of all errors	yes	no
Resource consumption	low	high
Unit tests	all syntax checkers, large parts of internals	none?

Detailed review

Relation to Emacs

Flymake is part of GNU Emacs since GNU Emacs 22. As such, contributions to Flymake are subject to the FSF policies on GNU projects. Most notably, contributors are required to assign their copyright to the FSF by signing a contributor agreement.

Flycheck is not part of GNU Emacs, and is unlikely to ever be (see issue 801). However, it is free software as well, and publicly developed on the well-known code hosting platform Github. Contributing to Flycheck does not require a copyright assignments.

Enabling syntax checking

Flymake is not enabled automatically for supported languages. It must be be enabled for each mode individually and carefully, because it does not deal well with unavailable syntax checker tools. In a GUI frame, it signals errors in GUI dialogs. In a TTY frame, it does not signal any error at all, but instead silently hangs. The same occurs when a syntax checker tool becomes unavailable after Flymake Mode is enabled (for instance, because the underlying tool was uninstalled).

Flymake showing a GUI dialog to inform that a syntax checker tool is not available

The third-party library flymake-easy provides an alternate way to enable Flymake Mode, which gracefully handles unavailable syntax checkers. It does not check whether the tool still exists before a syntax check, though, and thus does still exposes above behavior when a tool becomes unavailable after the mode was enabled.

Flycheck provides a global mode global-flycheck-mode, which enables syntax checking in every supported language. If a syntax checking tool is not available Flycheck fails gracefully, does not enable syntax checking, and just indicates the failure in the mode line.

Syntax checkers

Flymake supports Java, Makefiles, Perl, PHP, TeX/LaTeX and XML. Notably, it does not support Emacs Lisp. However, there are many recipes for other languages on the Flymake page in the EmacsWiki and many extension packages for other languages in the popular ELPA archive MELPA.

Flycheck provides support for over 40 languages with over 70 syntax checkers, most of them contributed by the community. Notably, Flycheck does not support Java and Makefiles.

Definition of new syntax checkers

Flymake does not provide a single function to define a new syntax checker. Instead, one has to define an “init” function, which returns the command, and add this function to flymake-allowed-file-name-masks. Additionally, one has to add the error patterns to flymake-err-line-patterns. As such, defining a syntax checker is difficult for users who are not familiar with Emacs Lisp. flymake-easy provides an easier way to define new syntax checkers, though.

Flycheck provides a single function flycheck-define-checker to define a new syntax checker. This function uses a declarative syntax which is easy to understand even for users unfamiliar with Emacs Lisp. In fact most syntax checkers in Flycheck were contributed by the community.

For example, the Perl checker in Flymake is defined as follows:

(defun flymake-perl-init ()
  (let* ((temp-file   (flymake-init-create-temp-buffer-copy
                       'flymake-create-temp-inplace))
         (local-file  (file-relative-name
                       temp-file
                       (file-name-directory buffer-file-name))))
    (list "perl" (list "-wc " local-file))))

(defcustom flymake-allowed-file-name-masks
  '(;; …
    ("\\.p[ml]\\'" flymake-perl-init)
    ;; …
    ))

(defvar flymake-err-line-patterns
  (append
   '(;; …
     ;; perl
     ("\\(.*\\) at \\([^ \n]+\\) line \\([0-9]+\\)[,.\n]" 2 3 nil 1)
     ;; …
     )
   ;; …
   ))

Whereas Flycheck’s definition of the same checker looks like this:

(flycheck-define-checker perl
  "A Perl syntax checker using the Perl interpreter.

See URL `http://www.perl.org'."
  :command ("perl" "-w" "-c" source)
  :error-patterns
  ((error line-start (minimal-match (message))
          " at " (file-name) " line " line
          (or "." (and ", " (zero-or-more not-newline))) line-end))
  :modes (perl-mode cperl-mode))

Functions as syntax checkers

Flymake cannot check a buffer with a custom Emacs Lisp function.

Flycheck provides the flycheck-define-generic-checker function to define a syntax checker based on an arbitrary Emacs Lisp function. Flycheck supports synchronous as well as asynchronous functions, and provides simple callback-based protocol to communicate the status of syntax checks. This allows Flycheck to use persistent background processes for syntax checking. For instance, flycheck-ocaml uses a running Merlin process to check OCaml buffers. This is much easier and faster than invoking the OCaml compiler.

Customization of syntax checkers

Flymake does not provide built-in means to customize syntax checkers. Instead, when defining a new syntax checker the user needs to declare customization variables explicitly and explicitly check their value in the init function.

Flycheck provides built-in functions to add customization variables to syntax checkers and splice the value of these variables into the argument list of a syntax checking tool. Many syntax checkers in Flycheck provide customization variables. For instance, you can customize the enabled warnings for C with flycheck-clang-warnings. Flycheck also tries to automatically find configuration files for syntax checkers.

Executables of syntax checkers

Flymake does not provide built-in means to change the executable of a syntax checker.

Flycheck implicitly defines a variable to set the path of a syntax checker tool for each defined syntax checker and provides the interactive command flycheck-set-checker-executable to change the executable used in a buffer.

Syntax checker selection

Flymake selects syntax checkers based on file name patterns in flymake-allowed-file-name-masks. Effectively this duplicates the existing logic Emacs uses to choose the right major mode, but lacks its flexibility and power. For instance, Flymake cannot pick a syntax checker based on the shebang of a file.

Flycheck uses the major mode to select a syntax checker. This reuses the existing sophisticated logic Emcas uses to choose and configure major modes. Flycheck can easily select a Python syntax checker for a Python script without file extension, but with proper shebang, simply because Emacs correctly chooses Python Mode for such a file.

Custom predicates

Flymake does not allow for custom predicates to implement more complex logic for syntax checker selection. For instance, Flymake cannot use different syntax checkers for buffer depending on the value of a local variable.

However, flymake-easy patches Flymake to allow for custom syntax checkers per buffer. This does not happen automatically though. The user still needs to explicitly register a syntax checker in a major mode hook.

Flycheck supports custom predicate function. For instance, Emacs uses a single major mode for various shell script types (e.g. Bash, Zsh, POSIX Shell, etc.), so Flycheck additionally uses a custom predicate to look at the value of the variable sh-shell in Sh Mode buffers to determine which shell to use for syntax checking.

Manual selection

Flymake does not provide means to manually select a specific syntax checker, either interactively, or via local variables.

Flycheck provides the local variable flycheck-checker to explicitly use a specific syntax checker for a buffer and the command flycheck-select-checker to set this variable interactively.

Multiple syntax checkers per buffer

Flymake can only use a single syntax checker per buffer. Effectively, the user can only use a single tool to check a buffer, for instance either PHP Mess Detector or PHP CheckStyle. Third party extensions to Flycheck work around this limitation by supplying custom shell scripts to call multiple syntax checking tools at once.

Flycheck can easily apply multiple syntax checkers per buffer. For instance, Flycheck will check PHP files with PHP CLI first to find syntax errors, then with PHP MessDetector to additionally find idiomatic and semantic errors, and eventually with PHP CheckStyle to find stylistic errors. The user will see all errors reported by all of these utilities in the buffer.

Errors

Error levels

Flymake supports error and warning messages. The pattern of warning messages is hard-coded in Emacs 24.3, and only became customizable in upcoming Emacs 24.4. The patterns to parse messages are kept separate from the actual syntax checker.

Flycheck supports error, warning and info messages. The patterns to parse messages of different levels are part of the syntax checker definition, and thus specific to each syntax checker. Flycheck allows to define new error levels for use in custom syntax checkers with flycheck-define-error-level.

Error identifiers

Flymake does not support unique identifiers for different kinds of errors.

Flycheck supports unique identifiers for different kinds of errors, if a syntax checker provides these. The identifiers appear in the error list and in error display, and can be copied independently, for instance for use in an inline suppression comment or to search the web for a particular kind of error.

Error parsing

Flymake parses the output of syntax checker tools with regular expressions only. As it splits the output by lines regardless of the regular expressions, it does not support error messages spanning multiple lines (such as returned by the Emacs Lisp byte compiler or by the Glasgow Haskell Compiler).

flymake-easy overrides internal Flymake functions to support multiline error messages.

Flycheck can use regular expressions as well as custom parsing functions. By means of such functions, it can parse JSON, XML or other structured output formats. Flycheck includes some ready-to-use parsing functions for well-known output formats, such as Checkstyle XML. By parsing structured output format, Flycheck can handle arbitrarily complex error messages. With regular expressions it uses the error patterns to split the output into tokens and thus handles multiline messages just as well.

Error message display

Flymake error message in tooltip

Flycheck error message in tooltip and echo area

In GUI frames, Flymake shows error messages in a tool tip, if the user hovers the mouse over an error location. It does not provide means to show error messages in a TTY frame, or with the keyboard only.

The third-party library flymake-cursor shows Flymake error messages at point in the echo area, by overriding internal Flymake functions.

Flycheck shows error message tool tips as well, but also displays error messages in the echo area, if the point is at an error location. This feature is fully customizable via flycheck-display-errors-function.

Error list

Flymake does not provide means to list all errors in the current buffer.

Flycheck can list all errors in the current buffer in a separate window. This error list is automatically updated after each syntax check, and follows the focus.

Listing all errors in the current buffer

Resource consumption

Syntax checking

Flymake starts a syntax check after every change, regardless of whether the buffer is visible in a window or not. It does not limit the number of concurrent syntax checks. As such, Flymake starts many concurrent syntax checks when many buffers are changed at the same time (e.g. after a VCS revert), which is known to freeze Emacs temporarily.

Flycheck does not conduct syntax checks in buffers which are not visible in any window. Instead it defers syntax checks in such buffers until after the buffer is visible again. Hence, Flycheck does only start as many concurrent syntax checks as there are visible windows in the current Emacs session.

Checking for changes

Flymake uses a separate timer (in flymake-timer) to periodically check for changes in each buffer. These timers run even if the corresponding buffers do not change. This is known to cause considerable CPU load with many open buffers.

Flycheck does not use timers at all to check for changes. Instead it registers a handler for Emacs’ built-in after-change-functions hook which is run after changes to the buffer. This handler is only invoked when the buffer actually changed and starts a one-shot timer to delay the syntax check until the editing stopped for a short time, to save resources and avoid checking half-finished editing.

Unit tests

Flymake does not appear to have a test suite at all.

Flycheck has unit tests for all built-in syntax checkers, and for large parts of the underlying machinery and API. Contributed syntax checkers are required to have test cases. A subset of the test suite is continuously run on Travis CI.

Footnotes

[1]	Flycheck is unlikely to ever become part of Emacs, see issue 801.

[2]	The 3rd party library flymake-easy allows to use syntax checkers per major mode.

[3]	Various 3rd party packages thus use custom shell scripts to call multiple syntax checking tools at once.

[4]	However, the Flymake page in the EmacsWiki provides recipes for many other languages, although of varying quality. Furthermore, the popular ELPA archive MELPA provides many packages which add more languages to Flymake.

[5]	See for instance this comment.

[6]	flymake-easy provides a function to define a new syntax checker, which sets all required variables at once.

[7]	flymake-easy overrides internal functions of Flymake to add support for multiline error messages.

[8]	The 3rd party library flymake-cursor shows Flymake error messages at point in the echo area.

The Developer Guide

The Developer Guide shows how to write syntax checkers for Flycheck and how to extend Flycheck.

Todo

Port the extending section from the old manual

Meanwhile see flycheck.html for a simple HTML version of the old manual.

The Community Guide

The Community Guide provides information about Flycheck’s ecosystem and community.

Flycheck Code of Conduct

Our Code of Conduct defines the social norms and policies within Flycheck’s community. Whenever you interact with Flycheck or Flycheck developers, whether in our official channels or privately, you’re expected to follow this Code of Conduct.

Conduct

Contact: Any moderator

• We are committed to providing a friendly, safe and welcoming environment for all, regardless of level of experience, gender, gender identity and expression, sexual orientation, disability, personal appearance, body size, race, ethnicity, age, religion, nationality, or similar personal characteristic.
• Please avoid using overtly sexual nicknames or other nicknames that might detract from a friendly, safe and welcoming environment for all.
• Please be kind and courteous. There’s no need to be mean or rude.
• Please do not curse or use bad words. Foul language will not help us to build a great product.
• Respect that people have differences of opinion and that every design or implementation choice carries a trade-off and numerous costs. There is seldom a right answer.
• Please keep unstructured critique to a minimum. If you have solid ideas you want to experiment with, make a fork and see how it works.
• We will exclude you from interaction if you insult, demean or harass anyone. That is not welcome behaviour. We interpret the term “harassment” as including the definition in the Citizen Code of Conduct; if you have any lack of clarity about what might be included in that concept, please read their definition. In particular, we don’t tolerate behavior that excludes people in socially marginalized groups.
• Private harassment is also unacceptable. No matter who you are, if you feel you have been or are being harassed or made uncomfortable by a community member, please contact a moderator immediately. Whether you’re a regular contributor or a newcomer, we care about making this community a safe place for you and we’ve got your back.
• Likewise any spamming, trolling, flaming, baiting or other attention-stealing behaviour is not welcome.

