Hard-deprecate MWTimestamp::getHumanTimestamp

Originally deprecated in 1.26.

Depends-On: I9ae99887b11879ae0ef083acf93a791cf72eb2d0
Change-Id: Ifdfeb88f8998bd01a32df86952dd6e85451bf074

RELEASE-NOTES-1.39

@@ -355,6 +355,8 @@ because of Phabricator reports.
   - ::setUserObj() → ::setUsername()
   - ::setUserIP() → ::setUsername()
 * ObjectCache::addBusyCallback() is deprecated and non-functional.
+* MWTimestamp::getHumanTimestamp(), deprecated in 1.26, now emits deprecation
+  warnings.
 * …
 
 === Other changes in 1.39 ===

includes/MWTimestamp.php

@@ -68,6 +68,7 @@ class MWTimestamp extends ConvertibleTimestamp {
 	public function getHumanTimestamp(
 		MWTimestamp $relativeTo = null, UserIdentity $user = null, Language $lang = null
 	) {
+		wfDeprecated( __METHOD__, '1.26' );
 		if ( $lang === null ) {
 			$lang = RequestContext::getMain()->getLanguage();
 		}

tests/phpunit/includes/MWTimestampTest.php

@@ -38,6 +38,7 @@ class MWTimestampTest extends MediaWikiLangTestCase {
 		$expectedOutput, // The expected output
 		$desc // Description
 	) {
+		$this->hideDeprecated( 'MWTimestamp::getHumanTimestamp' );
 		$this->setMockUserOptions( [
 			'timecorrection' => $timeCorrection,
 			'date' => $dateFormat