Docs: Add documentation for $object_id, the optional second parameter in current_user_can() and WP_User::has_cap(), and the optional third parameter in map_meta_cap().

This change introduces the vernacular of "meta" vs "primitive" capabilities to core docs, and providing examples for each inline and attempts to make it clear that `$object_id` is really only useful if the passed `$capability` is of the meta cap variety.

Props jliman for the initial patch.
Fixes #32694.

Built from https://develop.svn.wordpress.org/trunk@34224


git-svn-id: http://core.svn.wordpress.org/trunk@34188 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/capabilities-functions.php

@@ -16,8 +16,12 @@
  *
  * @since 2.0.0
  *
- * @param string $cap Capability name.
- * @param int $user_id User ID.
+ * @param string $cap       Capability name.
+ * @param int    $user_id   User ID.
+ * @param int    $object_id Optional. ID of the specific object to check against if `$cap` is a "meta" cap.
+ *                          "Meta" capabilities, e.g. 'edit_post', 'edit_user', etc., are capabilities used
+ *                          by map_meta_cap() to map to other "primitive" capabilities, e.g. 'edit_posts',
+ *                          'edit_others_posts', etc. The parameter is accessed via func_get_args().
  * @return array Actual capabilities for meta capability.
  */
 function map_meta_cap( $cap, $user_id ) {
@@ -390,12 +394,24 @@ function map_meta_cap( $cap, $user_id ) {
 }
 
 /**
- * Whether current user has capability or role.
+ * Whether the current user has a specific capability.
+ *
+ * While checking against particular roles in place of a capability is supported
+ * in part, this practice is discouraged as it may produce unreliable results.
  *
  * @since 2.0.0
  *
- * @param string $capability Capability or role name.
- * @return bool
+ * @see WP_User::has_cap()
+ * @see map_meta_cap()
+ *
+ * @param string $capability Capability name.
+ * @param int    $object_id  Optional. ID of the specific object to check against if `$capability` is a "meta" cap.
+ *                           "Meta" capabilities, e.g. 'edit_post', 'edit_user', etc., are capabilities used
+ *                           by map_meta_cap() to map to other "primitive" capabilities, e.g. 'edit_posts',
+ *                           'edit_others_posts', etc. Accessed via func_get_args() and passed to WP_User::has_cap(),
+ *                           then map_meta_cap().
+ * @return bool Whether the current user has the given capability. If `$capability` is a meta cap and `$object_id` is
+ *              passed, whether the current user has the given meta capability for the given object.
  */
 function current_user_can( $capability ) {
 	$current_user = wp_get_current_user();

wp-includes/class-wp-user.php

@@ -634,15 +634,22 @@ class WP_User {
 	/**
 	 * Whether user has capability or role name.
 	 *
-	 * This is useful for looking up whether the user has a specific role
-	 * assigned to the user. The second optional parameter can also be used to
-	 * check for capabilities against a specific object, such as a post or user.
+	 * While checking against particular roles in place of a capability is supported
+	 * in part, this practice is discouraged as it may produce unreliable results.
 	 *
 	 * @since 2.0.0
 	 * @access public
 	 *
-	 * @param string|int $cap Capability or role name to search.
-	 * @return bool True, if user has capability; false, if user does not have capability.
+	 * @see map_meta_cap()
+	 *
+	 * @param string $cap       Capability name.
+	 * @param int    $object_id Optional. ID of the specific object to check against if `$cap` is a "meta" cap.
+	 *                          "Meta" capabilities, e.g. 'edit_post', 'edit_user', etc., are capabilities used
+	 *                          by map_meta_cap() to map to other "primitive" capabilities, e.g. 'edit_posts',
+	 *                          'edit_others_posts', etc. The parameter is accessed via func_get_args() and passed
+	 *                          to map_meta_cap().
+	 * @return bool Whether the current user has the given capability. If `$cap` is a meta cap and `$object_id` is
+	 *              passed, whether the current user has the given meta capability for the given object.
 	 */
 	public function has_cap( $cap ) {
 		if ( is_numeric( $cap ) ) {

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34223';
+$wp_version = '4.4-alpha-34224';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.