Moderation

These are the policies for upholding our community’s standards of conduct in our communication channels, most notably in Flycheck’s Github organisation and in Flycheck’s Gitter channels.

1. Remarks that violate the Flycheck code of conduct, including hateful, hurtful, oppressive, or exclusionary remarks, are not allowed.
2. Remarks that moderators find inappropriate, whether listed in the code of conduct or not, are also not allowed.
3. Moderators will first respond to such remarks with a warning.
4. If the warning is unheeded, the user will be “kicked,” i.e., kicked out of the communication channel to cool off.
5. If the user comes back and continues to make trouble, they will be banned, i.e., indefinitely excluded.
6. Moderators may choose at their discretion to un-ban the user if it was a first offense and they offer the offended party a genuine apology.
7. If a moderator bans someone and you think it was unjustified, please take it up with that moderator, or with a different moderator, in private. Complaints about bans in-channel are not allowed.
8. Moderators are held to a higher standard than other community members. If a moderator creates an inappropriate situation, they should expect less leeway than others.

In the Flycheck community we strive to go the extra step to look out for each other. Don’t just aim to be technically unimpeachable, try to be your best self. In particular, avoid flirting with offensive or sensitive issues, particularly if they’re off-topic; this all too often leads to unnecessary fights, hurt feelings, and damaged trust; worse, it can drive people away from the community entirely.

And if someone takes issue with something you said or did, resist the urge to be defensive. Just stop doing what it was they complained about and apologize. Even if you feel you were misinterpreted or unfairly accused, chances are good there was something you could have communicated better — remember that it’s your responsibility to make your fellow Flycheck people comfortable. Everyone wants to get along and we are all here first and foremost because we want to talk about cool technology. You will find that people will be eager to assume good intent and forgive as long as you earn their trust.

—

Adapted from the Rust Code of Conduct.

Copyright (c) 2015 Sebastian Wiesner and Flycheck contributors

Copyright (c) 2014 The Rust Project Developers

Recommended extensions

The Emacs community has produced a number of extensions to Flycheck. This page lists all that we know of and can safely recommend to our users.

Official extensions are (co-)maintained by the Flycheck maintainers who will take care to update official extensions in case of breaking changes in Flycheck and work to provide extra API for extensions if needed. If you’d like to make your extension an official one and move it into the Flycheck Github organisation please contact a maintainer.

If you do know extensions not in this list, or would like to see your own extension here, please feel free to add it.

We would like to thank all people who created and contributed to Flycheck extensions for their awesome work. Without your help and support Flycheck would not be what it is today.

User interface

These extensions change Flycheck’s user interface:

• flycheck-color-mode-line (official) colors the mode line according to the Flycheck status.
• flycheck-pos-tip (official) shows Flycheck error messages in a graphical popup.
• liblit/flycheck-status-emoji adds cute emoji (e.g. 😱 for errors) to Flycheck’s mode line status.

Language support

These extensions add support for new languages, or improve support for built-in languages. They are grouped by the corresponding language so you can jump directly to the languages that interest you:

Cadence

• cmarqu/flycheck-hdl-irun adds a syntax checker for hardware description languages supported by Cadence IES/irun.

Clojure

• clojure-emacs/squiggly-clojure adds syntax checking for Clojure.

C/C++/Objective C

• Wilfred/flycheck-pkg-config configures Flycheck to use settings from pkg-config when checking C/C++.
• flycheck-google-cpplint (official) adds a syntax checker for Google’s C++ style checker.
• Sarcasm/flycheck-irony adds a Flycheck syntax checker for C, C++ and Objective C using Irony Mode.

D

• flycheck-d-unittest (official) adds a Flycheck checker to run unit tests for D programs on the fly.

Elixir

• tomekowal/flycheck-mix adds an Elixir syntax checker using the mix build tool.

Emacs Lisp

• flycheck-cask (official) makes Flycheck use Cask packages for Emacs Lisp syntax checking in Cask projects.
• purcell/flycheck-package checks Emacs Lisp packages for common problems with package metadata.

Haskell

• flycheck-haskell (official) configures Flycheck from the Cabal settings and sandbox in Haskell projects.

Ledger

• purcell/flycheck-ledger adds a syntax checker for the Ledger accounting tool.

Mercury

• flycheck-mercury (official) adds a syntax checker for the Mercury language.

OCaml

• flycheck-ocaml (official) adds a syntax checker for OCaml using the Merlin backend.

Python

• Wilfred/flycheck-pyflakes adds a Python syntax checker using Pyflakes.

Rust

• flycheck-rust (official) configures Flycheck according to the Cargo settings and layouts of the current Rust project.

Shell scripts

• Gnouc/flycheck-checkbashisms adds a shell script syntax checker using checkbashisms which is part of Debian devscripts and checks for common Bash constructs in POSIX shell scripts.

Get help

Follow @emacs_flycheck on Twitter for updates. Feel free to mention the account for questions.

Please ask questions about Flycheck on Stack Exchange or in our Gitter chat. We try to answer all questions as fast and as precise as possible.

To report bugs and problems please please use our issue tracker. Please note that we have a special policy for Windows-only issues.

Please follow our Code of Conduct in all these places.

People

Teams

Maintainers

• Sebastian Wiesner (lunaryorn, owner, GPG key 5C42FE98)
• Clément Pit–Claudel (cpitclaudel, owner)

We maintain Flycheck and all official extensions within the Flycheck organisation, and set the direction and scope of Flycheck. We review and accept pull requests and feature proposals and fix bugs in Flycheck.

Emphasized users are also owners of the Flycheck Organisation, and thus have administrative privileges for all repositories in Flycheck. Notably only owners can currently make Flycheck releases, and their GPG keys sign release tags for Flycheck.

Mention with @flycheck/maintainers.

Moderators

Our moderators help uphold our Flycheck Code of Conduct. Currently, we do not have a dedicated moderation team; all our Maintainers also serve as moderators in our Github organisation and in our official communication channels.

Mention with @flycheck/moderators.

Note

If you’d like to help out with moderation, please contact a maintainer.

Language teams

These teams provide support for particular languages in Flycheck.

Elixir

• Kári Tristan Helgason (kthelgason)

Mention with @flycheck/elixir.

Go

• Dominik Honnef (dominikh)

Mention with @flycheck/go.

Haskell

• Sergey Vinokurov (sergv)

Mention with @flycheck/haskell.

Javascript

• Saša Jovanić (Simplify)

Mention with @flycheck/javascript.

Puppet

• Romanos Skiadas (rski)

Mention with @flycheck/puppet.

Rust

• fmdkdd
• Michael Pankov (mkpankov)

Mention with @flycheck/rust.

TypeScript

• Saša Jovanić (Simplify)

Mention with @flycheck/typescript.

Acknowledgements

We would also like to thank the following people and projects:

• Bozhidar Batsov (bbatsov) for his valuable feedback and his constant support and endorsement of Flycheck from the very beginning. Notably he added Flycheck to his popular Prelude project at a very early stage and thus brought Flycheck to many new users.
• Magnar Sveen (magnars) for his dash.el and s.el libraries, which support considerable parts of Flycheck internals, and greatly helped to overcome Sebastian’s initial aversion to Emacs Lisp.
• Martin Grenfell (scrooloose) for the Vim syntax checking extension Syntastic which saved Sebastian’s life back when he was using Vim, and served as inspiration for Flycheck and many of its syntax checkers.
• Matthias Güdemann (mgudemann), for his invaluable work on Flycheck’s logo.
• Pavel Kobyakov for his work on GNU Flymake, which is a great work on its own, despite its flaws and weaknesses.
• Simon Carter (bbbscarter), for his patient in-depth testing of automatic syntax checking, and his very constructive feedback.
• Steve Purcell (purcell) for his valuable feedback, the fruitful discussions and his important ideas about the shape and design of Flycheck, and his indispensible and dedicated work on MELPA, which drives the continuous distribution of Flycheck to its users.

Contributors

The following people—listed in alphabetical order—contributed substantial code to Flycheck:

• Alain Kalker (ackalker)
• Alex Reed (acr4)
• Atila Neves (atilaneves)
• Bozhidar Batsov (bbatsov)
• Clément Pit–Claudel (cpitclaudel, maintainer, owner)
• Cristian Capdevila (capdevc)
• Damon Haley (dhaley)
• David Caldwell (caldwell)
• David Holm (dholm)
• Deokhwan Kim (dkim)
• Derek Chen-Becker (dchenbecker)
• Derek Harland (donkopotamus)
• Dominik Honnef (dominikh)
• Doug MacEachern (dougm)
• Drew Wells (drewwells)
• Erik Hetzner (egh)
• Fanael Linithien (Fanael)
• fmdkdd
• Fred Morcos (fredmorcos)
• Gereon Frey (gfrey)
• Gulshan Singh (gsingh93)
• Iain Beeston (iainbeeston)
• Ibrahim Awwal (ibrahima)
• Jackson Ray Hamilton (jacksonrayhamilton)
• Jim Hester (jimhester)
• Jimmy Yuen Ho Wong (wyuenho)
• Krzysztof Witkowski (kwitek)
• Lee Adams (leeaustinadams)
• Lorenzo Villani (lvillani)
• Magnar Sveen (magnars)
• Malyshev Artem (proofit404)
• Manuel Uberti (manuel-uberti)
• Marcin Antczak (marcinant)
• Marcus Majewski (hekto)
• Marian Schubert (maio)
• Mario Rodas (marsam)
• Mark Hellewell (markhellewell)
• Mark Karpov (mrkkrp)
• Matthew Curry (strawhatguy)
• Matthias Dahl (BinaryKhaos)
• Michael Pankov (mkpankov)
• Michael Alan Dorman (mdorman)
• Miro Bezjak (mbezjak)
• Mitch Tishmack (mitchty)
• Moritz Bunkus (mbunkus)
• Omair Majid (omajid)
• Per Nordlöw (nordlow)
• Peter Eisentraut (petere)
• Philipp Stephani (phst)
• Peter Vasil (ptrv)
• Robert Dallas Gray (rdallasgray)
• Robert O’Connor (robbyoconnor)
• Robert Zaremba (robert-zaremba)
• Saša Jovanić (Simplify)
• Sean Gillespie (swgillespie)
• Sean Salmon (phatcabbage)
• Sebastian Beyer (sebastianbeyer)
• Sebastian Wiesner (lunaryorn, founder, maintainer, owner)
• Sergey Vinokurov (sergv)
• Stephen Lewis (stephenjlewis)
• Steve Purcell (purcell)
• Sven Keidel (svenkeidel)
• Sylvain Benner (syl20bnr)
• Sylvain Rousseau (thisirs)
• Syohei Yoshida (syohex)
• Ted Zlatanov (tzz)
• Tom Jakubowski (tomjakubowski)
• Tomoya Tanjo (tom-tan)
• Victor Deryagin (vderyagin)
• Vlatko Basic (vlatkoB)
• William Cummings (wcummings)
• William Xu (xwl)
• Yannick Roehlly (yannick1974)
• Yasuyuki Oka (yasuyk)
• Zhuo Yuan (yzprofile)
• Łukasz Jędrzejewski (jedrz)

For a complete list of all code contributors see the Contributor Graph or git shortlog --summary.

The Contributor Guide

The Contributor Guide explains how to contribute to Flycheck.

Contributor’s Guide

Thank you very much for your interest in contributing to Flycheck! We’d like to warmly welcome you in the Flycheck community, and hope that you enjoy your time with us!

There are many ways to contribute to Flycheck, and we appreciate all of them. We hope that this document helps you to contribute. If you have questions, please ask on our issue tracker or in our Gitter chatroom.

For a gentle start please take a look at all the things we need your help with and look for beginner-friendly tasks.

Please note that all contributors are expected to follow our Code of Conduct.

Bug reports

Bugs are a sad reality in software, but we strive to have as few as possible in Flycheck. Please liberally report any bugs you find. If you are not sure whether something is a bug or not, please report anyway.

If you have the chance and time please search existing issues, as it’s possible that someone else already reported your issue. Of course, this doesn’t always work, and sometimes it’s very hard to know what to search for, so this is absolutely optional. We definitely don’t mind duplicates, please report liberally.

To open an issue simply fill out the issue form. To help us fix the issue, include as much information as possible. When in doubt, better include too much than too little. Here’s a list of facts that are important:

• What you did, and what you expected to happen instead
• Whether and how you were able to reproduce the issue in emacs -Q
• Your Flycheck setup from M-x flycheck-verify-setup
• Your operating system
• Your Emacs version from M-x emacs-version
• Your Flycheck version from M-x flycheck-version

Windows-only issues

As Flycheck does not support Windows officially we generally do not attempt to fix issues that only occur on Windows. We will move all Windows-only issues to the list of open Windows issues, and leave them to Windows users and developers.

