Extension:Scribunto

The Scribunto (Latin: "they shall write/let them write (in the future)") extension allows for embedding scripting languages in MediaWiki. Currently the only supported scripting language is Lua.

License
This extension contains code licensed GNU General Public License v2.0 or later (GPL-2.0+) as well as code licensed MIT License (MIT).

PCRE version compatibility
PCRE 8.33 or later is recommended. You can see the version of PCRE used by PHP by viewing a phpinfo web page, or from the command line with the command.


 * Scribunto will not work with versions of PCRE lower than 8.10.
 * PCRE 8.31 has bugs with JIT pattern studying that breaks various patterns when used with HHVM.
 * PCRE 8.32 has a bug that will cause it to reject certain non-character codepoints, which will cause errors in the mw.html module.

CentOS 6 and RHEL 6 are stuck on PCRE 7 and need to be upgraded.

Updating to 8.33 on a server with an older version may be relatively complicated. See Updating to PCRE 8.33 or Higher for details.

PHP pcntl
Since Scribunto for MediaWiki 1.25, your PHP server also needs to have pcntl enabled (only works with Unix/Linux platforms) if you want to use "LuaStandAlone" (i.e. running in a separate child process). Under Windows, Scribunto will run Lua only as "LuaSandbox" (within the same PHP thread as the thread used by MediaWiki to run this Scribunto extension, but within the sandboxing PHP environment configured by Scribunto).

This Linux command will output the line: 'pcntl support => enabled' if pcntl is enabled: php -i | grep 'pcntl support'

PHP mbstring extension
PHP needs to have the mbstring extension enabled.

To see if it installed on your server, you can check if it is enabled by running the command  on the server. If the string  is present in the output, the extension is enabled. ie: Linux command:  php -m | fgrep 'mbstring'

Bundled binaries
Scribunto comes bundled with Lua binary distributions for Linux (x86 and x86-64), Mac OS X Lion, and Windows (32- and 64-bit).

Scribunto should work for you out of the box if:
 * 1) Your web server is run on one of the above platforms.
 * 2) PHP's   function is not restricted
 * 3) Your web server is configured to allow the execution of binary files in the MediaWiki tree.
 * Execute permissions may need to be set; for example, in Linux use
 * If you are using SELinux in "Enforcing" mode on your server, you might need to set a proper context for the binaries. Example for RHEL/CentOS 7:

Additional binaries
Additional Lua binary distributions, which may be needed for your web server if its operating system is not in the list above, can be obtained from http://luabinaries.sourceforge.net/ or from your Linux distribution. Only binary files for Lua 5.1.x are supported. Once you've installed the appropriate binary file on your web server, configure the location of the file with:

Note that you should not add the above line unless you've confirmed that Scribunto's built-in binaries don't work for you.

Integrating extensions
For a more pleasant user interface, with syntax highlighting and a code editor with autoindent, install the following extensions:
 * Extension:WikiEditor
 * Extension:SyntaxHighlight
 * Extension:CodeEditor

Then in your LocalSettings.php after all the extension registrations, add:

LuaSandbox
We have developed a PHP extension written in C called LuaSandbox. It can be used as an alternative to the standalone binary, and will provide improved performance. See LuaSandbox for details and installation instructions.

If you initially installed the extension to use the Lua standalone binary, be sure to update LocalSettings.php with.

Configuration
The following configuration variables are available:
 * $wgScribuntoDefaultEngine : Select the engine. Valid values are the keys in $wgScribuntoEngineConf, which by default are 'luasandbox' or 'luastandalone'.
 * $wgScribuntoUseGeSHi : When Extension:SyntaxHighlight is installed, set this true to use it when displaying Module pages.
 * $wgScribuntoUseCodeEditor : When Extension:CodeEditor is installed, set this true to use it when editing Module pages.
 * $wgScribuntoEngineConf : An associative array for engine configuration. Keys are the valid values for $wgScribuntoDefaultEngine, and values are associative arrays of configuration data. Each configuration array must contain a 'class' key naming the ScribuntoEngineBase subclass to use.

Logging
Error output produced by the standalone interpreter are not logged by default. Configure logging with:

LuaStandalone
The following keys are used in $wgScribuntoEngineConf for Scribunto_LuaStandaloneEngine. Generally you'd set these as something like

$wgScribuntoEngineConf['luastandalone']['key'] = 'value';


 * luaPath : Specify the path to a Lua interpreter.
 * errorFile : Specify the path to a file, writable by the web server user, where the error and debugging output from the standalone interpreter will be logged.
 * memoryLimit : Specify the memory limit in bytes for the standalone interpreter on Linux (enforced using ulimit).
 * cpuLimit : Specify the CPU time limit in seconds for the standalone interpreter on Linux (enforced using ulimit).
 * allowEnvFuncs : Set true to allow use of setfenv and getfenv in modules.

LuaSandbox
The following keys are used in $wgScribuntoEngineConf for Scribunto_LuaSandboxEngine. Generally you'd set these as something like

$wgScribuntoEngineConf['luasandbox']['key'] = 'value';


 * memoryLimit : Specify the memory limit in bytes.
 * cpuLimit : Specify the CPU time limit in seconds.
 * profilerPeriod : Specify the time between polls in sections for the Lua profiler.
 * allowEnvFuncs : Set true to allow use of setfenv and getfenv in modules.

Usage
Scripts go in a new namespace called Module. Each module has a collection of functions, which can be called using wikitext syntax such as:

Learning Lua
Lua is a simple programming language intended to be accessible to beginners. For a quick crash-course on Lua, try Learn Lua in 15 Minutes.

