s/existant/existent/

includes/EditPage.php

@@ -1781,7 +1781,7 @@ END
 
 	/**
 	 * Creates a basic error page which informs the user that
-	 * they have attempted to edit a nonexistant section.
+	 * they have attempted to edit a nonexistent section.
 	 */
 	function noSuchSectionPage() {
 		global $wgOut, $wgTitle;

includes/api/ApiLogin.php

@@ -44,7 +44,7 @@ class ApiLogin extends ApiBase {
 	 * Executes the log-in attempt using the parameters passed. If
 	 * the log-in succeeeds, it attaches a cookie to the session
 	 * and outputs the user id, username, and session token. If a
-	 * log-in fails, as the result of a bad password, a nonexistant
+	 * log-in fails, as the result of a bad password, a nonexistent
 	 * user, or any other reason, the host is cached with an expiry
 	 * and no log-in attempts will be accepted until that expiry
 	 * is reached. The expiry is $this->mLoginThrottle.

includes/api/ApiPageSet.php

@@ -426,7 +426,7 @@ class ApiPageSet extends ApiQueryBase {
 		if(isset($remaining)) {
 			// Any items left in the $remaining list are added as missing
 			if($processTitles) {
-				// The remaining titles in $remaining are non-existant pages
+				// The remaining titles in $remaining are non-existent pages
 				foreach ($remaining as $ns => $dbkeys) {
 					foreach ( $dbkeys as $dbkey => $unused ) {
 						$title = Title :: makeTitle($ns, $dbkey);

maintenance/parserTests.txt

@@ -2207,7 +2207,7 @@ PMID 1234
 ####
 
 !! test
-Nonexistant template
+Nonexistent template
 !! input
 {{thistemplatedoesnotexist}}
 !! result
@@ -2749,7 +2749,7 @@ PST
 !! end
 
 !! test
-pre-save transform: nonexistant template
+pre-save transform: nonexistent template
 !! options
 PST
 !! input