We welcome anyone who wants to fix open Windows issues, and we will merge pull requests for improved Windows compatibility. If you know Windows and Emacs, please take a look at the list of open Windows issues and try to fix any of these.

Feature requests

To request a new feature please open a new issue through our issue form. A feature request needs to find a core developer or maintainer who adopts and implements it.

The Build system

Flycheck provides a Makefile with some convenient targets to compile and test Flycheck. The Makefile requires Cask, the Emacs Lisp dependency manager. Run make help to see a list of all available targets. Some common ones are:

• make init initialises the project by installing local Emacs Lisp dependencies.
• make check checks all Emacs Lisp sources. This target requires Emacs 25.
• make compile compiles Flycheck and its libraries to byte code.
• make format formats all Emacs Lisp sources.
• make specs runs all Buttercup specs for Flycheck. Set PATTERN to run only specs matching a specific regular expression, e.g. make PATTERN='^Mode Line' specs to run only tests for the mode line.
• make test runs all ERT unit tests for Flycheck. We are phasing ERT out in favour of Buttercup; no new ERT unit tests will be added and this target will eventually be removed.
• make integ runs all integration tests for Flycheck syntax checkers. These tests are very dependent on the checker programs and their versions; expect failures when running this target. Set SELECTOR to run only tests matching a specific ERT selector, e.g. make SELECTOR='(language haskell)' integ to run only integration tests for Haskell. make LANGUAGE=haskell integ is a shortcut for this.

Pull requests

Pull Requests are the primary mechanism to submit your own changes to Flycheck. Github provides great documentation about Pull Requests.

Please make your pull requests against the master branch.

Use make specs test to test your pull request locally. When making changes to syntax checkers of a specific language, it’s also a good idea to run make LANGUAGE=language integ and check whether the tests for the particular language still work. A successful make integ is by no means mandatory for pull requests, though, we will test your changes, too.

Important

To contribute to Flycheck you must sign our CLA (Contributor License Agreement). The CLA Assistant bot will automatically ask you to do this when you open a pull request, and let’s you sign the CLA through your Github account.

We require this process mostly to make you aware of the licensing implications of contributing to Flycheck and to obtain your explicit approval of our licenses for your contribution.

All pull requests are reviewed by a maintainer. Feel free to mention individual developers (e.g. @lunaryorn) to request a review from a specific person, or @flycheck/maintainers if you have general questions or if your pull request was waiting for review too long.

Additionally all pull requests go through automated tests on Travis CI which check code style, run unit tests, etc.

After the pull request was reviewed and if all tests passed maintainers will leave a LGTM comment at which point the pull request is ready for being merged.

Commit guidelines

The art of writing good commit messages is a wide subject. This model commit message illustrates our style:

Fix a foo bug

The first line is the summary, 50 characters or less.  Write in the
imperative and in present tense: “Fix bug”, not “fixed bug” or “fixes
bug”.

After the summary more paragraphs with detailed explanations may follow,
wrapped at 72 characters.  Separate multiple paragraphs by blank lines.

You may use simple formatting like *emphasis* or _underline_, but keep
it to a minimum.  Commit messages are not in Markdown :)

Commit messages may reference issues by number, like this: See GH-42.
Please use `GH-` to prefix issue numbers.  You may also close issues
like this: Fixes GH-42 and closes GH-42.

Git Commit and Magit provide Emacs mode for Git commit messages, which helps you to comply to these guidelines.

Writing documentation

Documentation improvements are very welcome. Flycheck’s manual is written in reStructuredText and built with Sphinx. The source of the manual resides in the doc/ directory.

You need Python 3.4 or newer to install Sphinx for Flycheck’s documentation. On OS X it is recommended that you use Homebrew to install the latest Python version with brew install python3. On Linux you should be able to obtain Python 3.4 from the package manager of your distribution.

With Python 3 installed change into the doc/ directory and run make init to install Sphinx and related tools required for Flycheck’s documentation. We recommend that you use virtualenv to avoid a global installation of Python modules. make init will warn you if you do not.

When editing documentation run make html-auto to view the results of your edits. This target runs a local webserver at http://localhost:8000 which serves the HTML documentation and watches the documentation sources for changes to rebuild automatically. When you finished your edits it is a good idea to run make linkcheck to verify all links in the documentation. Note that this target can take a while especially when run on a clean build.

Run make help to see a list of all available Make targets for the documentation.

Documentation pull requests work in the same way as other pull requests. To find documentation issues sort by the documentation label.

Issue management

We use Github labels for basic issue management:

• The red “bug” label denotes critical bugs in Flycheck that must be fixed urgently.
• Violet labels describe the area of Flycheck the issue belongs to.
• The green “beginner friendly” label denotes easy tasks for newcomers to the project.
• Orange labels denote blockers.
• Grey labels indicate resolutions to issues.

Out of tree contributions

There are many ways that you can contribute to Flycheck that go beyond this repository.

Answer questions in our Gitter channel or on StackExchange.

Participate in Flycheck discussions in other Emacs communities and help users with troubles.

Write extensions for Flycheck.

---

This contributing guide is heavily inspired by Rust’s excellent contributing information.

Maintainer’s Guide

Issue triage

Please label incoming tickets accordingly according to these rules:

• Add the “bug” label to things that you think must be fixed urgently. Please don’t use this label for bugs that do not severely impede Flycheck’s functionality.
• Add the “needs review” label to new bugs and pull requests that need to be reviewed.
• Add the “beginner friendly” label to really easy things. If you add this label please also add a comment that outlines a possible solution.
• Add “blocked” to bugs that need further comment or help from the reporter, and to pull requests that need to be improved.
• Add “windows only” for bugs that appear to only affect Windows operating systems.

If you’d like to review a bug or pull request please assign the corresponding ticket to you.

In issues for specific languages that Flycheck support please mention the corresponding language team if one exists.

Git workflow

Our Git workflow is simple:

• The master branch is always shippable.
• Every feature and every non-trivial change goes through a pull request.

GitHub calls this the “GitHub Flow” and has a very nice visual guide for this model.

Branch rules

Our workflow implies a couple of rules about which branches to push code to:

• Please commit new features, larger changes and refactorings and updates to documentation to separate branches and open a pull request for review and discussion.
• The master branch is protected. Only owners can push directly to it. Everyone else needs to open a pull request. Github requires maintainer approval and passing Travis CI tests before a pull request can be merged to master.

Important

When creating a new branch please use a descriptive name to communicate the purpose of the branch to other developers and maintainers. fix-bug-42 is not a great name, but 42-fix-void-function-error-in-error-list is.

Pull requests

All pull requests require approval of a maintainer.

To state your approval as a maintainer add a comment that contains LGTM. The LGTM.co will look for these comments and unlock the pull request once enough maintainers approved it. We require approvals from multiple maintainers, see .lgtm for the exact amount of approvals required to accept a pull request.

Important

LGTM.co does not require repeated approval after changes to the pull request. Hence you can “approve early”, i.e. approve before the pull request is polished.

And it’s absolutely fine to do so. If there are only minor changes left, if you trust the pull request author to address remaining issues, feel free to approve early, all the more if the pull request author is already a contributor. In this case they’ll be able to directly merge their own pull request after making changes to it which decreases the turn-around time for pull requests.

Review guidelines

Todo

Write pull request review guidelines

Merge guidelines

If a pull request was approved you may directly merge it. For smaller pull requests please “Squash and Merge” to keep a linear history, otherwise merge normally. What constitutes a “small” pull request is at your discretion. Apply common sense :)

You may also add the author of the pull request to the “Core developers” team to give them commit access to the Flycheck repository and ask them merge the pull request themselves. That’s a good way to gain new contributors.

Signatures for commits and tags

We sign all release tags as part of our Release process. Thus you need a GPG key pair for Git. Github provides a great guide which helps you to generate a key and to tell Git about your key. Please also add your key to your Github account.

We also recommend that you sign all your commits with your key. Again, Github provides a good guide to sign commits.

See also

Signing Your Work

For more information about signing commits and tags take a look at the section in the Git manual.

Tooling and Services

In addition to Github where we host code and do code reviews we use a bit of extra tooling and some 3rd party services for Flycheck:

• ReadTheDocs hosts http://www.flycheck.org and automatically rebuilds it on every change. It works mostly automatically and requires little configuration.
• Travis CI runs our tests after every push and for every pull request. It’s configured through .travis.yml.
• LGTM handles the pull request approval process through LGTM comments. It’s configured through .lgtm, the list of maintainers that may approve pull requests is in the MAINTAINERS file.
• CLA assistant checks signatures to our CLA and allows contributors to sign the CLA through their Github account.

All maintainers have administrative access to these services so in case of an issue just contact them.

Maintenance scripts

Administrative processes are tedious and time-consuming, so we try to automate as much as possible. The maint/ directory contains many scripts for this purpose. make -C maint/ help provides an overview over all administrative tasks.

Most of these scripts require Python 3.5 and additional Python libraries. On OS X it is recommended that you use Homebrew to install the latest Python version with brew install python3. On Linux you should be able to obtain Python 3.5 from the package manager of your distribution.

To install all required libraries run make -C maint init. We recommend that you use virtualenv to avoid a global installation of Python modules. make init will warn you if you do not.

Versioning and releases

We use a single continuously increasing version number for Flycheck. Breaking changes may occur at any point.

Please feel free to make a release whenever you think it’s appropriate. It’s generally a good idea to release when

• you fixed an important bug that affects many users,
• there are a couple of new syntax checkers available,
• there’s a major new feature in master,
• etc.

In doubt just make a release. We aim to release early and frequently. If anything breaks anything we can just publish another release afterwards.

Release process

First, check that

1. you are on master,
2. your working directory is clean, i.e. has no uncommitted changes or untracked files,
3. all commits are pushed,
4. and Travis CI passes for the latest commit on master.

If all is good a new release is a simple as

$ make -C maint release

This runs the release script in maint/release.py. If any of the above requirements isn’t met the release script will signal an error and abort.

The release script bumps the version number, commits and tags a new release, and pushes it to Github.

Note

The tag is signed; you must configure Git for signing commits and tags before you make a release the first time. After pushing the new release to Github, the script bumps the version number again, to the next snapshot, and commits the changes again.

Once the script is completed please

1. Edit the release information on Github and add a short summary about the release. Don’t forget to add a link to the complete changelog and upload the package TAR file.
2. Enable the new release on the ReadTheDocs versions dashboard.
3. Announce the new release in our Gitter channel, on emacs_flycheck Twitter and wherever else you see fit.

New maintainers

To propose a new maintainer open a pull request that adds the user to MAINTAINERS and doc/community/people.rst. The pull request is subject to the same rules as all other pull requests. Notably it goes through the same approval process.

Once merged please also

• add the new maintainer to the Maintainers team of the Github organisation. This does not award additional privileges, it’s just to support @flycheck/maintainers mentions for the sake of convenience,
• invite the new maintainer to the internal Maintainers channel on Gitter,
• and announce the new maintainer on Flycheck’s Twitter account.

Indices and Tables

• Supported Languages
• Glossary
• Changes
• Index
• Search Page

Supported Languages

This document lists all programming and markup languages which Flycheck supports.

Note

Extensions may provide support for additional languages or add deeper integration with existing languages.

Take a look at the list of extensions to see what the community can offer to you.

Each language has one or more syntax checkers whose names follow a convention of language-tool. All syntax checkers are listed in the order they would be applied to a buffer, with all available options. For more information about a syntax checker open Emacs and use flycheck-describe-checker to view the docstring of the syntax checker. Likewise, you may use describe-variable to read the complete docstring of any option.

Ada

ada-gnat

Check ADA syntax and types with GNAT.

flycheck-gnat-args

A list of additional options.

flycheck-gnat-include-path

A list of include directories. Relative paths are relative to the path of the buffer being checked.

flycheck-gnat-language-standard

The language standard to use as string.

flycheck-gnat-warnings

A list of additional warnings to enable. Each item is the name of a warning category to enable.

AsciiDoc

asciidoc

Check AsciiDoc with the standard AsciiDoc processor.

C/C++

Flycheck checks C and C++ with either c/c++-clang or c/c++-gcc, and then with c/c++-cppcheck.

c/c++-clang

c/c++-gcc

Check C/C++ for syntax and type errors with Clang or GCC respectively.

