Ticket #38323: 38323.12.diff

src/wp-includes/capabilities.php

@@ -281 +281 @@
                         list( $_, $object_type, $_ ) = explode( '_', $cap );
                         $object_id                   = (int) $args[0];
 
-                        switch ( $object_type ) {
-                                case 'post':
-                                        $post = get_post( $object_id );
-                                        if ( ! $post ) {
-                                                break;
-                                        }
-
-                                        $sub_type = get_post_type( $post );
-                                        break;
-
-                                case 'comment':
-                                        $comment = get_comment( $object_id );
-                                        if ( ! $comment ) {
-                                                break;
-                                        }
-
-                                        $sub_type = empty( $comment->comment_type ) ? 'comment' : $comment->comment_type;
-                                        break;
-
-                                case 'term':
-                                        $term = get_term( $object_id );
-                                        if ( ! $term instanceof WP_Term ) {
-                                                break;
-                                        }
-
-                                        $sub_type = $term->taxonomy;
-                                        break;
+                        $object_subtype = get_object_subtype( $object_type, $object_id );
 
-                                case 'user':
-                                        $user = get_user_by( 'id', $object_id );
-                                        if ( ! $user ) {
-                                                break;
-                                        }
-
-                                        $sub_type = 'user';
-                                        break;
-                        }
-
-                        if ( empty( $sub_type ) ) {
+                        if ( empty( $object_subtype ) ) {
                                 $caps[] = 'do_not_allow';
                                 break;
                         }
@@ -328 +292 @@
 
                         $meta_key = isset( $args[1] ) ? $args[1] : false;
 
-                        $has_filter = has_filter( "auth_{$object_type}_meta_{$meta_key}" ) || has_filter( "auth_{$object_type}_{$sub_type}_meta_{$meta_key}" );
-                        if ( $meta_key && $has_filter ) {
-
-                                /**
-                                 * Filters whether the user is allowed to edit meta for specific object types.
-                                 *
-                                 * Return true to have the mapped meta caps from `edit_{$object_type}` apply.
-                                 *
-                                 * The dynamic portion of the hook name, `$object_type` refers to the object type being filtered.
-                                 * The dynamic portion of the hook name, `$meta_key`, refers to the meta key passed to map_meta_cap().
-                                 *
-                                 * @since 3.3.0 As `auth_post_meta_{$meta_key}`.
-                                 * @since 4.6.0
-                                 *
-                                 * @param bool     $allowed   Whether the user can add the object meta. Default false.
-                                 * @param string   $meta_key  The meta key.
-                                 * @param int      $object_id Object ID.
-                                 * @param int      $user_id   User ID.
-                                 * @param string   $cap       Capability name.
-                                 * @param string[] $caps      Array of the user's capabilities.
-                                 */
-                                $allowed = apply_filters( "auth_{$object_type}_meta_{$meta_key}", false, $meta_key, $object_id, $user_id, $cap, $caps );
-
-                                /**
-                                 * Filters whether the user is allowed to edit meta for specific object types/subtypes.
-                                 *
-                                 * Return true to have the mapped meta caps from `edit_{$object_type}` apply.
-                                 *
-                                 * The dynamic portion of the hook name, `$object_type` refers to the object type being filtered.
-                                 * The dynamic portion of the hook name, `$sub_type` refers to the object subtype being filtered.
-                                 * The dynamic portion of the hook name, `$meta_key`, refers to the meta key passed to map_meta_cap().
-                                 *
-                                 * @since 4.6.0 As `auth_post_{$post_type}_meta_{$meta_key}`.
-                                 * @since 4.7.0
-                                 *
-                                 * @param bool     $allowed   Whether the user can add the object meta. Default false.
-                                 * @param string   $meta_key  The meta key.
-                                 * @param int      $object_id Object ID.
-                                 * @param int      $user_id   User ID.
-                                 * @param string   $cap       Capability name.
-                                 * @param string[] $caps      Array of the user's capabilities.
-                                 */
-                                $allowed = apply_filters( "auth_{$object_type}_{$sub_type}_meta_{$meta_key}", $allowed, $meta_key, $object_id, $user_id, $cap, $caps );
+                        if ( $meta_key ) {
+                                $allowed = ! is_protected_meta( $meta_key, $object_type );
+
+                                if ( ! empty( $object_subtype ) && has_filter( "auth_{$object_type}_meta_{$meta_key}_for_{$object_subtype}" ) ) {
+
+                                        /**
+                                         * Filters whether the user is allowed to edit a specific meta key of a specific object type and subtype.
+                                         *
+                                         * The dynamic portions of the hook name, `$object_type`, `$meta_key`,
+                                         * and `$object_subtype`, refer to the metadata object type (comment, post, term or user),
+                                         * the meta key value, and the object subtype respectively.
+                                         *
+                                         * @since 5.0.0
+                                         *
+                                         * @param bool     $allowed   Whether the user can add the object meta. Default false.
+                                         * @param string   $meta_key  The meta key.
+                                         * @param int      $object_id Object ID.
+                                         * @param int      $user_id   User ID.
+                                         * @param string   $cap       Capability name.
+                                         * @param string[] $caps      Array of the user's capabilities.
+                                         */
+                                        $allowed = apply_filters( "auth_{$object_type}_meta_{$meta_key}_for_{$object_subtype}", $allowed, $meta_key, $object_id, $user_id, $cap, $caps );
+                                } else {
+
+                                        /**
+                                         * Filters whether the user is allowed to edit a specific meta key of a specific object type.
+                                         *
+                                         * Return true to have the mapped meta caps from `edit_{$object_type}` apply.
+                                         *
+                                         * The dynamic portion of the hook name, `$object_type` refers to the object type being filtered.
+                                         * The dynamic portion of the hook name, `$meta_key`, refers to the meta key passed to map_meta_cap().
+                                         *
+                                         * @since 3.3.0 As `auth_post_meta_{$meta_key}`.
+                                         * @since 4.6.0
+                                         *
+                                         * @param bool     $allowed   Whether the user can add the object meta. Default false.
+                                         * @param string   $meta_key  The meta key.
+                                         * @param int      $object_id Object ID.
+                                         * @param int      $user_id   User ID.
+                                         * @param string   $cap       Capability name.
+                                         * @param string[] $caps      Array of the user's capabilities.
+                                         */
+                                        $allowed = apply_filters( "auth_{$object_type}_meta_{$meta_key}", $allowed, $meta_key, $object_id, $user_id, $cap, $caps );
+                                }
+
+                                if ( ! empty( $object_subtype ) ) {
+
+                                        /**
+                                         * Filters whether the user is allowed to edit meta for specific object types/subtypes.
+                                         *
+                                         * Return true to have the mapped meta caps from `edit_{$object_type}` apply.
+                                         *
+                                         * The dynamic portion of the hook name, `$object_type` refers to the object type being filtered.
+                                         * The dynamic portion of the hook name, `$object_subtype` refers to the object subtype being filtered.
+                                         * The dynamic portion of the hook name, `$meta_key`, refers to the meta key passed to map_meta_cap().
+                                         *
+                                         * @since 4.6.0 As `auth_post_{$post_type}_meta_{$meta_key}`.
+                                         * @since 4.7.0
+                                         * @deprecated 5.0.0 Use `auth_{$object_type}_meta_{$meta_key}_for_{$object_subtype}`
+                                         *
+                                         * @param bool     $allowed   Whether the user can add the object meta. Default false.
+                                         * @param string   $meta_key  The meta key.
+                                         * @param int      $object_id Object ID.
+                                         * @param int      $user_id   User ID.
+                                         * @param string   $cap       Capability name.
+                                         * @param string[] $caps      Array of the user's capabilities.
+                                         */
+                                        $allowed = apply_filters_deprecated( "auth_{$object_type}_{$object_subtype}_meta_{$meta_key}", array( $allowed, $meta_key, $object_id, $user_id, $cap, $caps ), '5.0.0', "auth_{$object_type}_meta_{$meta_key}_for_{$object_subtype}" );
+                                }
 
