Everyone is welcome to contribute code to Matrix (https://github.com/matrix-org), provided that they are willing to license their contributions under the same license as the project itself. We follow a simple 'inbound=outbound' model for contributions: the act of submitting an 'inbound' contribution means that the contributor agrees to license the code under the same terms as the project's overall 'outbound' license - in our case, this is almost always Apache Software License v2 (see LICENSE).
The preferred and easiest way to contribute changes to Matrix is to fork the relevant project on github, and then create a pull request to ask us to pull your changes into our repo (https://help.github.com/articles/using-pull-requests/)
The single biggest thing you need to know is: please base your changes on the develop branch - /not/ master.
We use the master branch to track the most recent release, so that folks who blindly clone the repo and automatically check out master get something that works. Develop is the unstable branch where all the development actually happens: the workflow is that contributors should fork the develop branch to make a 'feature' branch for a particular contribution, and then make a pull request to merge this back into the matrix.org 'official' develop branch. We use github's pull request workflow to review the contribution, and either ask you to make any refinements needed or merge it and make them ourselves. The changes will then land on master when we next do a release.
We use Jenkins for continuous integration (http://matrix.org/jenkins), and typically all pull requests get automatically tested Jenkins: if your change breaks the build, Jenkins will yell about it in #matrix-dev:matrix.org so please lurk there and keep an eye open.
All Matrix projects have a well-defined code-style - and sometimes we've even got as far as documenting it... For instance, synapse's code style doc lives at https://github.com/matrix-org/synapse/tree/master/docs/code_style.rst.
Please ensure your changes match the cosmetic style of the existing project, and never mix cosmetic and functional changes in the same commit, as it makes it horribly hard to review otherwise.
Everyone who contributes anything to Matrix is welcome to be listed in the AUTHORS.rst file for the project in question. Please feel free to include a change to AUTHORS.rst in your pull request to list yourself and a short description of the area(s) you've worked on. Also, we sometimes have swag to give away to contributors - if you feel that Matrix-branded apparel is missing from your life, please mail us your shipping address to matrix at matrix.org and we'll try to fix it :)
In order to have a concrete record that your contribution is intentional and you agree to license it under the same terms as the project's license, we've adopted the same lightweight approach that the Linux Kernel (https://www.kernel.org/doc/Documentation/SubmittingPatches), Docker (https://github.com/docker/docker/blob/master/CONTRIBUTING.md), and many other projects use: the DCO (Developer Certificate of Origin: http://developercertificate.org/). This is a simple declaration that you wrote the contribution or otherwise have the right to contribute it to Matrix:
Developer Certificate of Origin
Version 1.1
Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
660 York Street, Suite 102,
San Francisco, CA 94110 USA
Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
Developer's Certificate of Origin 1.1
By making a contribution to this project, I certify that:
(a) The contribution was created in whole or in part by me and I
have the right to submit it under the open source license
indicated in the file; or
(b) The contribution is based upon previous work that, to the best
of my knowledge, is covered under an appropriate open source
license and I have the right under that license to submit that
work with modifications, whether created in whole or in part
by me, under the same open source license (unless I am
permitted to submit under a different license), as indicated
in the file; or
(c) The contribution was provided directly to me by some other
person who certified (a), (b) or (c) and I have not modified
it.
(d) I understand and agree that this project and the contribution
are public and that a record of the contribution (including all
personal information I submit with it, including my sign-off) is
maintained indefinitely and may be redistributed consistent with
this project or the open source license(s) involved.If you agree to this for your contribution, then all that's needed is to include the line in your commit or pull request comment:
Signed-off-by: Your Name <your@email.example.org>...using your real name; unfortunately pseudonyms and anonymous contributions can't be accepted. Git makes this trivial - just use the -s flag when you do git commit, having first set user.name and user.email git configs (which you should have done anyway :)
That's it! Matrix is a very open and collaborative project as you might expect given our obsession with open communication. If we're going to successfully matrix together all the fragmented communication technologies out there we are reliant on contributions and collaboration from the community to do so. So please get involved - and we hope you have as much fun hacking on Matrix as we do!