Note

c/c++-gcc requires GCC 4.8 or newer.

flycheck-clang-args

flycheck-gcc-args

A list of additional arguments for c/c++-clang and c/c++-gcc respectively.

flycheck-clang-blocks

Whether to enable blocks in c/c++-clang.

flycheck-clang-definitions

flycheck-gcc-definitions

A list of additional preprocessor definitions for c/c++-clang and c/c++-gcc respectively.

flycheck-clang-include-path

flycheck-gcc-include-path

A list of include directories for c/c++-clang and c/c++-gcc respectively, relative to the file being checked.

flycheck-clang-includes

flycheck-gcc-includes

A list of additional include files for c/c++-clang and c/c++-gcc respectively, relative to the file being checked.

flycheck-clang-language-standard

flycheck-gcc-language-standard

The language standard to use in c/c++-clang and c/c++-gcc respectively as string, via the -std option.

flycheck-clang-ms-extensions

Whether to enable Microsoft extensions to C/C++ in c/c++-clang.

flycheck-clang-no-exceptions

flycheck-gcc-no-exceptions

Whether to disable exceptions in c/c++-clang and c/c++-gcc respectively.

flycheck-clang-no-rtti

flycheck-gcc-no-rtti

Whether to disable RTTI in c/c++-clang and c/c++-gcc respectively, via -fno-rtti.

flycheck-clang-standard-library

The name of the standard library to use for c/c++-clang, as string.

flycheck-gcc-openmp

Whether to enable OpenMP in c/c++-gcc.

flycheck-clang-pedantic

flycheck-gcc-pedantic

Whether to warn about language extensions in c/c++-clang and c/c++-gcc respectively.

flycheck-clang-pedantic-errors

flycheck-gcc-pedantic-errors

Whether to error on language extensions in c/c++-clang and c/c++-gcc respectively.

flycheck-clang-warnings

flycheck-gcc-warnings

A list of additional warnings to enable in c/c++-clang and c/c++-gcc respectively. Each item is the name of a warning or warning category for -W.

c/c++-cppcheck

Check C/C++ for semantic and stylistic issues with cppcheck.

flycheck-cppcheck-checks

A list of enabled checks. Each item is the name of a check for the --enable option.

flycheck-cppcheck-inconclusive

Whether to enable inconclusive checks. These checks may yield more false positives than normal checks.

Note

This option requires cppcheck 1.54 or newer.

flycheck-cppcheck-include-path

A list of include directories. Relative paths are relative to the file being checked.

flycheck-cppcheck-standards

The C, C++ and/or POSIX standards to use via one or more --std= arguments.

flycheck-cppcheck-suppressions

The cppcheck suppressions list to use via one or more --suppress= arguments.

CFEngine

cfengine

Check syntax with CFEngine.

Chef

chef-foodcritic

Check style in Chef recipes with foodcritic.

flycheck-foodcritic-tags

A list of tags to select.

Coffeescript

Flycheck checks Coffeescript syntax with coffee and then lints with coffee-coffeelint.

coffee

Check syntax with the Coffeescript compiler.

coffee-coffeelint

Lint with Coffeelint.

flycheck-coffeelintrc

Configuration file for this syntax checker. See flycheck-config-files.

Coq

coq

Check and proof with the standard Coq compiler.

CSS

css-csslint

Check syntax and style with CSSLint.

D

d-dmd

Check syntax and types with (DMD).

Note

This syntax checker requires DMD 2.066 or newer.

flycheck-dmd-include-path

A list of include directories.

flycheck-dmd-args

A list of additional arguments.

See also

flycheck-d-unittest

Flycheck extension which provides a syntax checker to run D unittests on the fly and report the results with Flycheck.

Emacs Lisp

Flycheck checks Emacs Lisp with emacs-lisp and then with emacs-lisp-checkdoc.

emacs-lisp

Check syntax with the built-in byte compiler.

flycheck-emacs-lisp-load-path

The load path as list of strings. Relative directories are expanded against the default-directory of the buffer being checked.

flycheck-emacs-lisp-initialize-packages

Whether to initialize Emacs’ package manager with package-initialize before checking the buffer. If set to auto (the default), only initialize the package managers when checking files under user-emacs-directory.

flycheck-emacs-lisp-package-user-dir

The package directory as string. Has no effect if flycheck-emacs-lisp-initialize-packages is nil.

emacs-lisp-checkdoc

Check Emacs Lisp documentation conventions with checkdoc.

See also

Documentation Tips(elisp)

Information about documentation conventions for Emacs Lisp.

purcell/flycheck-package

Flycheck extension which adds a syntax checker to check for violation of Emacs Lisp library headers and packaging conventions.

Library Headers(elisp)

Information about library headers for Emacs Lisp files.

Erlang

erlang

Check Erlang with the standard Erlang compiler.

flycheck-erlang-include-path

A list of include directories.

flycheck-erlang-library-path

A list of library directories.

ERuby

eruby-erubis

Check ERuby with erubis.

Fortran

fortran-gfortran

Check Fortran syntax and type with GFortran.

flycheck-gfortran-args

A list of additional arguments.

flycheck-gfortran-include-path

A list of include directories. Relative paths are relative to the file being checked.

flycheck-gfortran-language-standard

The language standard to use via the -std option.

flycheck-gfortran-layout

The source code layout to use. Set to free or fixed for free or fixed layout respectively, or nil (the default) to let GFortran automatically determine the layout.

flycheck-gfortran-warnings

A list of warnings enabled via the -W option.

Go

Flycheck checks Go with the following checkers:

1. go-gofmt
2. go-golint
3. go-vet
4. go-build or go-test
5. go-errcheck
6. go-unconvert

go-gofmt

Check Go syntax with gofmt.

go-golint

Check Go code style with Golint.

go-vet

Check Go for suspicious code with vet.

flycheck-go-vet-print-functions

A list of print-like functions to check calls for format string problems.

flycheck-go-vet-shadow

Whether to check for shadowed variables, in Go 1.6 or newer.

go-build

Check syntax and type with the Go compiler.

Note

This syntax checker requires Go 1.6 or newer.

flycheck-go-build-install-deps

Whether to install dependencies while checking with go-build or go-test

flycheck-go-build-tags

A list of build tags.

go-test

Check syntax and types of Go tests with the Go compiler.

Note

This syntax checker requires Go 1.6 or newer.

flycheck-go-build-install-deps

See flycheck-go-build-install-deps.

go-errcheck

Check for unhandled error returns in Go with errcheck.

Note

This syntax checker requires errcheck build from commit 8515d34 (Aug 28th, 2015) or newer.

go-unconvert

Check for unnecessary type conversions with unconvert.

Groovy

groovy

Check syntax using the Groovy compiler.

Haml

haml

Check syntax with the Haml compiler.

Handlebars

handlebars

Check syntax with the Handlebars compiler.

Haskell

Flycheck checks Haskell with haskell-stack-ghc (in Stack projects) or haskell-ghc, and then with haskell-hlint.

See also

flycheck-haskell

Flycheck extension to configure Flycheck’s Haskell checkers from the metadata, with support for Cabal sandboxes.

flycheck-hdevtools

Flycheck extension which adds an alternative syntax checker for GHC using hdevtools.

haskell-stack-ghc

haskell-ghc

Check syntax and type GHC. In Stack projects invoke GHC through Stack to bring package dependencies from Stack in.

flycheck-ghc-args

A list of additional arguments.

flycheck-ghc-no-user-package-database

Whether to disable the user package database (only for haskell-ghc).

flycheck-ghc-stack-use-nix

Whether to enable Nix support for Stack (only for haskell-stack-ghc).

flycheck-ghc-package-databases

A list of additional package databases for GHC (only for haskell-ghc). Each item points to a directory containing a package directory, via -package-db.

flycheck-ghc-search-path

A list of module directories, via -i.

flycheck-ghc-language-extensions

A list of language extensions, via -X.

haskell-hlint

Lint with hlint.

flycheck-hlint-args

A list of additional arguments.

flycheck-hlint-language-extensions

A list of language extensions to enable.

flycheck-hlint-ignore-rules

A list of rules to ignore.

flycheck-hlint-hint-packages

A list of additional hint packages to include.

flycheck-hlintrc

Configuration file for this syntax checker. See flycheck-config-files.

HTML

html-tidy

Check HTML syntax and style with Tidy HTML5.

flycheck-tidyrc

Configuration file for this syntax checker. See flycheck-config-files.

Jade

jade

Check syntax using the Jade compiler.

Javascript

Flycheck checks Javascript with one of javascript-eslint, javascript-jshint or javascript-gjslint, and then with javascript-jscs.

Alternatively javascript-standard is used instead all of the former ones.

javascript-eslint

Check syntax and lint with ESLint.

flycheck-eslint-rules-directories

A list of directories with custom rules.

flycheck-eslintrc

Configuration file for this syntax checker. See flycheck-config-files.

javascript-jshint

Check syntax and lint with JSHint.

flycheck-jshint-extract-javascript

Whether to extract Javascript from HTML before linting.

flycheck-jshintrc

Configuration file for this syntax checker. See flycheck-config-files.

javascript-gjslint

Lint with Closure Linter.

flycheck-gjslintrc

Configuration file for this syntax checker. See flycheck-config-files.

javascript-jscs

Check code style with JSCS.

flycheck-jscsrc

Configuration file for this syntax checker. See flycheck-config-files.

javascript-standard

Check syntax and code style with Standard or Semistandard.

JSON

Flycheck checks JSON with json-jsonlint or json-python-json.

json-jsonlint

Check JSON with jsonlint.

json-python-json

Check JSON with Python’s built-in json module.

Less

less

Check syntax with the Less compiler.

Note

This syntax checker requires lessc 1.4 or newer.

Lua

Flycheck checks Lua with lua-luacheck, falling back to lua.

lua-luacheck

Check syntax and lint with Luacheck.

flycheck-luacheckrc

Configuration file for this syntax checker. See flycheck-config-files.

lua

Check syntax with the Lua compiler.

Markdown

markdown-mdl

Check Markdown with markdownlint.

flycheck-markdown-mdl-rules

A list of enabled rules.

flycheck-markdown-mdl-tags

A list of enabled rule tags.

flycheck-markdown-mdl-style

Configuration file for this syntax checker. See flycheck-config-files.

Perl

Flycheck checks Perl with perl and perl-perlcritic.

perl

Check syntax with the Perl interpreter.

flycheck-perl-include-path

A list of include directories, relative to the file being checked.

perl-perlcritic

Lint and check style with Perl::Critic.

flycheck-perlcritic-severity

The severity level as integer for the --severity.

flycheck-perlcriticrc

Configuration file for this syntax checker. See flycheck-config-files.

PHP

Flycheck checks PHP with php, php-phpmd and php-phpcs.

php

Check syntax with PHP CLI

php-phpmd

Lint with PHP Mess Detector.

flycheck-phpmd-rulesets

A list of rule sets. Each item is either the name of a default rule set, or the path to a custom rule set file.

php-phpcs

Check style with PHP Code Sniffer.

Note

This syntax checker requires PHP Code Sniffer 2.6 or newer.

flycheck-phpcs-standard

The coding standard, either as name of a built-in standard, or as path to a standard specification.

Processing

processing

Check syntax using the Processing compiler.

Puppet

Flycheck checks Puppet with puppet-parser and lints with puppet-lint.

puppet-parser

Check syntax with the Puppet compiler.

puppet-lint

Link with Puppet Lint.

flycheck-puppet-lint-disabled-checks

A list of checks to disable.

flycheck-puppet-lint-rc

Configuration file for this syntax checker. See flycheck-config-files.

Python

Flycheck checks Python with python-flake8 or python-pylint, and falls back to python-pycompile if neither of those is available.

See also

flycheck-pyflakes

Flycheck extension which adds a syntax checker using Pyflakes.

python-flake8

Check syntax and lint with flake8.

Note

This syntax checker requires flake8 2.0 or newer.

flycheck-flake8-error-level-alist

An alist mapping Flake8 error IDs to Flycheck error levels.

flycheck-flake8-maximum-complexity

The maximum McCabe complexity allowed for methods.

flycheck-flake8-maximum-line-length

The maximum length of lines.

flycheck-flake8rc

Configuration file for this syntax checker. See flycheck-config-files.

python-pylint

Check syntax and lint with Pylint.

Note

This syntax checker requires Pylint 1.0 or newer.

flycheck-pylint-use-symbolic-id

Whether to report symbolic (e.g. no-name-in-module) or numeric (e.g. E0611) message identifiers.

flycheck-pylintrc

Configuration file for this syntax checker. See flycheck-config-files.

python-pycompile

Check syntax with Python’s byte compiler (see py_compile).

R

r-lintr

Check syntax and lint with lintr.

flycheck-lintr-caching

Whether to enable caching in lintr. On by default; it is not recommended to disable caching unless it causes actual problems.

flycheck-lintr-linters

Linters to use as a string with an R expression which selects the linters to use.

Racket

racket

Check syntax with raco expand from the compiler-lib package.

Note

This syntax checker needs the compiler-lib package.

RPM Spec

rpm-rpmlint

Lint with rpmlint.

reStructuredText

Flycheck checks reStructuredText with rst-sphinx in Sphinx projects and with rst otherwise.

rst-sphinx

Check documents with Sphinx.

Note

This syntax checker requires Sphinx 1.2 or newer.

flycheck-sphinx-warn-on-missing-references

Whether to emit warnings for all missing references.

rst

Check documents with docutils.

Ruby

Flycheck checks Ruby with ruby-rubocop and ruby-rubylint, falling back to ruby or ruby-jruby for basic syntax checking if those are not available.

ruby-rubocop

Check syntax and lint with RuboCop.