                                 if ( ! $allowed ) {
                                         $caps[] = $cap;
                                 }
-                        } elseif ( $meta_key && is_protected_meta( $meta_key, $object_type ) ) {
-                                $caps[] = $cap;
                         }
                         break;
                 case 'edit_comment':

src/wp-includes/meta.php

@@ -44 +44 @@
                 return false;
         }
 
+        $meta_subtype = get_object_subtype( $meta_type, $object_id );
+
         $column = sanitize_key( $meta_type . '_id' );
 
         // expected_slashed ($meta_key)
         $meta_key   = wp_unslash( $meta_key );
         $meta_value = wp_unslash( $meta_value );
-        $meta_value = sanitize_meta( $meta_key, $meta_value, $meta_type );
+        $meta_value = sanitize_meta( $meta_key, $meta_value, $meta_type, $meta_subtype );
 
         /**
          * Filters whether to add metadata of a specific type.
@@ -165 +167 @@
                 return false;
         }
 
+        $meta_subtype = get_object_subtype( $meta_type, $object_id );
+
         $column    = sanitize_key( $meta_type . '_id' );
         $id_column = 'user' == $meta_type ? 'umeta_id' : 'meta_id';
 
@@ -173 +177 @@
         $meta_key     = wp_unslash( $meta_key );
         $passed_value = $meta_value;
         $meta_value   = wp_unslash( $meta_value );
-        $meta_value   = sanitize_meta( $meta_key, $meta_value, $meta_type );
+        $meta_value   = sanitize_meta( $meta_key, $meta_value, $meta_type, $meta_subtype );
 
         /**
          * Filters whether to update metadata of a specific type.
@@ -666 +670 @@
                         return false;
                 }
 
+                $meta_subtype = get_object_subtype( $meta_type, $object_id );
+
                 // Sanitize the meta
                 $_meta_value = $meta_value;
-                $meta_value  = sanitize_meta( $meta_key, $meta_value, $meta_type );
+                $meta_value  = sanitize_meta( $meta_key, $meta_value, $meta_type, $meta_subtype );
                 $meta_value  = maybe_serialize( $meta_value );
 
