WatchedItemStore::setNotificationTimestampsForUser(): Allow clearing timestamp

ApiSetNotificationTimestamp expects to be able to clear the timestamp by
passing null. Allow that to work as expected.

Bug: T153482
Change-Id: Ibf4ba56f0abd3b72283f7a33e4665d5999a70b82

includes/WatchedItemStore.php

@@ -668,7 +668,7 @@ class WatchedItemStore implements StatsdAwareInterface {
 
 	/**
 	 * @param User $user The user to set the timestamp for
-	 * @param string $timestamp Set the update timestamp to this value
+	 * @param string|null $timestamp Set the update timestamp to this value
 	 * @param LinkTarget[] $targets List of targets to update. Default to all targets
 	 *
 	 * @return bool success
@@ -687,9 +687,13 @@ class WatchedItemStore implements StatsdAwareInterface {
 			$conds[] = $batch->constructSet( 'wl', $dbw );
 		}
 
+		if ( $timestamp !== null ) {
+			$timestamp = $dbw->timestamp( $timestamp );
+		}
+
 		$success = $dbw->update(
 			'watchlist',
-			[ 'wl_notificationtimestamp' => $dbw->timestamp( $timestamp ) ],
+			[ 'wl_notificationtimestamp' => $timestamp ],
 			$conds,
 			__METHOD__
 		);

tests/phpunit/includes/WatchedItemStoreUnitTest.php

@@ -2404,6 +2404,35 @@ class WatchedItemStoreUnitTest extends MediaWikiTestCase {
 		);
 	}
 
+	public function testSetNotificationTimestampsForUser_nullTimestamp() {
+		$user = $this->getMockNonAnonUserWithId( 1 );
+		$timestamp = null;
+
+		$mockDb = $this->getMockDb();
+		$mockDb->expects( $this->once() )
+			->method( 'update' )
+			->with(
+				'watchlist',
+				[ 'wl_notificationtimestamp' => null ],
+				[ 'wl_user' => 1 ]
+			)
+			->will( $this->returnValue( true ) );
+		$mockDb->expects( $this->exactly( 0 ) )
+			->method( 'timestamp' )
+			->will( $this->returnCallback( function( $value ) {
+				return 'TS' . $value . 'TS';
+			} ) );
+
+		$store = $this->newWatchedItemStore(
+			$this->getMockLoadBalancer( $mockDb ),
+			$this->getMockCache()
+		);
+
+		$this->assertTrue(
+			$store->setNotificationTimestampsForUser( $user, $timestamp )
+		);
+	}
+
 	public function testSetNotificationTimestampsForUser_specificTargets() {
 		$user = $this->getMockNonAnonUserWithId( 1 );
 		$timestamp = '20100101010101';