Note

This syntax checker requires Rubocop 0.34 or newer.

flycheck-rubocop-lint-only

Whether to suppress warnings about style issues, via the --lint option.

flycheck-rubocoprc

Configuration file for this syntax checker. See flycheck-config-files.

ruby-rubylint

Check syntax and lint with ruby-lint.

Note

This syntax checker requires ruby-lint 2.0.2 or newer.

flycheck-rubylintrc

Configuration file for this syntax checker. See flycheck-config-files.

ruby

Check syntax with the Ruby interpreter.

ruby-jruby

Check syntax with the JRuby interpreter.

Rust

Flycheck checks Rust with rust-cargo in Cargo projects, or rust otherwise.

rust-cargo

rust

Check syntax and types with the Rust compiler. In a Cargo project the compiler is invoked through cargo rustc to take Cargo dependencies into account.

Note

These syntax checkers require Rust 1.7 or newer.

See also

flycheck-rust

Flycheck extension to configure Rust syntax checkers according to the current Cargo project.

flycheck-rust-args

A list of additional arguments.

flycheck-rust-check-tests

Whether to check test code in Rust.

flycheck-rust-crate-root

A path to the crate root for the current buffer, or nil if the current buffer is a crate by itself.

rust-cargo ignores this option as the crate root is given by Cargo.

flycheck-rust-crate-type

The type of the crate to check, as string for the --crate-type option.

flycheck-rust-binary-name

The name of the binary to pass to cargo rustc --bin, as a string.

Only required when flycheck-rust-crate-type is bin and the crate has multiple targets.

flycheck-rust-library-path

A list of additional library directories. Relative paths are relative to the buffer being checked.

Sass

sass

Check syntax with the Sass compiler.

flycheck-sass-compass

Whether to enable the Compass CSS framework via --compass.

Scala

Flycheck checks Scala with scala and scala-scalastyle.

scala

Check syntax and types with the Scala compiler.

Note

This syntax checker is fairly primitive. For a better Scala experience we recommend Ensime.

scala-scalastyle

Check style with Scalastyle.

flycheck-scalastylerc

Configuration file for this syntax checker. See flycheck-config-files.

Important

A configuration file is mandatory for this syntax checker. If flycheck-scalastylerc is not set or the configuration file not found this syntax checker will not be applied.

Scheme

Flycheck checks CHICKEN Scheme files with csc.

scheme-chicken

Check syntax with csc, the CHICKEN Scheme compiler.

Important

Geiser must be installed and active for this checker to work.

SCSS

Flycheck checks SCSS with scss-lint, falling back to scss.

scss-lint

Check syntax and lint with SCSS-Lint.

Note

This syntax checker requires SCSS-Lint 0.43.2 or newer.

flycheck-scss-lintrc

Configuration file for this syntax checker. See flycheck-config-files.

scss

Check syntax with the SCSS compiler.

flycheck-scss-compass

Whether to enable the Compass CSS framework with --compass.

Shell scripting languages

Flycheck checks various shell scripting languages:

• Bash with sh-bash and sh-shellcheck
• POSIX shell (i.e. /bin/sh) with sh-posix-dash or sh-posix-bash
• Zsh with sh-zsh

sh-bash

Check Bash syntax.

sh-posix-dash

Check POSIX shell syntax with Dash.

sh-posix-bash

Check POSIX shell syntax with Bash.

sh-zsh

Check Zsh syntax.

sh-shellcheck

Lint Bash and POSIX shell with ShellCheck.

flycheck-shellcheck-excluded-warnings

A list of excluded warnings.

Slim

slim

Check Slim using the Slim compiler.

slim-lint

Check Slim best practices using the slim-lint linter.

SQL

sql-sqlint

Check SQL syntax with Sqlint.

TeX/LaTeX

Flycheck checks TeX and LaTeX with either tex-chktex or tex-lacheck.

tex-chktex

Check style with ChkTeX.

flycheck-chktexrc

Configuration file for this syntax checker. See flycheck-config-files.

tex-lacheck

Check style with Lacheck.

Texinfo

texinfo

Check syntax with makeinfo from Texinfo.

TypeScript

typescript-tslint

Check syntax and style with TSLint.

flycheck-typescript-tslint-config

Configuration file for this syntax checker. See flycheck-config-files.

flycheck-typescript-tslint-rulesdir

Additional rules directory, for user created rules.

Verilog

verilog-verilator

Check syntax with Verilator.

flycheck-verilator-include-path

A list of include directories. Relative paths are relative to the file being checked.

XML

Flycheck checks XML with xml-xmlstarlet or xml-xmllint.

xml-xmlstarlet

Check syntax with XMLStarlet.

xml-xmllint

Check syntax with xmllint from Libxml2.

YAML

Flycheck checks YAML with yaml-jsyaml or yaml-ruby.

yaml-jsyaml

Check syntax with js-yaml.

yaml-ruby

Check syntax with Ruby’s YAML parser.

Glossary

The glossary explains most of the special terms we use in this documentation. some of these are originally explained in the Emacs manual or the Emacs Lisp reference, but we reproduce them here for convenience.

init file

user init file

Your main Emacs configuration file. It’s typically located in your user emacs directory at $HOME/.emacs.d/init.el. Emacs also looks at $HOME/.emacs, but this location is not recommended anymore. To find out the actual path to your init file of your Emacs session inspect the value of the variable user-init-file with C-h v user-init-file. You can visit it directly with M-: (find-file user-init-file).

See also

Init File(emacs)

More information about the init file.

Init File(elisp)

Programming interface for the init file.

user emacs directory

The directory for all Emacs related files of the current user, at ~/.emacs.d/. Many Emacs packages create data files in this directory, and it holds the recommended location for the init file at ~/.emacs.d/init.el.

registered syntax checker

A syntax checker in flycheck-checkers. Flycheck will only use these syntax checkers when checking buffers automatically.

Changes

29 (Aug 28, 2016)

• Breaking changes
  • Change flycheck-eslint-rulesdir (string) to flycheck-eslint-rules-directories (list of strings) [GH-1016]
  • Require rust 1.7 or newer for rust and rust-cargo [GH-1036]
• New syntax checkers:
  • Slim with slim-lint [GH-1013]
  • CHICKEN Scheme with csc [GH-987]
• New features:
  • Add :working-directory option to flycheck-define-command-checker [GH-973] [GH-1012]
  • flycheck-go-build-install-deps turns on dependency installation for go test as well as go build [GH-1003]
• Improvements:
  • Add default directory for haskell-stack-ghc and haskell-ghc checkers [GH-1007]
  • rust and rust-cargo checkers now support the new error format of rust 1.12 [GH-1016]
  • flycheck-verify-checker and flycheck-verify-setup now include information about configuration files of syntax checkers [GH-1021] [GH-1038]

28 (Jun 05, 2016)

• Breaking changes:
  • Rename luacheck to lua-luacheck to comply with our naming conventions
  • Remove flycheck-cppcheck-language-standard in favour of flycheck-cppcheck-standards which is a list of standards [GH-960]
• New features:
  • Add option to set binary name for rust-cargo [GH-958]
  • Add flycheck-cppcheck-standards to pass multiple code standards to cppcheck [GH-960]
  • Add flycheck-cppcheck-suppressions to suppress warnings for cppcheck [GH-960]
• Improvements:
  • Check Racket syntax in Geiser Mode [GH-979]
• Bug fixes
  • Do not signal errors when tslint reports no output [GH-981]
  • Do not generate invalid temporary filenames on Windows [GH-983]

27 (May 08, 2016)

• Breaking changes
  • Require PHP Code Sniffer 2.6 or newer for php-phpcs [GH-921]
• New syntax checkers:
  • Go with go-unconvert [GH-905]
  • Markdown with mdl [GH-839] [GH-916]
  • TypeScript with tslint [GH-947] [GH-949]
• Improvements:
  • Pass checkdoc settings from Emacs to emacs-lisp-checkdoc [GH-741] [GH-937]
• Bug fixes:
  • Fix parsing of syntax errors in triple-quoted strings for python-pycompile [GH-948]
  • Correctly handle rules based on the current file name in php-phpcs [GH-921]

26 (Apr 27, 2016)

Flycheck now has a Code of Conduct which defines the acceptable behaviour and the moderation guidelines for the Flycheck community. [GH-819]

Flycheck also provides a Gitter channel now for questions and discussions about development. [GH-820]

The native Texinfo manual is again replaced with a Sphinx based documentation. We hope that this change makes the manual easier to edit and to maintain and more welcoming for new contributors. The downside is that we can not longer include a Info manual in Flycheck’s MELPA packages.

From this release onward Flycheck will use a single continuously increasing version number. Breaking changes may occur at any point.

• Breaking changes:
  • Remove flycheck-copy-messages-as-kill, obsolete since Flycheck 0.22
  • Remove flycheck-perlcritic-verbosity, obsolete since Flycheck 0.22
  • Replace flycheck-completion-system with flycheck-completing-read-function [GH-870]
  • JSON syntax checkers now require json-mode and do not check in Javascript Mode anymore
  • Prefer eslint over jshint for Javascript
  • Obsolete flycheck-info in favour of the new flycheck-manual command
• New syntax checkers:
  • Processing [GH-793] [GH-812]
  • Racket [GH-799] [GH-873]
• New features:
  • Add flycheck-puppet-lint-rc to customise the location of the puppetlint configuration file [GH-846]
  • Add flycheck-puppet-lint-disabled-checks to disable specific checks of puppetlint [GH-824]
  • New library flycheck-buttercup to support writing Buttercup specs for Flycheck
  • Add flycheck-perlcriticrc to set a configuration file for Perl::Critic [GH-851]
  • Add flycheck-jshint-extract-javascript to extract Javascript from HTML [GH-825]
  • Add flycheck-cppcheck-language-standard to set the language standard for cppcheck [GH-862]
  • Add flycheck-mode-line-prefix to customise the prefix of Flycheck’s mode line lighter [GH-879] [GH-880]
  • Add flycheck-go-vet-shadow to check for shadowed variables with go vet [GH-765] [GH-897]
  • Add flycheck-ghc-stack-use-nix to enable Nix support for Stack GHC [GH-913]
• Improvements:
  • Map error IDs from flake8-pep257 to Flycheck error levels
  • Explicitly display errors at point with C-c ! h [GH-834]
  • Merge message and checker columns in the error list to remove redundant ellipsis [GH-828]
  • Indicate disabled checkers in verification buffers [GH-749]
  • Do not enable Flycheck Mode in fundamental-mode buffers [GH-883]
  • Write go test output to a temporary files [GH-887]
  • Check whether lintr is actually installed [GH-911]
• Bug fixes:
  • Fix folding of C/C++ errors from included files [GH-783]
  • Fix verification of SCSS-Lint checkstyle reporter
  • Don’t fall back to rust if rust-cargo should be used [GH-817]
  • Don’t change current buffer when closing the error message buffer [GH-648]
  • Never display error message buffer in current window [GH-822]
  • Work around a caching issue in Rubocop [GH-844]
  • Fix checkdoc failure with some Emacs Lisp syntax [GH-833] [GH-845] [GH-898]
  • Correctly parse Haskell module name with exports right after the module name [GH-848]
  • Don’t hang when sending buffers to node.js processes on Windows [GH-794][GH-850]
  • Parse suggestions from hlint [GH-874]
  • Go errcheck handles multiple $GOPATH entries correctly now [GH-580][GH-906]
  • Properly handle Go build failing in a directory with multiple packages [GH-676] [GH-904]
  • Make cppcheck recognise C++ header files [GH-909]
  • Don’t run phpcs on empty buffers [GH-907]

Licensing

Flycheck 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.

Flycheck 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.

See GNU General Public License 3 for a copy of the GNU General Public License.

You may copy, distribute and/or modify the Flycheck documentation under the terms of the Creative Commons Attribution-ShareAlike 4.0 International Public License. See Creative Commons Attribution-ShareAlike 4.0 International for a copy of the license.

Permission is granted to copy, distribute and/or modify the Flycheck logo under the terms of the Creative Commons Attribution-ShareAlike 4.0 International Public License. See Creative Commons Attribution-ShareAlike 4.0 International for a copy of the license.

Flycheck licenses

GNU General Public License 3

                    GNU GENERAL PUBLIC LICENSE
                       Version 3, 29 June 2007

 Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
 Everyone is permitted to copy and distribute verbatim copies
 of this license document, but changing it is not allowed.

                            Preamble

  The GNU General Public License is a free, copyleft license for
software and other kinds of works.

  The licenses for most software and other practical works are designed
to take away your freedom to share and change the works.  By contrast,
the GNU General Public License is intended to guarantee your freedom to
share and change all versions of a program--to make sure it remains free
software for all its users.  We, the Free Software Foundation, use the
GNU General Public License for most of our software; it applies also to
any other work released this way by its authors.  You can apply it to
your programs, too.

  When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
them if you wish), that you receive source code or can get it if you
want it, that you can change the software or use pieces of it in new
free programs, and that you know you can do these things.

  To protect your rights, we need to prevent others from denying you
these rights or asking you to surrender the rights.  Therefore, you have
certain responsibilities if you distribute copies of the software, or if
you modify it: responsibilities to respect the freedom of others.