                 // Format the data query arguments.
@@ -968 +974 @@
  * Sanitize meta value.
  *
  * @since 3.1.3
+ * @since 5.0.0 The `$object_subtype` parameter was added.
  *
  * @param string $meta_key       Meta key.
  * @param mixed  $meta_value     Meta value to sanitize.
@@ -975 +982 @@
  *
  * @return mixed Sanitized $meta_value.
  */
-function sanitize_meta( $meta_key, $meta_value, $object_type ) {
+function sanitize_meta( $meta_key, $meta_value, $object_type, $object_subtype = '' ) {
+        if ( ! empty( $object_subtype ) && has_filter( "sanitize_{$object_type}_meta_{$meta_key}_for_{$object_subtype}" ) ) {
+
+                /**
+                 * Filters the sanitization of a specific meta key of a specific meta type and subtype.
+                 *
+                 * The dynamic portions of the hook name, `$object_type`, `$meta_key`,
+                 * and `$object_subtype`, refer to the metadata object type (comment, post, term or user),
+                 * the meta key value, and the object subtype respectively.
+                 *
+                 * @since 5.0.0
+                 *
+                 * @param mixed  $meta_value     Meta value to sanitize.
+                 * @param string $meta_key       Meta key.
+                 * @param string $object_type    Object type.
+                 * @param string $object_subtype Object subtype.
+                 */
+                return apply_filters( "sanitize_{$object_type}_meta_{$meta_key}_for_{$object_subtype}", $meta_value, $meta_key, $object_type, $object_subtype );
+        }
+
         /**
          * Filters the sanitization of a specific meta key of a specific meta type.
          *
@@ -995 +1021 @@
 /**
  * Registers a meta key.
  *
+ * It is recommended to register meta keys for a specific combination of object type and object subtype. If passing
+ * an object subtype is omitted, the meta key will be registered for the entire object type, however it can be partly
+ * overridden in case a more specific meta key of the same name exists for the same object type and a subtype.
+ *
+ * If an object type does not support any subtypes, such as users or comments, you should commonly call this function
+ * without passing a subtype.
+ *
  * @since 3.3.0
  * @since 4.6.0 {@link https://core.trac.wordpress.org/ticket/35658 Modified
  *              to support an array of data to attach to registered meta keys}. Previous arguments for
  *              `$sanitize_callback` and `$auth_callback` have been folded into this array.
+ * @since 5.0.0 The `$object_subtype` argument was added to the arguments array.
  *
  * @param string $object_type    Type of object this meta is registered to.
  * @param string $meta_key       Meta key to register.
  * @param array  $args {
  *     Data used to describe the meta key when registered.
  *
+ *     @type string $object_subtype    A subtype; e.g. if the object type is "post", the post type. If left empty,
+ *                                     the meta key will be registered on the entire object type. Default empty.
  *     @type string $type              The type of data associated with this meta key.
  *                                     Valid values are 'string', 'boolean', 'integer', and 'number'.
  *     @type string $description       A description of the data attached to this meta key.
@@ -1027 +1063 @@
         }
 
         $defaults = array(
+                'object_subtype'    => '',
                 'type'              => 'string',
                 'description'       => '',
                 'single'            => false,
@@ -1067 +1104 @@
         $args = apply_filters( 'register_meta_args', $args, $defaults, $object_type, $meta_key );
         $args = wp_parse_args( $args, $defaults );
 
+        $object_subtype = ! empty( $args['object_subtype'] ) ? $args['object_subtype'] : '';
+
         // If `auth_callback` is not provided, fall back to `is_protected_meta()`.
         if ( empty( $args['auth_callback'] ) ) {
                 if ( is_protected_meta( $meta_key, $object_type ) ) {
@@ -1078 +1117 @@
 
         // Back-compat: old sanitize and auth callbacks are applied to all of an object type.
         if ( is_callable( $args['sanitize_callback'] ) ) {
-                add_filter( "sanitize_{$object_type}_meta_{$meta_key}", $args['sanitize_callback'], 10, 3 );
+                if ( ! empty( $object_subtype ) ) {
+                        add_filter( "sanitize_{$object_type}_meta_{$meta_key}_for_{$object_subtype}", $args['sanitize_callback'], 10, 4 );
+                } else {
+                        add_filter( "sanitize_{$object_type}_meta_{$meta_key}", $args['sanitize_callback'], 10, 3 );
+                }
         }
 
         if ( is_callable( $args['auth_callback'] ) ) {
-                add_filter( "auth_{$object_type}_meta_{$meta_key}", $args['auth_callback'], 10, 6 );
+                if ( ! empty( $object_subtype ) ) {
+                        add_filter( "auth_{$object_type}_meta_{$meta_key}_for_{$object_subtype}", $args['auth_callback'], 10, 6 );
+                } else {
+                        add_filter( "auth_{$object_type}_meta_{$meta_key}", $args['auth_callback'], 10, 6 );
+                }
         }
 
         // Global registry only contains meta keys registered with the array of arguments added in 4.6.0.
         if ( ! $has_old_auth_cb && ! $has_old_sanitize_cb ) {
-                $wp_meta_keys[ $object_type ][ $meta_key ] = $args;
+                unset( $args['object_subtype'] );
+
+                $wp_meta_keys[ $object_type ][ $object_subtype ][ $meta_key ] = $args;
 
                 return true;
         }
@@ -1099 +1148 @@
  * Checks if a meta key is registered.
  *
  * @since 4.6.0
+ * @since 5.0.0 The `$object_subtype` parameter was added.
  *
  * @param string $object_type    The type of object.
  * @param string $meta_key       The meta key.
+ * @param string $object_subtype Optional. The subtype of the object type.
  *
- * @return bool True if the meta key is registered to the object type. False if not.
+ * @return bool True if the meta key is registered to the object type and, if provided,
+ *              the object subtype. False if not.
  */
-function registered_meta_key_exists( $object_type, $meta_key ) {
-        global $wp_meta_keys;
-
-        if ( ! is_array( $wp_meta_keys ) ) {
-                return false;
-        }
-
-        if ( ! isset( $wp_meta_keys[ $object_type ] ) ) {
-                return false;
-        }
-
-        if ( isset( $wp_meta_keys[ $object_type ][ $meta_key ] ) ) {
-                return true;
-        }
+function registered_meta_key_exists( $object_type, $meta_key, $object_subtype = '' ) {
+        $meta_keys = get_registered_meta_keys( $object_type, $object_subtype );
 
-        return false;
+        return isset( $meta_keys[ $meta_key ] );
 }
 
 /**
  * Unregisters a meta key from the list of registered keys.
  *
  * @since 4.6.0
+ * @since 5.0.0 The `$object_subtype` parameter was added.
  *
- * @param string $object_type The type of object.
- * @param string $meta_key    The meta key.
+ * @param string $object_type    The type of object.
+ * @param string $meta_key       The meta key.
+ * @param string $object_subtype Optional. The subtype of the object type.
  * @return bool True if successful. False if the meta key was not registered.
  */
-function unregister_meta_key( $object_type, $meta_key ) {
+function unregister_meta_key( $object_type, $meta_key, $object_subtype = '' ) {
         global $wp_meta_keys;
 
