How to become a MediaWiki hacker/oc

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This article is written to help developers learn the basic skills needed to contribute to development of MediaWiki core and MediaWiki extensions. Note that in most cases when working with MediaWiki, you do not want to hack MediaWiki core unless you really know what you're doing.

The main path to get started with Wikimedia development is to contribute to Wikimedia projects that offer mentoring. An alternative without mentoring is to fix an annoying little bug.

If you are an experienced developer who is familiar with using MediaWiki already, visit the Developer hubDeveloper hub instead.

For other ways to get involved in the Wikimedia community, see Cossí contribuirHow to contribute.

Overview

MediaWiki is the software that powers Wikipedia, its sister projects and thousands of wikis all over the world. It runs on most operating systems, is written in PHP, primarily uses the MySQL and MariaDB database servers and uses jQuery as the client JavaScript library. Development of MediaWiki is primarily supported by the Wikimedia Foundation, though volunteer community developers play a huge part as well.

This page should help you become a contributor to MediaWiki. It is not a tutorial; it just points you to various places where you can go learn whatever is necessary.

Set up your development environment

Most projects use Git and Gerrit. Follow the Gerrit tutorial to set up your developer account. Then you can move on to downloading our code, making changes, testing them, and submitting patches. There are two ways to set up your development environment: using a pre-configured virtual machine setup (vagrant), or manual.

Virtual Machine with Vagrant

  • Vagrant installation - These steps will install MediaWiki server with all the requirements inside a Linux virtual machine (can be used on Linux, Windows, or Mac hosts)

Manual installation

It's not necessary to download Wikipedia database dumps in order to develop MediaWiki features. In fact, in many cases it's easier to use a near-empty database with a few specially-crafted test pages. However, if for some reason you want to have a copy of Wikipedia, you can get a dump.

Suggested reading

Watch as a developer fixes a bug in a MediaWiki extension, including investigation, git commit, getting it reviewed and merged, and closing the Bugzilla ticket (now replaced by PhabricatorPhabricator).

Feedback, questions and support

  • You are expected to do some basic research yourself first: Look at the code, try to get some understanding what it is supposed to do, read related documentation, try to find the probable place(s) where you need to make changes in order to fix the bug.
  • If you have general questions about infrastructure (Git, Gerrit, Vagrant), the software architecture or workflows which are not tied to the specific task that you want to work on, use generic channels like IRCIRC, mailing lists, or wiki discussion pages but not the specific task. For example, if you have a problem with Gerrit, the Gerrit discussion page could be a good place to ask.
  • If you have a specific question about the bug itself, comment in the corresponding bug report (normally a task in PhabricatorPhabricator). "Can you give me more info how to fix this bug?" is not a good question to start with: The more specific your questions are, the more likely somebody can answer them quickly. If you have no idea at all how to fix the bug, maybe that bug is not (yet) for you - please consider finding an easier one first.
  • When asking, explain what you have tried and found out already, so others can help at the right level. Be specific - for example, copy and paste your commands and their output (if not too long) instead of paraphrasing in your own words. This avoids misunderstandings.
  • Avoid private email or support requests in our social media channels.
  • Be patient when seeking input and comments. On IRC, don't ask to ask, just ask: most questions can be answered by other community members too if you ask on an IRC channel. If nobody answers, please ask on the bug report or wiki page related to the problem; don't just give up.
  • Learn more at ComunicacionCommunication.
  • You can also ask any questions at the weekly Technical Advice IRC Meeting on the #wikimedia-tech channel on Freenode IRC.


Communicate that you work on a task

You do not need to ask if you can work on a task. You do not need to be set as the assignee in a task or announce your plans before you start working on a bug, but it would be welcome. At the latest when you are close to proposing a patch for the task, it is good to announce in a comment that you are working on it. Your announcement helps others to not work on the bug at the same time and to not duplicate work.

Also note that if a task already has a recent link to a patch in Gerrit and has the project "Patch-For-Review" associated in Phabricator, choose a different task to work on instead - avoid duplicating work. If an existing patch in Gerrit has not been merged and has not seen any changes for a long time, you could also pick up that existing patch and improve it, based on the feedback in Gerrit and in the task.

If you stop working on a task, remove yourself as the assignee of the task, so others know that they can work on the task and don't expect you to still work on it.

By communicating early you will get more attention, feedback and help from community members.


Appendix

MediaWiki contributors at work in Bangalore, India.

PHP

MediaWiki is written in PHP, so you'll need to get familiar with PHP to hack MediaWiki's core.

Learn PHP
  • PHP tutorial — Available in many different languages. If you have no knowledge of PHP but know how to program in other object-oriented programming languages, PHP will be easy for you to learn.
  • PHP Programming at Wikibooks.
  • PHP topic at Wikiversity.
PHP resources
Stuff to know
  • The script maintenance/eval.php in MediaWiki provides a basic PHP interpreter with MediaWiki objects and classes loaded.

Database

Many features require some amount of database manipulation, so you'll often need to be familiar with MySQL/MariaDB.

Learn MySQL/MariaDB
MySQL/MariaDB resources
Stuff to know
  • Test your code with MySQL/MariaDB.
    • MediaWiki currently uses MySQL and MariaDB as the primary database back-end. It also supports other DBMSes, such as PostgreSQL and SQLite. However, almost all developers use MySQL/MariaDB and don't test other DBs, which consequently break on a regular basis. You're therefore advised to use MySQL/MariaDB when testing patches, unless you're specifically trying to improve support for another DB. In the latter case, make sure you're careful not to break MySQL/MariaDB (or write queries that are horribly inefficient in it), since MySQL/MariaDB is what everybody else uses.

JavaScript and CSS

JavaScript and CSS have become omnipresent in front-end code. Alma Karma

Learn JavaScript and CSS
JavaScript and CSS resources

MediaWiki

The MediaWiki code base is large and some parts are ugly; don't be overwhelmed by it. When you're first starting off, aim to write features or fix bugs which only touch a small region of code.

MediaWiki basics and must-reads
MediaWiki resources

MediaWiki extensions

If you choose to work on MediaWiki extensions code, the following links provide more information.

MediaWiki extensions basics
MediaWiki extensions resources

See also