  For example, if you distribute copies of such a program, whether
gratis or for a fee, you must pass on to the recipients the same
freedoms that you received.  You must make sure that they, too, receive
or can get the source code.  And you must show them these terms so they
know their rights.

  Developers that use the GNU GPL protect your rights with two steps:
(1) assert copyright on the software, and (2) offer you this License
giving you legal permission to copy, distribute and/or modify it.

  For the developers' and authors' protection, the GPL clearly explains
that there is no warranty for this free software.  For both users' and
authors' sake, the GPL requires that modified versions be marked as
changed, so that their problems will not be attributed erroneously to
authors of previous versions.

  Some devices are designed to deny users access to install or run
modified versions of the software inside them, although the manufacturer
can do so.  This is fundamentally incompatible with the aim of
protecting users' freedom to change the software.  The systematic
pattern of such abuse occurs in the area of products for individuals to
use, which is precisely where it is most unacceptable.  Therefore, we
have designed this version of the GPL to prohibit the practice for those
products.  If such problems arise substantially in other domains, we
stand ready to extend this provision to those domains in future versions
of the GPL, as needed to protect the freedom of users.

  Finally, every program is threatened constantly by software patents.
States should not allow patents to restrict development and use of
software on general-purpose computers, but in those that do, we wish to
avoid the special danger that patents applied to a free program could
make it effectively proprietary.  To prevent this, the GPL assures that
patents cannot be used to render the program non-free.

  The precise terms and conditions for copying, distribution and
modification follow.

                       TERMS AND CONDITIONS

  0. Definitions.

  "This License" refers to version 3 of the GNU General Public License.

  "Copyright" also means copyright-like laws that apply to other kinds of
works, such as semiconductor masks.

  "The Program" refers to any copyrightable work licensed under this
License.  Each licensee is addressed as "you".  "Licensees" and
"recipients" may be individuals or organizations.

  To "modify" a work means to copy from or adapt all or part of the work
in a fashion requiring copyright permission, other than the making of an
exact copy.  The resulting work is called a "modified version" of the
earlier work or a work "based on" the earlier work.

  A "covered work" means either the unmodified Program or a work based
on the Program.

  To "propagate" a work means to do anything with it that, without
permission, would make you directly or secondarily liable for
infringement under applicable copyright law, except executing it on a
computer or modifying a private copy.  Propagation includes copying,
distribution (with or without modification), making available to the
public, and in some countries other activities as well.

  To "convey" a work means any kind of propagation that enables other
parties to make or receive copies.  Mere interaction with a user through
a computer network, with no transfer of a copy, is not conveying.

  An interactive user interface displays "Appropriate Legal Notices"
to the extent that it includes a convenient and prominently visible
feature that (1) displays an appropriate copyright notice, and (2)
tells the user that there is no warranty for the work (except to the
extent that warranties are provided), that licensees may convey the
work under this License, and how to view a copy of this License.  If
the interface presents a list of user commands or options, such as a
menu, a prominent item in the list meets this criterion.

  1. Source Code.

  The "source code" for a work means the preferred form of the work
for making modifications to it.  "Object code" means any non-source
form of a work.

  A "Standard Interface" means an interface that either is an official
standard defined by a recognized standards body, or, in the case of
interfaces specified for a particular programming language, one that
is widely used among developers working in that language.

  The "System Libraries" of an executable work include anything, other
than the work as a whole, that (a) is included in the normal form of
packaging a Major Component, but which is not part of that Major
Component, and (b) serves only to enable use of the work with that
Major Component, or to implement a Standard Interface for which an
implementation is available to the public in source code form.  A
"Major Component", in this context, means a major essential component
(kernel, window system, and so on) of the specific operating system
(if any) on which the executable work runs, or a compiler used to
produce the work, or an object code interpreter used to run it.

  The "Corresponding Source" for a work in object code form means all
the source code needed to generate, install, and (for an executable
work) run the object code and to modify the work, including scripts to
control those activities.  However, it does not include the work's
System Libraries, or general-purpose tools or generally available free
programs which are used unmodified in performing those activities but
which are not part of the work.  For example, Corresponding Source
includes interface definition files associated with source files for
the work, and the source code for shared libraries and dynamically
linked subprograms that the work is specifically designed to require,
such as by intimate data communication or control flow between those
subprograms and other parts of the work.

  The Corresponding Source need not include anything that users
can regenerate automatically from other parts of the Corresponding
Source.

  The Corresponding Source for a work in source code form is that
same work.

  2. Basic Permissions.

  All rights granted under this License are granted for the term of
copyright on the Program, and are irrevocable provided the stated
conditions are met.  This License explicitly affirms your unlimited
permission to run the unmodified Program.  The output from running a
covered work is covered by this License only if the output, given its
content, constitutes a covered work.  This License acknowledges your
rights of fair use or other equivalent, as provided by copyright law.

  You may make, run and propagate covered works that you do not
convey, without conditions so long as your license otherwise remains
in force.  You may convey covered works to others for the sole purpose
of having them make modifications exclusively for you, or provide you
with facilities for running those works, provided that you comply with
the terms of this License in conveying all material for which you do
not control copyright.  Those thus making or running the covered works
for you must do so exclusively on your behalf, under your direction
and control, on terms that prohibit them from making any copies of
your copyrighted material outside their relationship with you.

  Conveying under any other circumstances is permitted solely under
the conditions stated below.  Sublicensing is not allowed; section 10
makes it unnecessary.

  3. Protecting Users' Legal Rights From Anti-Circumvention Law.

  No covered work shall be deemed part of an effective technological
measure under any applicable law fulfilling obligations under article
11 of the WIPO copyright treaty adopted on 20 December 1996, or
similar laws prohibiting or restricting circumvention of such
measures.

  When you convey a covered work, you waive any legal power to forbid
circumvention of technological measures to the extent such circumvention
is effected by exercising rights under this License with respect to
the covered work, and you disclaim any intention to limit operation or
modification of the work as a means of enforcing, against the work's
users, your or third parties' legal rights to forbid circumvention of
technological measures.

  4. Conveying Verbatim Copies.

  You may convey verbatim copies of the Program's source code as you
receive it, in any medium, provided that you conspicuously and
appropriately publish on each copy an appropriate copyright notice;
keep intact all notices stating that this License and any
non-permissive terms added in accord with section 7 apply to the code;
keep intact all notices of the absence of any warranty; and give all
recipients a copy of this License along with the Program.

  You may charge any price or no price for each copy that you convey,
and you may offer support or warranty protection for a fee.

  5. Conveying Modified Source Versions.

  You may convey a work based on the Program, or the modifications to
produce it from the Program, in the form of source code under the
terms of section 4, provided that you also meet all of these conditions:

    a) The work must carry prominent notices stating that you modified
    it, and giving a relevant date.

    b) The work must carry prominent notices stating that it is
    released under this License and any conditions added under section
    7.  This requirement modifies the requirement in section 4 to
    "keep intact all notices".

    c) You must license the entire work, as a whole, under this
    License to anyone who comes into possession of a copy.  This
    License will therefore apply, along with any applicable section 7
    additional terms, to the whole of the work, and all its parts,
    regardless of how they are packaged.  This License gives no
    permission to license the work in any other way, but it does not
    invalidate such permission if you have separately received it.

    d) If the work has interactive user interfaces, each must display
    Appropriate Legal Notices; however, if the Program has interactive
    interfaces that do not display Appropriate Legal Notices, your
    work need not make them do so.

  A compilation of a covered work with other separate and independent
works, which are not by their nature extensions of the covered work,
and which are not combined with it such as to form a larger program,
in or on a volume of a storage or distribution medium, is called an
"aggregate" if the compilation and its resulting copyright are not
used to limit the access or legal rights of the compilation's users
beyond what the individual works permit.  Inclusion of a covered work
in an aggregate does not cause this License to apply to the other
parts of the aggregate.

  6. Conveying Non-Source Forms.

  You may convey a covered work in object code form under the terms
of sections 4 and 5, provided that you also convey the
machine-readable Corresponding Source under the terms of this License,
in one of these ways:

    a) Convey the object code in, or embodied in, a physical product
    (including a physical distribution medium), accompanied by the
    Corresponding Source fixed on a durable physical medium
    customarily used for software interchange.

    b) Convey the object code in, or embodied in, a physical product
    (including a physical distribution medium), accompanied by a
    written offer, valid for at least three years and valid for as
    long as you offer spare parts or customer support for that product
    model, to give anyone who possesses the object code either (1) a
    copy of the Corresponding Source for all the software in the
    product that is covered by this License, on a durable physical
    medium customarily used for software interchange, for a price no
    more than your reasonable cost of physically performing this
    conveying of source, or (2) access to copy the
    Corresponding Source from a network server at no charge.

    c) Convey individual copies of the object code with a copy of the
    written offer to provide the Corresponding Source.  This
    alternative is allowed only occasionally and noncommercially, and
    only if you received the object code with such an offer, in accord
    with subsection 6b.

    d) Convey the object code by offering access from a designated
    place (gratis or for a charge), and offer equivalent access to the
    Corresponding Source in the same way through the same place at no
    further charge.  You need not require recipients to copy the
    Corresponding Source along with the object code.  If the place to
    copy the object code is a network server, the Corresponding Source
    may be on a different server (operated by you or a third party)
    that supports equivalent copying facilities, provided you maintain
    clear directions next to the object code saying where to find the
    Corresponding Source.  Regardless of what server hosts the
    Corresponding Source, you remain obligated to ensure that it is
    available for as long as needed to satisfy these requirements.

    e) Convey the object code using peer-to-peer transmission, provided
    you inform other peers where the object code and Corresponding
    Source of the work are being offered to the general public at no
    charge under subsection 6d.

  A separable portion of the object code, whose source code is excluded
from the Corresponding Source as a System Library, need not be
included in conveying the object code work.

  A "User Product" is either (1) a "consumer product", which means any
tangible personal property which is normally used for personal, family,
or household purposes, or (2) anything designed or sold for incorporation
into a dwelling.  In determining whether a product is a consumer product,
doubtful cases shall be resolved in favor of coverage.  For a particular
product received by a particular user, "normally used" refers to a
typical or common use of that class of product, regardless of the status
of the particular user or of the way in which the particular user
actually uses, or expects or is expected to use, the product.  A product
is a consumer product regardless of whether the product has substantial
commercial, industrial or non-consumer uses, unless such uses represent
the only significant mode of use of the product.

  "Installation Information" for a User Product means any methods,
procedures, authorization keys, or other information required to install
and execute modified versions of a covered work in that User Product from
a modified version of its Corresponding Source.  The information must
suffice to ensure that the continued functioning of the modified object
code is in no case prevented or interfered with solely because
modification has been made.

  If you convey an object code work under this section in, or with, or
specifically for use in, a User Product, and the conveying occurs as
part of a transaction in which the right of possession and use of the
User Product is transferred to the recipient in perpetuity or for a
fixed term (regardless of how the transaction is characterized), the
Corresponding Source conveyed under this section must be accompanied
by the Installation Information.  But this requirement does not apply
if neither you nor any third party retains the ability to install
modified object code on the User Product (for example, the work has
been installed in ROM).

  The requirement to provide Installation Information does not include a
requirement to continue to provide support service, warranty, or updates
for a work that has been modified or installed by the recipient, or for
the User Product in which it has been modified or installed.  Access to a
network may be denied when the modification itself materially and
adversely affects the operation of the network or violates the rules and
protocols for communication across the network.

  Corresponding Source conveyed, and Installation Information provided,
in accord with this section must be in a format that is publicly
documented (and with an implementation available to the public in
source code form), and must require no special password or key for
unpacking, reading or copying.

  7. Additional Terms.

  "Additional permissions" are terms that supplement the terms of this
License by making exceptions from one or more of its conditions.
Additional permissions that are applicable to the entire Program shall
be treated as though they were included in this License, to the extent
that they are valid under applicable law.  If additional permissions
apply only to part of the Program, that part may be used separately
under those permissions, but the entire Program remains governed by
this License without regard to the additional permissions.

  When you convey a copy of a covered work, you may at your option
remove any additional permissions from that copy, or from any part of
it.  (Additional permissions may be written to require their own
removal in certain cases when you modify the work.)  You may place
additional permissions on material, added by you to a covered work,
for which you have or can give appropriate copyright permission.

  Notwithstanding any other provision of this License, for material you
add to a covered work, you may (if authorized by the copyright holders of
that material) supplement the terms of this License with terms:

    a) Disclaiming warranty or limiting liability differently from the
    terms of sections 15 and 16 of this License; or

    b) Requiring preservation of specified reasonable legal notices or
    author attributions in that material or in the Appropriate Legal
    Notices displayed by works containing it; or

    c) Prohibiting misrepresentation of the origin of that material, or
    requiring that modified versions of such material be marked in
    reasonable ways as different from the original version; or

    d) Limiting the use for publicity purposes of names of licensors or
    authors of the material; or

    e) Declining to grant rights under trademark law for use of some
    trade names, trademarks, or service marks; or

    f) Requiring indemnification of licensors and authors of that
    material by anyone who conveys the material (or modified versions of
    it) with contractual assumptions of liability to the recipient, for
    any liability that these contractual assumptions directly impose on
    those licensors and authors.