-        if ( ! registered_meta_key_exists( $object_type, $meta_key ) ) {
+        if ( ! registered_meta_key_exists( $object_type, $meta_key, $object_subtype ) ) {
                 return false;
         }
 
-        $args = $wp_meta_keys[ $object_type ][ $meta_key ];
+        $args = $wp_meta_keys[ $object_type ][ $object_subtype ][ $meta_key ];
 
         if ( isset( $args['sanitize_callback'] ) && is_callable( $args['sanitize_callback'] ) ) {
-                remove_filter( "sanitize_{$object_type}_meta_{$meta_key}", $args['sanitize_callback'] );
+                if ( ! empty( $object_subtype ) ) {
+                        remove_filter( "sanitize_{$object_type}_meta_{$meta_key}_for_{$object_subtype}", $args['sanitize_callback'] );
+                } else {
+                        remove_filter( "sanitize_{$object_type}_meta_{$meta_key}", $args['sanitize_callback'] );
+                }
         }
 
         if ( isset( $args['auth_callback'] ) && is_callable( $args['auth_callback'] ) ) {
-                remove_filter( "auth_{$object_type}_meta_{$meta_key}", $args['auth_callback'] );
+                if ( ! empty( $object_subtype ) ) {
+                        remove_filter( "auth_{$object_type}_meta_{$meta_key}_for_{$object_subtype}", $args['auth_callback'] );
+                } else {
+                        remove_filter( "auth_{$object_type}_meta_{$meta_key}", $args['auth_callback'] );
+                }
         }
 
-        unset( $wp_meta_keys[ $object_type ][ $meta_key ] );
+        unset( $wp_meta_keys[ $object_type ][ $object_subtype ][ $meta_key ] );
 
         // Do some clean up
+        if ( empty( $wp_meta_keys[ $object_type ][ $object_subtype ] ) ) {
+                unset( $wp_meta_keys[ $object_type ][ $object_subtype ] );
+        }
         if ( empty( $wp_meta_keys[ $object_type ] ) ) {
                 unset( $wp_meta_keys[ $object_type ] );
         }
@@ -1163 +1216 @@
  * Retrieves a list of registered meta keys for an object type.
  *
  * @since 4.6.0
+ * @since 5.0.0 The `$object_subtype` parameter was added.
  *
- * @param string $object_type The type of object. Post, comment, user, term.
+ * @param string $object_type    The type of object. Post, comment, user, term.
+ * @param string $object_subtype Optional. The subtype of the object type.
  * @return array List of registered meta keys.
  */
-function get_registered_meta_keys( $object_type ) {
+function get_registered_meta_keys( $object_type, $object_subtype = '' ) {
         global $wp_meta_keys;
 
-        if ( ! is_array( $wp_meta_keys ) || ! isset( $wp_meta_keys[ $object_type ] ) ) {
+        if ( ! is_array( $wp_meta_keys ) || ! isset( $wp_meta_keys[ $object_type ] ) || ! isset( $wp_meta_keys[ $object_type ][ $object_subtype ] ) ) {
                 return array();
         }
 
-        return $wp_meta_keys[ $object_type ];
+        return $wp_meta_keys[ $object_type ][ $object_subtype ];
 }
 
 /**
  * Retrieves registered metadata for a specified object.
  *
+ * The results include both meta that is registered specifically for the
+ * object's subtype and meta that is registered for the entire object type.
+ *
  * @since 4.6.0
  *
  * @param string $object_type Type of object to request metadata for. (e.g. comment, post, term, user)
@@ -1187 +1245 @@
  * @param string $meta_key    Optional. Registered metadata key. If not specified, retrieve all registered
  *                            metadata for the specified object.
  * @return mixed A single value or array of values for a key if specified. An array of all registered keys
- *               and values for an object ID if not.
+ *               and values for an object ID if not. False if a given $meta_key is not registered.
  */
 function get_registered_metadata( $object_type, $object_id, $meta_key = '' ) {
+        $object_subtype = get_object_subtype( $object_type, $object_id );
+
         if ( ! empty( $meta_key ) ) {
-                if ( ! registered_meta_key_exists( $object_type, $meta_key ) ) {
+                if ( ! empty( $object_subtype ) && ! registered_meta_key_exists( $object_type, $meta_key, $object_subtype ) ) {
+                        $object_subtype = '';
+                }
+
+                if ( ! registered_meta_key_exists( $object_type, $meta_key, $object_subtype ) ) {
                         return false;
                 }
-                $meta_keys     = get_registered_meta_keys( $object_type );
+
+                $meta_keys     = get_registered_meta_keys( $object_type, $object_subtype );
                 $meta_key_data = $meta_keys[ $meta_key ];
 
                 $data = get_metadata( $object_type, $object_id, $meta_key, $meta_key_data['single'] );
@@ -1203 +1268 @@
         }
 
         $data = get_metadata( $object_type, $object_id );
+        if ( ! $data ) {
+                return array();
+        }
 
-        $meta_keys       = get_registered_meta_keys( $object_type );
-        $registered_data = array();
-
-        // Someday, array_filter()
-        foreach ( $meta_keys as $k => $v ) {
-                if ( isset( $data[ $k ] ) ) {
-                        $registered_data[ $k ] = $data[ $k ];
-                }
+        $meta_keys = get_registered_meta_keys( $object_type );
+        if ( ! empty( $object_subtype ) ) {
+                $meta_keys = array_merge( $meta_keys, get_registered_meta_keys( $object_type, $object_subtype ) );
         }
 
