Index: src/wp-includes/capabilities.php
===================================================================
--- src/wp-includes/capabilities.php
+++ src/wp-includes/capabilities.php
@@ -1010,14 +1010,16 @@
 		 *
 		 * @since 2.0.0
 		 * @since 3.7.0 Added the user object.
+		 * @since ?     Added the $cap parameter.
 		 *
-		 * @param array   $allcaps An array of all the user's capabilities.
-		 * @param array   $caps    Actual capabilities for meta capability.
-		 * @param array   $args    Optional parameters passed to has_cap(), typically object ID.
-		 * @param WP_User $user    The user object.
+		 * @param array      $allcaps An array of all the user's capabilities.
+		 * @param array      $caps    Actual capabilities for meta capability.
+		 * @param array      $args    Optional parameters passed to has_cap(), typically object ID.
+		 * @param WP_User    $user    The user object.
+		 * @param string|int $cap     The capability or role name to search.
 		 */
 		// Must have ALL requested caps
-		$capabilities = apply_filters( 'user_has_cap', $this->allcaps, $caps, $args, $this );
+		$capabilities = apply_filters( 'user_has_cap', $this->allcaps, $caps, $args, $this, $cap );
 		$capabilities['exist'] = true; // Everyone is allowed to exist
 		foreach ( (array) $caps as $cap ) {
 			if ( empty( $capabilities[ $cap ] ) )