  All other non-permissive additional terms are considered "further
restrictions" within the meaning of section 10.  If the Program as you
received it, or any part of it, contains a notice stating that it is
governed by this License along with a term that is a further
restriction, you may remove that term.  If a license document contains
a further restriction but permits relicensing or conveying under this
License, you may add to a covered work material governed by the terms
of that license document, provided that the further restriction does
not survive such relicensing or conveying.

  If you add terms to a covered work in accord with this section, you
must place, in the relevant source files, a statement of the
additional terms that apply to those files, or a notice indicating
where to find the applicable terms.

  Additional terms, permissive or non-permissive, may be stated in the
form of a separately written license, or stated as exceptions;
the above requirements apply either way.

  8. Termination.

  You may not propagate or modify a covered work except as expressly
provided under this License.  Any attempt otherwise to propagate or
modify it is void, and will automatically terminate your rights under
this License (including any patent licenses granted under the third
paragraph of section 11).

  However, if you cease all violation of this License, then your
license from a particular copyright holder is reinstated (a)
provisionally, unless and until the copyright holder explicitly and
finally terminates your license, and (b) permanently, if the copyright
holder fails to notify you of the violation by some reasonable means
prior to 60 days after the cessation.

  Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from that
copyright holder, and you cure the violation prior to 30 days after
your receipt of the notice.

  Termination of your rights under this section does not terminate the
licenses of parties who have received copies or rights from you under
this License.  If your rights have been terminated and not permanently
reinstated, you do not qualify to receive new licenses for the same
material under section 10.

  9. Acceptance Not Required for Having Copies.

  You are not required to accept this License in order to receive or
run a copy of the Program.  Ancillary propagation of a covered work
occurring solely as a consequence of using peer-to-peer transmission
to receive a copy likewise does not require acceptance.  However,
nothing other than this License grants you permission to propagate or
modify any covered work.  These actions infringe copyright if you do
not accept this License.  Therefore, by modifying or propagating a
covered work, you indicate your acceptance of this License to do so.

  10. Automatic Licensing of Downstream Recipients.

  Each time you convey a covered work, the recipient automatically
receives a license from the original licensors, to run, modify and
propagate that work, subject to this License.  You are not responsible
for enforcing compliance by third parties with this License.

  An "entity transaction" is a transaction transferring control of an
organization, or substantially all assets of one, or subdividing an
organization, or merging organizations.  If propagation of a covered
work results from an entity transaction, each party to that
transaction who receives a copy of the work also receives whatever
licenses to the work the party's predecessor in interest had or could
give under the previous paragraph, plus a right to possession of the
Corresponding Source of the work from the predecessor in interest, if
the predecessor has it or can get it with reasonable efforts.

  You may not impose any further restrictions on the exercise of the
rights granted or affirmed under this License.  For example, you may
not impose a license fee, royalty, or other charge for exercise of
rights granted under this License, and you may not initiate litigation
(including a cross-claim or counterclaim in a lawsuit) alleging that
any patent claim is infringed by making, using, selling, offering for
sale, or importing the Program or any portion of it.

  11. Patents.

  A "contributor" is a copyright holder who authorizes use under this
License of the Program or a work on which the Program is based.  The
work thus licensed is called the contributor's "contributor version".

  A contributor's "essential patent claims" are all patent claims
owned or controlled by the contributor, whether already acquired or
hereafter acquired, that would be infringed by some manner, permitted
by this License, of making, using, or selling its contributor version,
but do not include claims that would be infringed only as a
consequence of further modification of the contributor version.  For
purposes of this definition, "control" includes the right to grant
patent sublicenses in a manner consistent with the requirements of
this License.

  Each contributor grants you a non-exclusive, worldwide, royalty-free
patent license under the contributor's essential patent claims, to
make, use, sell, offer for sale, import and otherwise run, modify and
propagate the contents of its contributor version.

  In the following three paragraphs, a "patent license" is any express
agreement or commitment, however denominated, not to enforce a patent
(such as an express permission to practice a patent or covenant not to
sue for patent infringement).  To "grant" such a patent license to a
party means to make such an agreement or commitment not to enforce a
patent against the party.

  If you convey a covered work, knowingly relying on a patent license,
and the Corresponding Source of the work is not available for anyone
to copy, free of charge and under the terms of this License, through a
publicly available network server or other readily accessible means,
then you must either (1) cause the Corresponding Source to be so
available, or (2) arrange to deprive yourself of the benefit of the
patent license for this particular work, or (3) arrange, in a manner
consistent with the requirements of this License, to extend the patent
license to downstream recipients.  "Knowingly relying" means you have
actual knowledge that, but for the patent license, your conveying the
covered work in a country, or your recipient's use of the covered work
in a country, would infringe one or more identifiable patents in that
country that you have reason to believe are valid.

  If, pursuant to or in connection with a single transaction or
arrangement, you convey, or propagate by procuring conveyance of, a
covered work, and grant a patent license to some of the parties
receiving the covered work authorizing them to use, propagate, modify
or convey a specific copy of the covered work, then the patent license
you grant is automatically extended to all recipients of the covered
work and works based on it.

  A patent license is "discriminatory" if it does not include within
the scope of its coverage, prohibits the exercise of, or is
conditioned on the non-exercise of one or more of the rights that are
specifically granted under this License.  You may not convey a covered
work if you are a party to an arrangement with a third party that is
in the business of distributing software, under which you make payment
to the third party based on the extent of your activity of conveying
the work, and under which the third party grants, to any of the
parties who would receive the covered work from you, a discriminatory
patent license (a) in connection with copies of the covered work
conveyed by you (or copies made from those copies), or (b) primarily
for and in connection with specific products or compilations that
contain the covered work, unless you entered into that arrangement,
or that patent license was granted, prior to 28 March 2007.

  Nothing in this License shall be construed as excluding or limiting
any implied license or other defenses to infringement that may
otherwise be available to you under applicable patent law.

  12. No Surrender of Others' Freedom.

  If conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License.  If you cannot convey a
covered work so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you may
not convey it at all.  For example, if you agree to terms that obligate you
to collect a royalty for further conveying from those to whom you convey
the Program, the only way you could satisfy both those terms and this
License would be to refrain entirely from conveying the Program.

  13. Use with the GNU Affero General Public License.

  Notwithstanding any other provision of this License, you have
permission to link or combine any covered work with a work licensed
under version 3 of the GNU Affero General Public License into a single
combined work, and to convey the resulting work.  The terms of this
License will continue to apply to the part which is the covered work,
but the special requirements of the GNU Affero General Public License,
section 13, concerning interaction through a network will apply to the
combination as such.

  14. Revised Versions of this License.

  The Free Software Foundation may publish revised and/or new versions of
the GNU General Public License from time to time.  Such new versions will
be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.

  Each version is given a distinguishing version number.  If the
Program specifies that a certain numbered version of the GNU General
Public License "or any later version" applies to it, you have the
option of following the terms and conditions either of that numbered
version or of any later version published by the Free Software
Foundation.  If the Program does not specify a version number of the
GNU General Public License, you may choose any version ever published
by the Free Software Foundation.

  If the Program specifies that a proxy can decide which future
versions of the GNU General Public License can be used, that proxy's
public statement of acceptance of a version permanently authorizes you
to choose that version for the Program.

  Later license versions may give you additional or different
permissions.  However, no additional obligations are imposed on any
author or copyright holder as a result of your choosing to follow a
later version.

  15. Disclaimer of Warranty.

  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

  16. Limitation of Liability.

  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES.

  17. Interpretation of Sections 15 and 16.

  If the disclaimer of warranty and limitation of liability provided
above cannot be given local legal effect according to their terms,
reviewing courts shall apply local law that most closely approximates
an absolute waiver of all civil liability in connection with the
Program, unless a warranty or assumption of liability accompanies a
copy of the Program in return for a fee.

                     END OF TERMS AND CONDITIONS

            How to Apply These Terms to Your New Programs

  If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these terms.

  To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.

    <one line to give the program's name and a brief idea of what it does.>
    Copyright (C) <year>  <name of author>

    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/>.

Also add information on how to contact you by electronic and paper mail.

  If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:

    <program>  Copyright (C) <year>  <name of author>
    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
    This is free software, and you are welcome to redistribute it
    under certain conditions; type `show c' for details.

The hypothetical commands `show w' and `show c' should show the appropriate
parts of the General Public License.  Of course, your program's commands
might be different; for a GUI interface, you would use an "about box".

  You should also get your employer (if you work as a programmer) or school,
if any, to sign a "copyright disclaimer" for the program, if necessary.
For more information on this, and how to apply and follow the GNU GPL, see
<http://www.gnu.org/licenses/>.

  The GNU General Public License does not permit incorporating your program
into proprietary programs.  If your program is a subroutine library, you
may consider it more useful to permit linking proprietary applications with
the library.  If this is what you want to do, use the GNU Lesser General
Public License instead of this License.  But first, please read
<http://www.gnu.org/philosophy/why-not-lgpl.html>.

Creative Commons Attribution-ShareAlike 4.0 International

Attribution-ShareAlike 4.0 International

=======================================================================

Creative Commons Corporation ("Creative Commons") is not a law firm and
does not provide legal services or legal advice. Distribution of
Creative Commons public licenses does not create a lawyer-client or
other relationship. Creative Commons makes its licenses and related
information available on an "as-is" basis. Creative Commons gives no
warranties regarding its licenses, any material licensed under their
terms and conditions, or any related information. Creative Commons
disclaims all liability for damages resulting from their use to the
fullest extent possible.

Using Creative Commons Public Licenses

Creative Commons public licenses provide a standard set of terms and
conditions that creators and other rights holders may use to share
original works of authorship and other material subject to copyright
and certain other rights specified in the public license below. The
following considerations are for informational purposes only, are not
exhaustive, and do not form part of our licenses.

     Considerations for licensors: Our public licenses are
     intended for use by those authorized to give the public
     permission to use material in ways otherwise restricted by
     copyright and certain other rights. Our licenses are
     irrevocable. Licensors should read and understand the terms
     and conditions of the license they choose before applying it.
     Licensors should also secure all rights necessary before
     applying our licenses so that the public can reuse the
     material as expected. Licensors should clearly mark any
     material not subject to the license. This includes other CC-
     licensed material, or material used under an exception or
     limitation to copyright. More considerations for licensors:
	wiki.creativecommons.org/Considerations_for_licensors

     Considerations for the public: By using one of our public
     licenses, a licensor grants the public permission to use the
     licensed material under specified terms and conditions. If
     the licensor's permission is not necessary for any reason--for
     example, because of any applicable exception or limitation to
     copyright--then that use is not regulated by the license. Our
     licenses grant only permissions under copyright and certain
     other rights that a licensor has authority to grant. Use of
     the licensed material may still be restricted for other
     reasons, including because others have copyright or other
     rights in the material. A licensor may make special requests,
     such as asking that all changes be marked or described.
     Although not required by our licenses, you are encouraged to
     respect those requests where reasonable. More_considerations
     for the public: 
	wiki.creativecommons.org/Considerations_for_licensees

=======================================================================

Creative Commons Attribution-ShareAlike 4.0 International Public
License

By exercising the Licensed Rights (defined below), You accept and agree
to be bound by the terms and conditions of this Creative Commons
Attribution-ShareAlike 4.0 International Public License ("Public
License"). To the extent this Public License may be interpreted as a
contract, You are granted the Licensed Rights in consideration of Your
acceptance of these terms and conditions, and the Licensor grants You
such rights in consideration of benefits the Licensor receives from
making the Licensed Material available under these terms and
conditions.