-        return $registered_data;
+        return array_intersect_key( $data, $meta_keys );
 }
 
 /**
@@ -1223 +1286 @@
  * to be explicitly turned off is a warranty seal of sorts.
  *
  * @access private
- * @since  4.6.0
+ * @since 4.6.0
  *
- * @param  array $args         Arguments from `register_meta()`.
- * @param  array $default_args Default arguments for `register_meta()`.
+ * @param array $args         Arguments from `register_meta()`.
+ * @param array $default_args Default arguments for `register_meta()`.
  *
  * @return array Filtered arguments.
  */
 function _wp_register_meta_args_whitelist( $args, $default_args ) {
-        $whitelist = array_keys( $default_args );
+        return array_intersect_key( $args, $default_args );
+}
 
-        // In an anonymous function world, this would be better as an array_filter()
-        foreach ( $args as $key => $value ) {
-                if ( ! in_array( $key, $whitelist ) ) {
-                        unset( $args[ $key ] );
-                }
+/**
+ * Returns the object subtype for a given object ID of a specific type.
+ *
+ * @since 5.0.0
+ *
+ * @param string $object_type Type of object to request metadata for. (e.g. comment, post, term, user)
+ * @param int    $object_id   ID of the object to retrieve its subtype.
+ * @return string The object subtype or an empty string if unspecified subtype.
+ */
+function get_object_subtype( $object_type, $object_id ) {
+        $object_id      = (int) $object_id;
+        $object_subtype = '';
+
+        switch ( $object_type ) {
+                case 'post':
+                        $post_type = get_post_type( $object_type );
+
+                        if ( ! empty( $post_type ) ) {
+                                $object_subtype = $post_type;
+                        }
+                        break;
+
+                case 'term':
+                        $term = get_term( $object_id );
+                        if ( ! $term instanceof WP_Term ) {
+                                break;
+                        }
+
+                        $object_subtype = $term->taxonomy;
+                        break;
+
+                case 'comment':
+                        $comment = get_comment( $object_id );
+                        if ( ! $comment ) {
+                                break;
+                        }
+
+                        if ( ! empty( $comment->comment_type ) ) {
+                                $object_subtype = $comment->comment_type;
+                                break;
+                        }
+
+                        $object_subtype = 'comment';
+                        break;
+
+                case 'user':
+                        $user = get_user_by( 'id', $object_id );
+                        if ( ! $user ) {
+                                break;
+                        }
+
+                        $object_subtype = 'user';
+                        break;
         }
 
-        return $args;
+        /**
+         * Filters the object subtype identifier for a non standard object type.
+         *
+         * The dynamic portion of the hook, `$object_type`, refers to the object
+         * type (post, comment, term, or user).
+         *
+         * @since 5.0.0
+         *
+         * @param string $object_subtype Empty string to override.
+         * @param int    $object_id      ID of the object to get the subtype for.
+         */
+        return apply_filters( "get_object_subtype_{$object_type}", $object_subtype, $object_id );
 }

src/wp-includes/post.php

@@ -1989 +1989 @@
         return $deleted;
 }
 
+/**
+ * Registers a meta key for posts.
+ *
+ * @since 5.0.0
+ *
+ * @param string $post_type Post type to register a meta key for. Pass an empty string
+ *                          to register the meta key across all existing post types.
+ * @param string $meta_key  The meta key to register.
+ * @param array  $args      Data used to describe the meta key when registered. See
+ *                          {@see register_meta()} for a list of supported arguments.
+ * @return bool True if the meta key was successfully registered, false if not.
+ */
+function register_post_meta( $post_type, $meta_key, array $args ) {
+        $args['object_subtype'] = $post_type;
+
+        return register_meta( 'post', $meta_key, $args );
+}
+
+/**
+ * Unregisters a meta key for posts.
+ *
+ * @since 5.0.0
+ *
+ * @param string $post_type Post type the meta key is currently registered for. Pass
+ *                          an empty string if the meta key is registered across all
+ *                          existing post types.
+ * @param string $meta_key  The meta key to unregister.
+ * @return bool True on success, false if the meta key was not previously registered.
+ */
+function unregister_post_meta( $post_type, $meta_key ) {
+        return unregister_meta_key( 'post', $meta_key, $post_type );
+}
+
 /**
  * Retrieve post meta fields, based on post ID.
  *

src/wp-includes/rest-api/fields/class-wp-rest-comment-meta-fields.php

@@ -27 +27 @@
                 return 'comment';
         }
 
+        /**
+         * Retrieves the object meta subtype.
+         *
+         * @since 5.0.0
+         *
+         * @return string 'comment' There are no subtypes.
+         */
+        protected function get_meta_subtype() {
+                return 'comment';
+        }
+
         /**
          * Retrieves the type for register_rest_field() in the context of comments.
          *

src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php

@@ -24 +24 @@
          */
         abstract protected function get_meta_type();
 
+        /**
+         * Retrieves the object meta subtype.
+         *
+         * @since 5.0.0
+         *
+         * @return string Subtype for the meta type, or empty string if no specific subtype.
+         */
+        protected function get_meta_subtype() {
+                return '';
+        }
+
         /**
          * Retrieves the object type for register_rest_field().
          *
@@ -340 +351 @@
         protected function get_registered_fields() {
                 $registered = array();
 