The best comprehensive introduction to Lua is the book Programming in Lua. The first edition (for Lua 5.0) is available online and is mostly relevant to Lua 5.1, the version used by Scribunto:
 * Programming in Lua (scroll down past the book ads to find the text)

The reference manual is also useful:
 * Lua reference manual

Lua environment
In Lua, the set of all global variables and functions is called an environment.

Each call runs in a separate environment. Variables defined in one will not be available from another. This restriction was necessary to maintain flexibility in the wikitext parser implementation.

Troubleshooting
Note that red Lua error messages are clickable and will provide more detailed information.

Lua error: Internal error: The interpreter exited with status 1
When using the LuaStandalone engine (this is the default), errors along the lines of "Lua error: Internal error: The interpreter exited with status 1" may be generated if the standalone Lua interpreter cannot be executed or runs into various runtime errors. To obtain more information, assign a file path to. The interpreter's error output will be logged to the specified file, which should prove more helpful in tracking down the issue. The information in the debug log includes debugging information, which is why there is so much of it. You should be able to ignore any line beginning with "TX" or "RX".

Lua error: Internal error: The interpreter exited with status 2
When using the LuaStandalone engine (this is the default), status 2 suggests memory allocation errors, probably caused by settings that allocate inadequate memory space for PHP or lua, or both. Assigning a file path to  and examining that output can be valuable in diagnosing memory allocation errors.

Increase PHP allocation in your PHP configuration; add the line memory_limit = 200M. This allocation of 200MB is often sufficient (as of MediaWiki 1.24) but can be increased as required. Set Scribunto's memory allocation in LocalSettings.php as a line:

$wgScribuntoEngineConf['luastandalone']['memoryLimit'] = 209715200; # bytes

Finally, depending on the server configuration, some installations may be helped by adding another LocalSettings.php line

$wgMaxShellMemory = 204800; # in KB

Note that all 3 memory limits are given in different units.

Lua error: Internal error: The interpreter exited with status 24
When using the LuaStandalone engine (this is the default), status 24 suggests CPU time limit errors, although those should be generating a "The time allocated for running scripts has expired" message instead. It would be useful to file a task in Phabricator and participate in determining why the XCPU signal isn't being caught.

Lua error: Internal error: The interpreter exited with status 126
When using the LuaStandalone engine (this is the default), errors along the lines of "Lua error: Internal error: The interpreter exited with status 126" may be generated if the standalone Lua interpreter cannot be executed. This generally arises from either of 2 causes:
 * The lua executable file's permissions do not include Execute. Set permissions as described under.
 * The server does not allow execution of files from the place where the executable is installed, e.g. the filesystem is mounted with the 'noexec' flag. This often occurs with shared hosted servers. Remedies include adjusting  to point to a Lua 5.1 binary installed in an executable location, or adjusting or convincing the shared host to adjust the setting preventing execution.

Error condition such as: Fatal exception of type MWException
Check the MediaWiki, PHP, or webserver logs for more details on the exception, or temporarily set $wgShowExceptionDetails to true.

version `GLIBC_2.11' not found
If the above gives you errors such as "version `GLIBC_2.11' not found", it means the version of the standard C library on your system is too old for the binaries provided with Scribunto. You should upgrade your C library, or use a version of Lua 5.1 compiled for the C library you do have installed. To upgrade your C library, your best option is usually to follow your distribution's instructions for upgrading packages (or for upgrading to a new release of the distribution, if applicable).

If you copy the lua binaries from Scribunto master (or from 77905), that should suffice, if you can't or don't want to upgrade your C library. The distributed binaries were recently recompiled against an older version of glibc, so the minimum is now 2.3 rather than 2.11.

Lua errors in Scribunto files
Errors here include:
 * attempt to index field 'text' (a nil value)
 * Lua error in mw.html.lua at line 253: Invalid class given:

If you are getting errors such these when attempting to use modules imported from WMF wikis, most likely your version of Scribunto is out of date. Upgrade if possible; for advanced users, you might also try to identify the needed newer commits and cherry-pick them into your local installation.

preg_replace_callback: Compilation failed: unknown property name after \P or \p at offset 7

 * this usually indicates an incompatible version of PCRE; you’ll need to update to >= 8.10
 * @todo: link to instructions on how to upgrade

Lua error
If you copy templates from Wikipedia and then get big red "Lua error: x" messages where the Scribunto invocation (e.g. the template that uses ) should be, that probably means that you didn't import everything you needed. Make sure that you tick the "Include templates" box at w:Special:Export when you export.

When importing pages from another wiki, it is also possible for templates or modules in the imported data to overwrite existing templates or modules with the same title, which may break existing pages, templates, and modules that depend on the overwritten versions.

Blank screen
Make sure your extension version is applicable to your MediaWiki version.

Design documents

 * Linux.conf.au 2014 - Scribunto presentation.webm's presentation at linux.conf.au 2014 discussing the motivations, implementation challenges and results of deploying Scribunto and Lua.]]/Parser interface design/
 * /Victor's API proposal/
 * /Documentation specification/
 * /Tim's draft roadmap/

Other pages

 * /Deployment priorities/
 * /Brainstorming/
 * Lua scripting - Wikimedia activity page describing deployment plan to Wikimedia sites
 * /Lua reference manual/ - The reference about the Lua language, as well as its standard libraries and common Scribunto modules supported on Wikimedia sites
 * /Lua 5.2 changes/ - A list of known changes in Lua 5.2 that may cause code written in 5.1 to function unexpectedly
 * /Example modules/
 * /Example extension/ - Code for example extensions extending the Scribunto library.
 * /We use Lua/