Section 1 -- Definitions.

  a. Adapted Material means material subject to Copyright and Similar
     Rights that is derived from or based upon the Licensed Material
     and in which the Licensed Material is translated, altered,
     arranged, transformed, or otherwise modified in a manner requiring
     permission under the Copyright and Similar Rights held by the
     Licensor. For purposes of this Public License, where the Licensed
     Material is a musical work, performance, or sound recording,
     Adapted Material is always produced where the Licensed Material is
     synched in timed relation with a moving image.

  b. Adapter's License means the license You apply to Your Copyright
     and Similar Rights in Your contributions to Adapted Material in
     accordance with the terms and conditions of this Public License.

  c. BY-SA Compatible License means a license listed at
     creativecommons.org/compatiblelicenses, approved by Creative
     Commons as essentially the equivalent of this Public License.

  d. Copyright and Similar Rights means copyright and/or similar rights
     closely related to copyright including, without limitation,
     performance, broadcast, sound recording, and Sui Generis Database
     Rights, without regard to how the rights are labeled or
     categorized. For purposes of this Public License, the rights
     specified in Section 2(b)(1)-(2) are not Copyright and Similar
     Rights.

  e. Effective Technological Measures means those measures that, in the
     absence of proper authority, may not be circumvented under laws
     fulfilling obligations under Article 11 of the WIPO Copyright
     Treaty adopted on December 20, 1996, and/or similar international
     agreements.

  f. Exceptions and Limitations means fair use, fair dealing, and/or
     any other exception or limitation to Copyright and Similar Rights
     that applies to Your use of the Licensed Material.

  g. License Elements means the license attributes listed in the name
     of a Creative Commons Public License. The License Elements of this
     Public License are Attribution and ShareAlike.

  h. Licensed Material means the artistic or literary work, database,
     or other material to which the Licensor applied this Public
     License.

  i. Licensed Rights means the rights granted to You subject to the
     terms and conditions of this Public License, which are limited to
     all Copyright and Similar Rights that apply to Your use of the
     Licensed Material and that the Licensor has authority to license.

  j. Licensor means the individual(s) or entity(ies) granting rights
     under this Public License.

  k. Share means to provide material to the public by any means or
     process that requires permission under the Licensed Rights, such
     as reproduction, public display, public performance, distribution,
     dissemination, communication, or importation, and to make material
     available to the public including in ways that members of the
     public may access the material from a place and at a time
     individually chosen by them.

  l. Sui Generis Database Rights means rights other than copyright
     resulting from Directive 96/9/EC of the European Parliament and of
     the Council of 11 March 1996 on the legal protection of databases,
     as amended and/or succeeded, as well as other essentially
     equivalent rights anywhere in the world.

  m. You means the individual or entity exercising the Licensed Rights
     under this Public License. Your has a corresponding meaning.


Section 2 -- Scope.

  a. License grant.

       1. Subject to the terms and conditions of this Public License,
          the Licensor hereby grants You a worldwide, royalty-free,
          non-sublicensable, non-exclusive, irrevocable license to
          exercise the Licensed Rights in the Licensed Material to:

            a. reproduce and Share the Licensed Material, in whole or
               in part; and

            b. produce, reproduce, and Share Adapted Material.

       2. Exceptions and Limitations. For the avoidance of doubt, where
          Exceptions and Limitations apply to Your use, this Public
          License does not apply, and You do not need to comply with
          its terms and conditions.

       3. Term. The term of this Public License is specified in Section
          6(a).

       4. Media and formats; technical modifications allowed. The
          Licensor authorizes You to exercise the Licensed Rights in
          all media and formats whether now known or hereafter created,
          and to make technical modifications necessary to do so. The
          Licensor waives and/or agrees not to assert any right or
          authority to forbid You from making technical modifications
          necessary to exercise the Licensed Rights, including
          technical modifications necessary to circumvent Effective
          Technological Measures. For purposes of this Public License,
          simply making modifications authorized by this Section 2(a)
          (4) never produces Adapted Material.

       5. Downstream recipients.

            a. Offer from the Licensor -- Licensed Material. Every
               recipient of the Licensed Material automatically
               receives an offer from the Licensor to exercise the
               Licensed Rights under the terms and conditions of this
               Public License.

            b. Additional offer from the Licensor -- Adapted Material.
               Every recipient of Adapted Material from You
               automatically receives an offer from the Licensor to
               exercise the Licensed Rights in the Adapted Material
               under the conditions of the Adapter's License You apply.

            c. No downstream restrictions. You may not offer or impose
               any additional or different terms or conditions on, or
               apply any Effective Technological Measures to, the
               Licensed Material if doing so restricts exercise of the
               Licensed Rights by any recipient of the Licensed
               Material.

       6. No endorsement. Nothing in this Public License constitutes or
          may be construed as permission to assert or imply that You
          are, or that Your use of the Licensed Material is, connected
          with, or sponsored, endorsed, or granted official status by,
          the Licensor or others designated to receive attribution as
          provided in Section 3(a)(1)(A)(i).

  b. Other rights.

       1. Moral rights, such as the right of integrity, are not
          licensed under this Public License, nor are publicity,
          privacy, and/or other similar personality rights; however, to
          the extent possible, the Licensor waives and/or agrees not to
          assert any such rights held by the Licensor to the limited
          extent necessary to allow You to exercise the Licensed
          Rights, but not otherwise.

       2. Patent and trademark rights are not licensed under this
          Public License.

       3. To the extent possible, the Licensor waives any right to
          collect royalties from You for the exercise of the Licensed
          Rights, whether directly or through a collecting society
          under any voluntary or waivable statutory or compulsory
          licensing scheme. In all other cases the Licensor expressly
          reserves any right to collect such royalties.


Section 3 -- License Conditions.

Your exercise of the Licensed Rights is expressly made subject to the
following conditions.

  a. Attribution.

       1. If You Share the Licensed Material (including in modified
          form), You must:

            a. retain the following if it is supplied by the Licensor
               with the Licensed Material:

                 i. identification of the creator(s) of the Licensed
                    Material and any others designated to receive
                    attribution, in any reasonable manner requested by
                    the Licensor (including by pseudonym if
                    designated);

                ii. a copyright notice;

               iii. a notice that refers to this Public License;

                iv. a notice that refers to the disclaimer of
                    warranties;

                 v. a URI or hyperlink to the Licensed Material to the
                    extent reasonably practicable;

            b. indicate if You modified the Licensed Material and
               retain an indication of any previous modifications; and

            c. indicate the Licensed Material is licensed under this
               Public License, and include the text of, or the URI or
               hyperlink to, this Public License.

       2. You may satisfy the conditions in Section 3(a)(1) in any
          reasonable manner based on the medium, means, and context in
          which You Share the Licensed Material. For example, it may be
          reasonable to satisfy the conditions by providing a URI or
          hyperlink to a resource that includes the required
          information.

       3. If requested by the Licensor, You must remove any of the
          information required by Section 3(a)(1)(A) to the extent
          reasonably practicable.

  b. ShareAlike.

     In addition to the conditions in Section 3(a), if You Share
     Adapted Material You produce, the following conditions also apply.

       1. The Adapter's License You apply must be a Creative Commons
          license with the same License Elements, this version or
          later, or a BY-SA Compatible License.

       2. You must include the text of, or the URI or hyperlink to, the
          Adapter's License You apply. You may satisfy this condition
          in any reasonable manner based on the medium, means, and
          context in which You Share Adapted Material.

       3. You may not offer or impose any additional or different terms
          or conditions on, or apply any Effective Technological
          Measures to, Adapted Material that restrict exercise of the
          rights granted under the Adapter's License You apply.


Section 4 -- Sui Generis Database Rights.

Where the Licensed Rights include Sui Generis Database Rights that
apply to Your use of the Licensed Material:

  a. for the avoidance of doubt, Section 2(a)(1) grants You the right
     to extract, reuse, reproduce, and Share all or a substantial
     portion of the contents of the database;

  b. if You include all or a substantial portion of the database
     contents in a database in which You have Sui Generis Database
     Rights, then the database in which You have Sui Generis Database
     Rights (but not its individual contents) is Adapted Material,

     including for purposes of Section 3(b); and
  c. You must comply with the conditions in Section 3(a) if You Share
     all or a substantial portion of the contents of the database.

For the avoidance of doubt, this Section 4 supplements and does not
replace Your obligations under this Public License where the Licensed
Rights include other Copyright and Similar Rights.


Section 5 -- Disclaimer of Warranties and Limitation of Liability.

  a. UNLESS OTHERWISE SEPARATELY UNDERTAKEN BY THE LICENSOR, TO THE
     EXTENT POSSIBLE, THE LICENSOR OFFERS THE LICENSED MATERIAL AS-IS
     AND AS-AVAILABLE, AND MAKES NO REPRESENTATIONS OR WARRANTIES OF
     ANY KIND CONCERNING THE LICENSED MATERIAL, WHETHER EXPRESS,
     IMPLIED, STATUTORY, OR OTHER. THIS INCLUDES, WITHOUT LIMITATION,
     WARRANTIES OF TITLE, MERCHANTABILITY, FITNESS FOR A PARTICULAR
     PURPOSE, NON-INFRINGEMENT, ABSENCE OF LATENT OR OTHER DEFECTS,
     ACCURACY, OR THE PRESENCE OR ABSENCE OF ERRORS, WHETHER OR NOT
     KNOWN OR DISCOVERABLE. WHERE DISCLAIMERS OF WARRANTIES ARE NOT
     ALLOWED IN FULL OR IN PART, THIS DISCLAIMER MAY NOT APPLY TO YOU.

  b. TO THE EXTENT POSSIBLE, IN NO EVENT WILL THE LICENSOR BE LIABLE
     TO YOU ON ANY LEGAL THEORY (INCLUDING, WITHOUT LIMITATION,
     NEGLIGENCE) OR OTHERWISE FOR ANY DIRECT, SPECIAL, INDIRECT,
     INCIDENTAL, CONSEQUENTIAL, PUNITIVE, EXEMPLARY, OR OTHER LOSSES,
     COSTS, EXPENSES, OR DAMAGES ARISING OUT OF THIS PUBLIC LICENSE OR
     USE OF THE LICENSED MATERIAL, EVEN IF THE LICENSOR HAS BEEN
     ADVISED OF THE POSSIBILITY OF SUCH LOSSES, COSTS, EXPENSES, OR
     DAMAGES. WHERE A LIMITATION OF LIABILITY IS NOT ALLOWED IN FULL OR
     IN PART, THIS LIMITATION MAY NOT APPLY TO YOU.

  c. The disclaimer of warranties and limitation of liability provided
     above shall be interpreted in a manner that, to the extent
     possible, most closely approximates an absolute disclaimer and
     waiver of all liability.


Section 6 -- Term and Termination.

  a. This Public License applies for the term of the Copyright and
     Similar Rights licensed here. However, if You fail to comply with
     this Public License, then Your rights under this Public License
     terminate automatically.

  b. Where Your right to use the Licensed Material has terminated under
     Section 6(a), it reinstates:

       1. automatically as of the date the violation is cured, provided
          it is cured within 30 days of Your discovery of the
          violation; or

       2. upon express reinstatement by the Licensor.

     For the avoidance of doubt, this Section 6(b) does not affect any
     right the Licensor may have to seek remedies for Your violations
     of this Public License.

  c. For the avoidance of doubt, the Licensor may also offer the
     Licensed Material under separate terms or conditions or stop
     distributing the Licensed Material at any time; however, doing so
     will not terminate this Public License.

  d. Sections 1, 5, 6, 7, and 8 survive termination of this Public
     License.


Section 7 -- Other Terms and Conditions.

  a. The Licensor shall not be bound by any additional or different
     terms or conditions communicated by You unless expressly agreed.

  b. Any arrangements, understandings, or agreements regarding the
     Licensed Material not stated herein are separate from and
     independent of the terms and conditions of this Public License.


Section 8 -- Interpretation.

  a. For the avoidance of doubt, this Public License does not, and
     shall not be interpreted to, reduce, limit, restrict, or impose
     conditions on any use of the Licensed Material that could lawfully
     be made without permission under this Public License.

  b. To the extent possible, if any provision of this Public License is
     deemed unenforceable, it shall be automatically reformed to the
     minimum extent necessary to make it enforceable. If the provision
     cannot be reformed, it shall be severed from this Public License
     without affecting the enforceability of the remaining terms and
     conditions.

  c. No term or condition of this Public License will be waived and no
     failure to comply consented to unless expressly agreed to by the
     Licensor.

  d. Nothing in this Public License constitutes or may be interpreted
     as a limitation upon, or waiver of, any privileges and immunities
     that apply to the Licensor or You, including from the legal
     processes of any jurisdiction or authority.


=======================================================================

Creative Commons is not a party to its public
licenses. Notwithstanding, Creative Commons may elect to apply one of
its public licenses to material it publishes and in those instances
will be considered the “Licensor.” The text of the Creative Commons
public licenses is dedicated to the public domain under the CC0 Public
Domain Dedication. Except for the limited purpose of indicating that
material is shared under a Creative Commons public license or as
otherwise permitted by the Creative Commons policies published at
creativecommons.org/policies, Creative Commons does not authorize the
use of the trademark "Creative Commons" or any other trademark or logo
of Creative Commons without its prior written consent including,
without limitation, in connection with any unauthorized modifications
to any of its public licenses or any other arrangements,
understandings, or agreements concerning use of licensed material. For
the avoidance of doubt, this paragraph does not form part of the
public licenses.

Creative Commons may be contacted at creativecommons.org.

TODO

Todo

Write pull request review guidelines

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flycheck/checkouts/29/doc/contributor/maintaining.rst, line 97.)

Todo

Port the old manual

Meanwhile see flycheck.html for a simple HTML version of the old manual.

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flycheck/checkouts/29/doc/index.rst, line 71.)

Todo

Port the extending section from the old manual

Meanwhile see flycheck.html for a simple HTML version of the old manual.

(The original entry is located in /home/docs/checkouts/readthedocs.org/user_builds/flycheck/checkouts/29/doc/index.rst, line 94.)