-                foreach ( get_registered_meta_keys( $this->get_meta_type() ) as $name => $args ) {
+                $meta_type    = $this->get_meta_type();
+                $meta_subtype = $this->get_meta_subtype();
+
+                $meta_keys = get_registered_meta_keys( $meta_type );
+                if ( ! empty( $meta_subtype ) ) {
+                        $meta_keys = array_merge( $meta_keys, get_registered_meta_keys( $meta_type, $meta_subtype ) );
+                }
+
+                foreach ( $meta_keys as $name => $args ) {
                         if ( empty( $args['show_in_rest'] ) ) {
                                 continue;
                         }

src/wp-includes/rest-api/fields/class-wp-rest-post-meta-fields.php

@@ -46 +46 @@
                 return 'post';
         }
 
+        /**
+         * Retrieves the object meta subtype.
+         *
+         * @since 5.0.0
+         *
+         * @return string Subtype for the meta type, or empty string if no specific subtype.
+         */
+        protected function get_meta_subtype() {
+                return $this->post_type;
+        }
+
         /**
          * Retrieves the type for register_rest_field().
          *

src/wp-includes/rest-api/fields/class-wp-rest-term-meta-fields.php

@@ -46 +46 @@
                 return 'term';
         }
 
+        /**
+         * Retrieves the object meta subtype.
+         *
+         * @since 5.0.0
+         *
+         * @return string Subtype for the meta type, or empty string if no specific subtype.
+         */
+        protected function get_meta_subtype() {
+                return $this->taxonomy;
+        }
+
         /**
          * Retrieves the type for register_rest_field().
          *

src/wp-includes/rest-api/fields/class-wp-rest-user-meta-fields.php

@@ -27 +27 @@
                 return 'user';
         }
 
+        /**
+         * Retrieves the object meta subtype.
+         *
+         * @since 5.0.0
+         *
+         * @return string 'user' There are no subtypes.
+         */
+        protected function get_meta_subtype() {
+                return 'user';
+        }
+
         /**
          * Retrieves the type for register_rest_field().
          *

src/wp-includes/taxonomy.php

@@ -1322 +1322 @@
         return $wpdb->get_results( $wpdb->prepare( "SELECT meta_key, meta_value, meta_id, term_id FROM $wpdb->termmeta WHERE term_id = %d ORDER BY meta_key,meta_id", $term_id ), ARRAY_A );
 }
 
+/**
+ * Registers a meta key for terms.
+ *
+ * @since 5.0.0
+ *
+ * @param string $taxonomy Taxonomy to register a meta key for. Pass an empty string
+ *                         to register the meta key across all existing taxonomies.
+ * @param string $meta_key The meta key to register.
+ * @param array  $args     Data used to describe the meta key when registered. See
+ *                         {@see register_meta()} for a list of supported arguments.
+ * @return bool True if the meta key was successfully registered, false if not.
+ */
+function register_term_meta( $taxonomy, $meta_key, array $args ) {
+        $args['object_subtype'] = $taxonomy;
+
+        return register_meta( 'term', $meta_key, $args );
+}
+
+/**
+ * Unregisters a meta key for terms.
+ *
+ * @since 5.0.0
+ *
+ * @param string $taxonomy Taxonomy the meta key is currently registered for. Pass
+ *                         an empty string if the meta key is registered across all
+ *                         existing taxonomies.
+ * @param string $meta_key The meta key to unregister.
+ * @return bool True on success, false if the meta key was not previously registered.
+ */
+function unregister_term_meta( $taxonomy, $meta_key ) {
+        return unregister_meta_key( 'term', $meta_key, $taxonomy );
+}
+
 /**
  * Determines whether a term exists.
  *

tests/phpunit/tests/meta/registerMeta.php

@@ -3 +3 @@
  * @group meta
  */
 class Tests_Meta_Register_Meta extends WP_UnitTestCase {
+
         protected static $post_id;
+        protected static $term_id;
+        protected static $comment_id;
+        protected static $user_id;
 
         public static function wpSetUpBeforeClass( $factory ) {
-                self::$post_id = $factory->post->create();
+                self::$post_id    = $factory->post->create( array( 'post_type' => 'page' ) );
+                self::$term_id    = $factory->term->create( array( 'taxonomy' => 'category' ) );
+                self::$comment_id = $factory->comment->create();
+                self::$user_id    = $factory->user->create();
+        }
+
+        public static function wpTearDownAfterClass() {
+                wp_delete_post( self::$post_id, true );
+                wp_delete_term( self::$term_id, 'category' );
+                wp_delete_comment( self::$comment_id, true );
+                self::delete_user( self::$user_id );
         }
 
         public function _old_sanitize_meta_cb( $meta_value, $meta_key, $meta_type ) {
@@ -74 +88 @@
 
                 $expected = array(
                         'post' => array(
-                                'flight_number' => array(
-                                        'type'              => 'string',
-                                        'description'       => '',
-                                        'single'            => false,
-                                        'sanitize_callback' => null,
-                                        'auth_callback'     => '__return_true',
-                                        'show_in_rest'      => false,
+                                '' => array(
+                                        'flight_number' => array(
+                                                'type'              => 'string',
+                                                'description'       => '',
+                                                'single'            => false,
+                                                'sanitize_callback' => null,
+                                                'auth_callback'     => '__return_true',
+                                                'show_in_rest'      => false,
+                                        ),
                                 ),
                         ),
                 );
 
-                $this->assertEquals( $actual, $expected );
+                $this->assertEquals( $expected, $actual );
         }
 
         public function test_register_meta_with_term_object_type_populates_wp_meta_keys() {
@@ -96 +112 @@
 
                 $expected = array(
                         'term' => array(
-                                'category_icon' => array(
-                                        'type'              => 'string',
-                                        'description'       => '',
-                                        'single'            => false,
-                                        'sanitize_callback' => null,
-                                        'auth_callback'     => '__return_true',
-                                        'show_in_rest'      => false,
+                                '' => array(
+                                        'category_icon' => array(
+                                                'type'              => 'string',
+                                                'description'       => '',
+                                                'single'            => false,
+                                                'sanitize_callback' => null,
+                                                'auth_callback'     => '__return_true',
+                                                'show_in_rest'      => false,
+                                        ),
                                 ),
                         ),
                 );
 
