How to become a MediaWiki hacker

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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 a good first bug.

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

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

Overview

MediaWiki is the software that powers Wikipedia, its sister projects and thousands of wikis all over the world.

MediaWiki is written in the PHP programming language[1]. It uses jQuery as the client JavaScript library.

MediaWiki is primarily written for the LAMP platform[2] and runs on most operating systems. MediaWiki primarily uses the MySQL or MariaDB database servers.[3]

Development happens in an open source style[4], is largely coordinated online, and 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 (Docker or Vagrant), or a manual configuration approach.

Docker development environment

  • MediaWiki Docker – Run MediaWiki using Docker (can be used on Linux, Windows, or macOS hosts). This is the recommended method.

You can also try the experimental mwcli tool which provides basic orchestration functionality for MediaWiki docker containers.


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).

Vagrant is a powerful tool, but it is more complex and less robust than Docker, and significantly more resource-intensive. It is mainly aimed at developers who need to set up complex, flexible environments, e.g. for testing the interaction of multiple extensions.

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.

Communication tips and guidelines

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 Phabricator ).
  • Do your research first: When you decide to work on a task, 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 code changes. For a general overview, please read the Basics to know.
    • In a Phabricator task, see the project tags in the side bar to find out which code repository a task is about.
  • Ask and discuss in the best place:
    • In Phabricator tasks, discuss only specific questions about the topic of that very Phabricator task. General technical questions (e.g. how to set up a development environment or problems with Gerrit) are off-topic in Phabricator tasks.
    • For general technical questions, ask the broader Wikimedia community and use generic channels like IRC chat or mailing lists. (If you take part in an outreach program, then you can also use Zulip's technical-support stream.)
    • If you take part in an outreach program, then Zulip is for discussing questions about the outreach programs themselves.
  • Ask good questions: "Can you give me more info?", "Please guide me", "Please tell me how to start" are not good comments 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 – consider finding an easier one first.
  • Provide context: When asking, explain what you want to achieve, and 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. Use specific titles and subject lines ("Proposal draft" or "Need help" is not specific).
  • Use Inclusive language : Don't assume anyone's gender identity ("guys", "madam", "sir"). Use the name of the person instead.
  • Ask in public: Do not send private messages if your conversation topic is not secret. Private messages do not help others.
  • Be patient when seeking input and comments, especially during weekends and holidays.
    • 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 try again at a different time; don't just give up.
    • Do not ask people immediately for code review in a separate message. People receive Gerrit and Phabricator notifications.
  • Keep conversations readable: When you reply in Zulip, in Phabricator tasks, or on mailing lists, please avoid unneeded quoting of a complete previous comment. Provide sufficient context and keep threads readable.
  • Follow the code of conduct for Wikimedia technical spaces.
  • When you plan to work on a Phabricator task:
    • No need to ask for permission: Usually there is no reason to ask if you can work on something or if somebody could assign a task to you. There is no authority who assigns tasks or who needs to be asked first.
    • You do not need to announce your plans before you start working on a task but it would be welcome. At the latest when you are close to proposing a patch for a task, it is good to announce that you are working on it, so that others don't duplicate work: If nobody else is already assigned, set yourself as task assignee by using the Add Action… → Assign/Claim dropdown.
    • Tasks with existing patches:
      • If a task already has a recent patch in Gerrit, 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 improve that existing patch, based on the feedback in Gerrit and in the task.
    • When your plans or interests change: If you don't work on a task anymore, please 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 clearly and early you get 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.
  • Also, the script maintenance/shell.php in MediaWiki is a replacement of maintenance/eval.php based on PsySH, see Manual:Shell.php

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. You don't have to be familiar with JavaScript, jQuery and CSS to work on MediaWiki, but you might need to, depending on what you choose to work on.

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

  1. ↑ Not all of MediaWiki is written in PHP. Some supporting tools are written in other languages, including batch files, shell scripts, makefiles and Python.
  2. ↑ MediaWiki runs on most platforms that can support PHP, however, the lack of certain utilities or operating system features may limit the functionality or performance of MediaWiki on non-LAMP platforms.
  3. ↑ MediaWiki has support for DBMS other than MySQL and MariaDB, including PostgreSQL, SQLite
  4. ↑ Developers are a mix of volunteers and paid staff (or contractors) for various organizations. For a full list of who works on the MediaWiki code, read the Developers article.
  5. ↑ Browse the source code and revisions of code repositories at https://phabricator.wikimedia.org/diffusion/ or download the source code to your system by using Gerrit.
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