Stop expanding search term in <title> of the search results page

When entering a search term such as {{SITENAME}} on Special:Search,
the <title> was generated with template expansion.

This patch prevents transformation by using search term as rawParams
of the 'searchresults-title' and 'pagetitle' messages.

Change-Id: Ief0bdd10ad882ebfaeefd11bf4217e70dd922d9d

includes/specials/SpecialSearch.php

@@ -449,7 +449,9 @@ class SpecialSearch extends SpecialPage {
 		$out = $this->getOutput();
 		if( strval( $term ) !== ''  ) {
 			$out->setPageTitle( $this->msg( 'searchresults' ) );
-			$out->setHTMLTitle( $this->msg( 'pagetitle', $this->msg( 'searchresults-title', $term )->plain() ) );
+			$out->setHTMLTitle( $this->msg( 'pagetitle' )->rawParams(
+				$this->msg( 'searchresults-title' )->rawParams( $term )->text()
+			) );
 		}
 		// add javascript specific to special:search
 		$out->addModules( 'mediawiki.special.search' );

tests/phpunit/includes/specials/SpecialSearchTest.php

@@ -107,5 +107,38 @@ class SpecialSearchTest extends MediaWikiTestCase {
 		}
 		return $u;
 	}
+
+	/**
+	 * Verify we do not expand search term in <title> on search result page
+	 * https://gerrit.wikimedia.org/r/4841
+	 */
+	function testSearchTermIsNotExpanded() {
+
+		# Initialize [[Special::Search]]
+		$search = new SpecialSearch();
+		$search->getContext()->setTitle( Title::newFromText('Special:Search' ) );
+		$search->load();
+
+		# Simulate a user searching for a given term
+		$term = '{{SITENAME}}';
+		$search->showResults( $term );
+
+		# Lookup the HTML page title set for that page
+		$pageTitle = $search
+			->getContext()
+			->getOutput()
+			->getHTMLTitle();
+
+		# Craft the expected, plain, text:
+		$aPlainSearchTerm =
+			wfMessage( 'searchresults-title', $term )
+			->plain();
+
+		# Compare :-]
+		$this->assertStringStartsWith( $aPlainSearchTerm,
+			$pageTitle,
+			"Search term should not be expanded in Special:Search <title>"
+		);
+	}
 }