-                $this->assertEquals( $actual, $expected );
+                $this->assertEquals( $expected, $actual );
         }
 
         public function test_register_meta_with_deprecated_sanitize_callback_does_not_populate_wp_meta_keys() {
@@ -148 +166 @@
 
                 $expected = array(
                         'post' => array(
-                                'flight_number' => array(
-                                        'type'              => 'string',
-                                        'description'       => '',
-                                        'single'            => false,
-                                        'sanitize_callback' => array( $this, '_new_sanitize_meta_cb' ),
-                                        'auth_callback'     => '__return_true',
-                                        'show_in_rest'      => false,
+                                '' => array(
+                                        'flight_number' => array(
+                                                'type'              => 'string',
+                                                'description'       => '',
+                                                'single'            => false,
+                                                'sanitize_callback' => array( $this, '_new_sanitize_meta_cb' ),
+                                                'auth_callback'     => '__return_true',
+                                                'show_in_rest'      => false,
+                                        ),
                                 ),
                         ),
                 );
@@ -301 +321 @@
 
                 $this->assertEmpty( $meta );
         }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_get_types_and_subtypes
+         */
+        public function test_register_meta_with_subtype_populates_wp_meta_keys( $type, $subtype ) {
+                global $wp_meta_keys;
+
+                register_meta( $type, 'flight_number', array( 'object_subtype' => $subtype ) );
+
+                $expected = array(
+                        $type => array(
+                                $subtype => array(
+                                        'flight_number' => array(
+                                                'type'              => 'string',
+                                                'description'       => '',
+                                                'single'            => false,
+                                                'sanitize_callback' => null,
+                                                'auth_callback'     => '__return_true',
+                                                'show_in_rest'      => false,
+                                        ),
+                                ),
+                        ),
+                );
+
+                $actual = $wp_meta_keys;
+
+                // Reset global so subsequent data tests do not get polluted.
+                $wp_meta_keys = array();
+
+                $this->assertEquals( $expected, $actual );
+        }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_get_types_and_subtypes
+         */
+        public function test_unregister_meta_with_subtype_unpopulates_wp_meta_keys( $type, $subtype ) {
+                global $wp_meta_keys;
+
+                register_meta( $type, 'flight_number', array( 'object_subtype' => $subtype ) );
+                unregister_meta_key( $type, 'flight_number', $subtype );
+
+                $actual = $wp_meta_keys;
+
+                // Reset global so subsequent data tests do not get polluted.
+                $wp_meta_keys = array();
+
+                $this->assertEmpty( $actual );
+        }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_get_types_and_subtypes
+         */
+        public function test_unregister_meta_without_subtype_keeps_subtype_meta_key( $type, $subtype ) {
+                global $wp_meta_keys;
+
+                register_meta( $type, 'flight_number', array( 'object_subtype' => $subtype ) );
+
+                // Unregister meta key without subtype.
+                unregister_meta_key( $type, 'flight_number' );
+
+                $expected = array(
+                        $type => array(
+                                $subtype => array(
+                                        'flight_number' => array(
+                                                'type'              => 'string',
+                                                'description'       => '',
+                                                'single'            => false,
+                                                'sanitize_callback' => null,
+                                                'auth_callback'     => '__return_true',
+                                                'show_in_rest'      => false,
+                                        ),
+                                ),
+                        ),
+                );
+
+                $actual = $wp_meta_keys;
+
+                // Reset global so subsequent data tests do not get polluted.
+                $wp_meta_keys = array();
+
+                $this->assertEquals( $expected, $actual );
+        }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_get_types_and_subtypes
+         */
+        public function test_get_registered_meta_keys_with_subtype( $type, $subtype ) {
+                register_meta( $type, 'registered_key1', array( 'object_subtype' => $subtype ) );
+                register_meta( $type, 'registered_key2', array( 'object_subtype' => $subtype ) );
+
+                $meta_keys = get_registered_meta_keys( $type, $subtype );
+
+                $this->assertArrayHasKey( 'registered_key1', $meta_keys );
+                $this->assertArrayHasKey( 'registered_key2', $meta_keys );
+                $this->assertEmpty( get_registered_meta_keys( $type ) );
+        }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_get_types_and_subtypes
+         */
+        public function test_get_registered_metadata_with_subtype( $type, $subtype ) {
+                register_meta( $type, 'registered_key1', array() );
+
+                // This will override the above registration for objects of $subtype.
+                register_meta( $type, 'registered_key1', array(
+                        'object_subtype' => $subtype,
+                        'single'         => true,
+                ) );
+
+                // For testing with $single => false.
+                register_meta( $type, 'registered_key2', array(
+                        'object_subtype' => $subtype,
+                ) );
+
+                // Register another meta key for a different subtype.
+                register_meta( $type, 'registered_key3', array(
+                        'object_subtype' => 'other_subtype',
+                ) );
+
+                $object_property_name = $type . '_id';
+                $object_id = self::$$object_property_name;
+
+                add_metadata( $type, $object_id, 'registered_key1', 'value1' );
+                add_metadata( $type, $object_id, 'registered_key2', 'value2' );
+                add_metadata( $type, $object_id, 'registered_key3', 'value3' );
+
+                $meta = get_registered_metadata( $type, $object_id );
+
+                $key1 = get_registered_metadata( $type, $object_id, 'registered_key1' );
+                $key2 = get_registered_metadata( $type, $object_id, 'registered_key2' );
+                $key3 = get_registered_metadata( $type, $object_id, 'registered_key3' );
+
+                $this->assertSame( array( 'registered_key1', 'registered_key2' ), array_keys( $meta ) );
+                $this->assertSame( 'value1', $meta['registered_key1'][0] );
+                $this->assertSame( 'value2', $meta['registered_key2'][0] );
+
+                $this->assertSame( 'value1', $key1 );
+                $this->assertSame( array( 'value2' ), $key2 );
+                $this->assertFalse( $key3 );
+        }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_get_types_and_subtypes
+         */
+        public function test_get_object_subtype( $type, $expected_subtype ) {
+                $object_property_name = $type . '_id';
+                $object_id = self::$$object_property_name;
+
+                $this->assertSame( $expected_subtype, get_object_subtype( $type, $object_id ) );
+        }
+
+        /**
+         * @ticket 38323
+         */
+        public function test_get_object_subtype_custom() {
+                add_filter( 'get_object_subtype_customtype', array( $this, 'filter_get_object_subtype_for_customtype' ), 10, 2 );
+
+                $subtype_for_3 = get_object_subtype( 'customtype', 3 );
+                $subtype_for_4 = get_object_subtype( 'customtype', 4 );
+
+                $this->assertSame( 'odd', $subtype_for_3 );
+                $this->assertSame( 'even', $subtype_for_4 );
+        }
+
+        public function filter_get_object_subtype_for_customtype( $subtype, $object_id ) {
+                if ( $object_id % 2 === 1 ) {
+                        return 'odd';
+                }
+
+                return 'even';
+        }
+
+        public function data_get_types_and_subtypes() {
+                return array(
+                        array( 'post', 'page' ),
+                        array( 'term', 'category' ),
+                        array( 'comment', 'comment' ),
+                        array( 'user', 'user' ),
+                );
+        }
 }

