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.

Although MediaWiki is written in the PHP programming language, some supporting tools are written in other languages, including batch files, shell scripts, makefiles and Python. It uses jQuery as the client JavaScript library.

MediaWiki is primarily written for the LAMP platform[1] and runs on most operating systems. MediaWiki primarily uses the MySQL or MariaDB database servers.[2]

Development happens in an open source style[3], 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 ).

Follow these tips to communicate effectively and get help from community members.

Use Phabricator tasks effectively

When you plan to work on a Phabricator task:

  • No need to ask for permission: You can work on unassigned tasks without asking someone to assign them to you. There is no authority who assigns tasks or who needs to be asked first.
    • If a task already has a recent patch in Gerrit, choose a different task to work on instead.
    • If an existing patch in Gerrit has not been merged and has not seen any changes for a long time, you could improve that existing patch, based on the feedback in Gerrit and in the task.
  • Do your research: When you consider working on a task, do research before you start coding. Look at the code, try to understand what it is supposed to do, read related documentation, and try to find the places where you need to make code changes.
    • In a Phabricator task, use the project tags in the side bar to find the code repository for the task.
    • If you have no idea at all how to fix the bug, consider finding an easier one first.
  • You do not need to announce your plans before you start working on a task, but you should communicate that you are working on the task.
    • When you start work, set yourself as task assignee by clicking Edit Task… in Phabricator, and set your Phabricator username in the Assigned To field. This communicates to others that you are working on it, so they don't duplicate work.
    • When your plans or interests change: If you are no longer working on a task, remove yourself as the assignee of the task. This tells others that they can work on the task, and they won't expect you to still work on it.
  • Follow Phabricator etiquette.
    • In Phabricator tasks, discuss only specific questions about the topic of that task. Don't use Phabricator to ask general questions, like how to set up a development environment or how to fix problems with Gerrit.

Compose good questions

  • Don't ask to ask...just ask!.
  • Be specific and provide context: Instead of simply asking "Can you give me more info?", "Please guide me", or "Please tell me how to start", include the following information in your question:
    • What are you trying to achieve?
    • What have you already tried? Copy and paste your commands and their output (if not too long) instead of paraphrasing in your own words.
    • What have you found out already during your research? Include links to code, documentation, or other resources you already consulted.
  • Use specific titles and subject lines in your communication. "Proposal draft" or "Need help" is not specific.
  • Keep conversations readable: When you reply in Zulip, in Phabricator tasks, or on mailing lists, only quote sections of previous comments that are relevant to your response. If you quote a complete previous comment, it makes threads hard to read.

Follow communication policies and best practices

Before you send or post your question:

Ask in the right place

  • Ask in public: Do not send private messages if your conversation topic is not secret. Private messages don't help others.
  • Ask and discuss in the best place:
    • In Phabricator tasks, discuss only specific questions about the topic of that task.
    • Ask general technical questions, like how to set up a development environment or how to fix problems with Gerrit, in the places listed on Communication .
    • If you take part in an outreach program, then Zulip is for discussing questions about the outreach programs themselves.

Be patient

After you post your question:

  • Do not ask people for code review in a separate message. People receive Gerrit and Phabricator notifications and will respond when they can.
  • When seeking input and comments, especially during weekends and holidays, you may need to wait until business hours resume. On chat channels like IRC: if nobody answers, try again at a different time; don't just give up!
  • If you don't get an answer even after waiting and being patient, consider if other Communication channels might be a better place to ask your question.

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 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. ↑ 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.
  2. ↑ MediaWiki has support for DBMS other than MySQL and MariaDB, including PostgreSQL, SQLite
  3. ↑ 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.
  4. ↑ 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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