Variable to reference TOC numbers in MediaWiki

Question

MediaWiki auto generates numbers in the table of contents. Is there any way to reference these numbers from inside the sections? For example:

==Section==
==Section==
==Section==
===Sub-Section===
Here in {{VARIABLE}}, we talk about. . .

And have {{VARIABLE}} replaced with 3.1?

If you are familiar with LaTeX, I mean something like \ref{a_section}.

Answer 1

Here is one possible solution. It requires three files to be placed in [wiki_installation_dir]/extensions/GetSectionNumber/.

GetSectionNumber.php:

<?php

if ( !defined( 'MEDIAWIKI' ) ) {
    die( 'This file is an extension to MediaWiki and thus not a valid entry point.' );
}

$wgExtensionCredits['parserhook'][] = array(
    'path' => __FILE__,
    'name' => 'Get Section Number',
    'descriptionmsg' => 'Parser function to get the section number, given a title.',
    'version' => 0.8,
    'author' => 'Seamus J.',
    'url' => '',
);                                           

# Place this line in LocalSettings.php:
# require_once "$IP/extensions/GetSectionNumber/GetSectionNumber.php";

# This indicates where to find the localisation file. It is not optional.
$wgExtensionMessagesFiles['GetSectionNumber'] = __DIR__ . '/GetSectionNumber.i18n.php';

$wgAutoloadClasses['ExtGetSectionNumber'] = __DIR__ . '/GetSectionNumber_body.php';

# This indicates where in parser.php this code will run.
$wgHooks['ParserBeforeInternalParse'][] = 'ExtGetSectionNumber::onPBIParseDoFirst';
$wgHooks['ParserBeforeInternalParse'][] = 'ExtGetSectionNumber::onPBIParseDoSecond';

GetSectionNumber_body.php:

class ExtGetSectionNumber {

    static $numHeadings = 0;
    static $sectionNumber;
    private static $hasRun = false;

    # This function is called by the hook ParserBeforeInternalParse.
    # It registers the parser function that processes 'secnum'.
    public static function onPBIParseDoFirst( $parser ) {

        $parser->setFunctionHook( 'secnum', 'ExtGetSectionNumber::secnum' );
        return true;
    }

    # This function is called by the hook ParserBeforeInternalParse.
    # It parses the text to find the headlines and generate their numbering.
    public static function onPBIParseDoSecond( $parser, $text ) {
        if (self::$hasRun) return true;
        self::$hasRun = true;

        $matchArray = array();
        #global $sectionNumber;
        $sectionNumber = array();

        # Taken verbatim from doHeadings in parser.php
        # Replaces all '=' with the right <h> tags
        for ( $i = 6; $i >= 1; --$i ) {
            $h = str_repeat( '=', $i );
            $text = preg_replace( "/^$h(.+)$h\\s*$/m", "<h$i>\\1</h$i>", $text );
        }

        # Taken from formatHeadings in parser.php and modified a bit
        # \start generate numbers
        self::$numHeadings = preg_match_all(
            #'/tocnumber">(?<level>[\d\.]+)<[^<>]+>[\s]<[^<>]+>(?<heading>[^<]+)/',
            '/<H(?P<level>[1-6])(?:.*?>)\s*(?P<header>[\s\S]*?)\s*<\/H[1-6] *>/i',
            $text,
            $matchArray);
        # $headlines is an array of the headings on the wiki page
        $headlines = $numHeadings !== false ? $matchArray['header'] : array();
        # $headlineCount is an iterator used to access $matches
        $headlineCount = 0;
        # $level is the current level *according to* <hx> tags
        # initialize this to first level, so that we can skip special case in loop
        $level = $matchArray['level'][0]; 
        # $numberingArray[0-4] tracks the current level in actual numbers
        # it constructs the number string stored in $sectionNumbers
        $numberingArray = array();
        $numberingArray[0] = 0;
        # $depth tracks how much of $numberingArray is relevant at each level
        $depth = 0;

        foreach ( $headlines as $headline ) {
            # heading is a sibling to the last one
            if ( $matchArray['level'][$headlineCount] == $level ) {
                $numberingArray[$depth] += 1;
            }
            # heading is superior to the last one
            elseif ( $matchArray['level'][$headlineCount] < $level ) {
                $diff = $level - $matchArray['level'][$headlineCount];
                $level -= $diff;
                $depth -= $diff;
                $numberingArray[$depth] += 1;
            } 
            # heading is a subsection of the last one
            elseif ( $matchArray['level'][$headlineCount] > $level ) {
                $level += 1;
                $depth += 1;
                $numberingArray[$depth] = 1;
            }

            # generate the number
            for ($i = 0; $i <= $depth; $i++) {
                if ( $i === 0 ) { # we don't need a period at the start of the number
                    $sectionNumber[$headline][0] = $numberingArray[$i];
                } else {
                    $sectionNumber[$headline][0] .= '.' . $numberingArray[$i];
                }
            }

            # initialize the autoinc number to 1
            $sectionNumber[$headline][1] = 1;

            $headlineCount += 1;
        }
        # \end generate numbers

        # transfer the local array to a class static one
        # so we only need to run onPBIParseDoSecond once
        self::$sectionNumber = $sectionNumber;

        return true;
    }

    # This returns the formated number for the requested section heading.
    # It is also capable of formating auto-incrementing "sub" numbers for use in lists, etc.
    public static function secnum( $parser, $autoinc, $heading ) {

        # if the requested heading exists
        if (array_key_exists($heading,self::$sectionNumber)) {

            $autoinc = strtoupper($autoinc);

            if ($autoinc === 'Y' or $autoinc === 'YES') {
                $output = '<strong>' . self::$sectionNumber[$heading][0]
                    . '.' . self::$sectionNumber[$heading][1] . '</strong>';
                self::$sectionNumber[$heading][1]++; # increment for the next call
            } else {
                    $output = '<strong>' . self::$sectionNumber[$heading][0] . '</strong>';
                self::$sectionNumber[$heading][1] = 1; # reset the auto increment
            }

        } else {
            $output = '<strong>' . htmlspecialchars($heading) . '</strong>';
        }

        return $output;
    }
}

GetSectionNumber.i18n.php:

<?php

# Internationalization file for GetSectionNumber
# make sure  $wgExtensionMessageFiles['GetSectionNumber'] = __DIR__ . '/GetSectionNumber.i18n.php
# is placed in GetSectionNumber.php

$magicWords = array();

/** English (en) **/
$magicWords['en'] = array(
    'secnum' => array( 0, 'secnum' ),
);

Follow the instructions in the comments to install. To use, insert {{#secnum:$x|$T}} in the wiki code wherever you want the numbers to appear. $x is yes/YES/y/Y if you want to turn on auto-incrementing "sub" numbering (like if you are using this in a list, which is what I wanted it for) or N/n otherwise. $T is the heading title of the section, spelled and spaced exactly as it is between the ='s.