Warn when DISPLAYTITLE is used more than once

Implement the same duplicate-warning logic for DISPLAYTITLE that
DEFAULTSORT currently uses, to catch cases where a newer call overrides an
older one.

Bug: 50449
Change-Id: Ibce776d019aab07fb88fbb89afc5340300735405

includes/parser/CoreParserFunctions.php

@@ -365,9 +365,15 @@ class CoreParserFunctions {
 	 * @param string $text Desired title text
 	 * @return string
 	 */
-	static function displaytitle( $parser, $text = '' ) {
+	static function displaytitle( $parser, $text = '', $uarg = '' ) {
 		global $wgRestrictDisplayTitle;
 
+		static $magicWords = null;
+		if ( is_null( $magicWords ) ) {
+			$magicWords = new MagicWordArray( array( 'displaytitle_noerror', 'displaytitle_noreplace' ) );
+		}
+		$arg = $magicWords->matchStartToEnd( $uarg );
+
 		// parse a limited subset of wiki markup (just the single quote items)
 		$text = $parser->doQuotes( $text );
 
@@ -413,13 +419,25 @@ class CoreParserFunctions {
 		) );
 		$title = Title::newFromText( Sanitizer::stripAllTags( $text ) );
 
-		if ( !$wgRestrictDisplayTitle ) {
-			$parser->mOutput->setDisplayTitle( $text );
-		} elseif ( $title instanceof Title
+		if ( !$wgRestrictDisplayTitle ||
+			( $title instanceof Title
 			&& !$title->hasFragment()
-			&& $title->equals( $parser->mTitle )
+			&& $title->equals( $parser->mTitle ) )
 		) {
-			$parser->mOutput->setDisplayTitle( $text );
+			$old = $parser->mOutput->getProperty( 'displaytitle' );
+			if ( $old === false || $arg !== 'displaytitle_noreplace' ) {
+				$parser->mOutput->setDisplayTitle( $text );
+			}
+			if ( $old !== false && $old !== $text && !$arg ) {
+				$converter = $parser->getConverterLanguage()->getConverter();
+				return '<span class="error">' .
+					wfMessage( 'duplicate-displaytitle',
+						// Message should be parsed, but these params should only be escaped.
+						$converter->markNoConversion( wfEscapeWikiText( $old ) ),
+						$converter->markNoConversion( wfEscapeWikiText( $text ) )
+					)->inContentLanguage()->text() .
+					'</span>';
+			}
 		}
 
 		return '';

languages/i18n/en.json

@@ -3214,6 +3214,7 @@
 	"timezone-utc": "UTC",
 	"unknown_extension_tag": "Unknown extension tag \"$1\"",
 	"duplicate-defaultsort": "<strong>Warning:</strong> Default sort key \"$2\" overrides earlier default sort key \"$1\".",
+	"duplicate-displaytitle": "<strong>Warning:</strong> Display title \"$2\" overrides earlier display title \"$1\".",
 	"version": "Version",
 	"version-summary": "",
 	"version-extensions": "Installed extensions",

languages/i18n/qqq.json

@@ -3376,6 +3376,7 @@
 	"timezone-utc": "{{optional}}",
 	"unknown_extension_tag": "This is an error shown when you use an unknown extension tag name.\n\nThis feature allows tags like <code><nowiki><pre></nowiki></code> to be called with a parser like <code><nowiki>{{#tag:pre}}</nowiki></code>.\n\nParameters:\n* $1 - the unknown extension tag name",
 	"duplicate-defaultsort": "See definition of [[w:Sorting|sort key]] on Wikipedia. Parameters:\n* $1 - old default sort key\n* $2 - new default sort key",
+	"duplicate-displaytitle": "Warning shown when a page has its display title set multiple times. Parameters:\n* $1 - old display title\n* $2 - new display title",
 	"version": "{{doc-special|Version}}\n{{Identical|Version}}",
 	"version-summary": "{{doc-specialpagesummary|version}}",
 	"version-extensions": "Header on [[Special:Version]].",

languages/messages/MessagesEn.php

@@ -365,6 +365,8 @@ $magicWords = array(
 	'url_query'               => array( 0,    'QUERY' ),
 	'defaultsort_noerror'     => array( 0,    'noerror' ),
 	'defaultsort_noreplace'   => array( 0,    'noreplace' ),
+	'displaytitle_noerror'    => array( 0,    'noerror' ),
+	'displaytitle_noreplace'  => array( 0,    'noreplace' ),
 	'pagesincategory_all'     => array( 0,    'all' ),
 	'pagesincategory_pages'   => array( 0,    'pages' ),
 	'pagesincategory_subcats' => array( 0,    'subcats' ),