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.

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

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 Eask, 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.
make compile compiles Flycheck and its libraries to byte code.
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.

Testing a checker without its tool¶

Most of the tools Flycheck drives are not installed on any given machine, and a spec that needs a missing tool skips itself. That keeps the suite runnable everywhere, but it also means a checker can stop working without a single test going red.

So the part that usually breaks — reading the tool’s output — is tested against output recorded earlier, which needs nothing installed:

$ emacs -Q --batch -l test/record-fixture.el \
    -f flycheck-record-fixture-batch sh-shellcheck language/sh/shellcheck.sh

That runs the checker’s own command, the one Flycheck would run, and writes what the tool printed to test/fixtures/checker/resource.txt. A spec then asserts what Flycheck reads back out of it:

(flycheck-buttercup-def-parse-test json-jq "language/json.json"
  '(1 44 error "Expected value before ','"))

Record the output on a machine that has the tool, commit it, and the spec runs for everyone. When a tool changes its format, re-record and the diff shows exactly what moved.

Testing your checker in the developer’s guide covers this from the other end, for somebody adding a checker rather than maintaining one, and lists the mistakes that keep being made.

The catch is that a recording says what the tool printed on the day it was made, and the spec reading it keeps passing whatever the tool does afterwards. make verify-fixtures closes that: it runs the tools that are installed and checks that Flycheck still reads errors out of them.

It deliberately does not compare the text. A recording is made on somebody’s machine, and the same checker meets a different build of the tool elsewhere, so comparing would report a difference every week until nobody read the report. A checker that read errors when its output was recorded and reads none now has stopped understanding its tool, which is what every one of these has looked like: jq grew a prefix, rebar3 replaced its format, the byte compiler moved a warning onto one line.

That target only reaches the tools the machine running it happens to have, so there is a second one that runs the check inside the image described below:

$ make verify-fixtures-image

This reaches nearly every recording rather than the handful a given machine can answer for, which is why it is the one the weekly job runs. A pull request that touches a recording gets the quicker, thinner check instead, so the answer arrives while somebody is still looking at it.

Recording in bulk¶

Nobody has all of Flycheck’s checkers installed, so there is an image with as many of them as is practical:

$ make record-fixtures

That builds test/docker/Dockerfile, mounts your checkout into it, and records every checker whose tool it has and whose spec names a file to check. make checker-shell drops you into the same container if you would rather poke at a tool by hand. The image is the current Ubuntu LTS, and the weekly job runs inside it too, so what comes out of a recording session is what that job later sees.

Recording in bulk will not write a recording that its own checker reads nothing out of, because that is what a tool failing to start looks like: credo without a mix.exs, the Go checkers without a module. Those are reported instead, and can be recorded by hand if the output really is what the tool has to say.

Read what it wrote before committing it. A recording nobody looked at is the same trap as a spec that never ran.

Because your checkout is mounted rather than copied, anything a build on your own machine left in it goes into the container too, and a tool that meets a build artefact from a different version of itself can fail in ways that read exactly like a checker that stopped understanding its tool. A stale _build under the rebar3 resource is the one that has actually happened: rebar3 could not read the .beam files a newer Erlang had written and died before it compiled anything. git clean -xfd test/resources before a run that reports something surprising.

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 check specs unit 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, the continuous integration will test your changes, too.

All pull requests go through a two-stage review process:

Maintainer review the general idea and direction of the pull request and leave a LGTM comment if they believe that the change is a good addition to Flycheck. We currently require at least one approval from a maintainer.
All contributors—language teams in particular—check the technical implementation of a pull request through pull request reviews, and either approve it or request changes. We currently require at least one approval and no requested changes.

Important

We have a comprehensive Style Guide that explains what features we will accept, how our code should look like, what tests we require, how commit messages should look like, and so on.

Take a look at it to see what we look for in a code review.

Additionally all pull requests go through automated tests on GitHub Actions which check code style, run tests, etc.

Feel free to mention individual contributors or entire teams (e.g. @flycheck/maintainers or @flycheck/javascript) to ask for help or feedback or request a review. Please mention the maintainers (@flycheck/maintainers) if you think that your pull request has been waiting for review too long. You can expect a first response to any pull request in a couple of days.

Once the pull request passed review and automated tests we will merge it. We may also ask you whether you’d like to join Flycheck and help us, thus giving you commit access to our repository and let you merge your own pull request.

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 3.9 or newer to install Sphinx for Flycheck’s documentation. On macOS 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 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 a virtual environment 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 have 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 on StackExchange or on our issue tracker.

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.