tests/phpunit/tests/post/meta.php

@@ -6 +6 @@
  */
 class Tests_Post_Meta extends WP_UnitTestCase {
 
+        private $last_register_meta_call = array(
+                'object_type' => '',
+                'meta_key'    => '',
+                'args'        => array(),
+        );
+
         protected static $author;
         protected static $post_id;
         protected static $post_id_2;
@@ -238 +244 @@
                 $this->assertEquals( $funky_meta, get_post_meta( self::$post_id, 'test_funky_post_meta', true ) );
 
         }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_register_post_meta
+         */
+        public function test_register_post_meta( $post_type, $meta_key, $args ) {
+                add_filter( 'register_meta_args', array( $this, 'filter_register_meta_args_set_last_register_meta_call' ), 10, 4 );
+
+                register_post_meta( $post_type, $meta_key, $args );
+
+                $args['object_subtype'] = $post_type;
+
+                // Reset global so subsequent data tests do not get polluted.
+                $GLOBALS['wp_meta_keys'] = array();
+
+                $this->assertEquals( 'post', $this->last_register_meta_call['object_type'] );
+                $this->assertEquals( $meta_key, $this->last_register_meta_call['meta_key'] );
+                $this->assertEquals( $args, $this->last_register_meta_call['args'] );
+        }
+
+        public function data_register_post_meta() {
+                return array(
+                        array( 'post', 'registered_key1', array( 'single' => true ) ),
+                        array( 'page', 'registered_key2', array() ),
+                        array( '', 'registered_key3', array( 'sanitize_callback' => 'absint' ) ),
+                );
+        }
+
+        public function filter_register_meta_args_set_last_register_meta_call( $args, $defaults, $object_type, $meta_key ) {
+                $this->last_register_meta_call['object_type'] = $object_type;
+                $this->last_register_meta_call['meta_key']    = $meta_key;
+                $this->last_register_meta_call['args']        = $args;
+
+                return $args;
+        }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_unregister_post_meta
+         */
+        public function test_unregister_post_meta( $post_type, $meta_key ) {
+                global $wp_meta_keys;
+
+                register_post_meta( $post_type, $meta_key, array() );
+                unregister_post_meta( $post_type, $meta_key );
+
+                $actual = $wp_meta_keys;
+
+                // Reset global so subsequent data tests do not get polluted.
+                $wp_meta_keys = array();
+
+                $this->assertEmpty( $actual );
+        }
+
+        public function data_unregister_post_meta() {
+                return array(
+                        array( 'post', 'registered_key1' ),
+                        array( 'page', 'registered_key2' ),
+                        array( '', 'registered_key3' ),
+                );
+        }
 }

tests/phpunit/tests/rest-api/rest-post-meta-fields.php

@@ -12 +12 @@
 class WP_Test_REST_Post_Meta_Fields extends WP_Test_REST_TestCase {
         protected static $wp_meta_keys_saved;
         protected static $post_id;
+        protected static $cpt_post_id;
 
         public static function wpSetUpBeforeClass( $factory ) {
+                register_post_type( 'cpt', array(
+                        'show_in_rest' => true,
+                        'supports'     => array( 'custom-fields' ),
+                ) );
+
                 self::$wp_meta_keys_saved = isset( $GLOBALS['wp_meta_keys'] ) ? $GLOBALS['wp_meta_keys'] : array();
                 self::$post_id            = $factory->post->create();
+                self::$cpt_post_id        = $factory->post->create( array( 'post_type' => 'cpt' ) );
         }
 
         public static function wpTearDownAfterClass() {
                 $GLOBALS['wp_meta_keys'] = self::$wp_meta_keys_saved;
                 wp_delete_post( self::$post_id, true );
+                wp_delete_post( self::$cpt_post_id, true );
+
+                unregister_post_type( 'cpt' );
         }
 
         public function setUp() {
@@ -120 +130 @@
                         )
                 );
 
+                register_post_type( 'cpt', array(
+                        'show_in_rest' => true,
+                        'supports'     => array( 'custom-fields' ),
+                ) );
+
+                register_post_meta( 'cpt', 'test_cpt_single', array(
+                        'show_in_rest'   => true,
+                        'single'         => true,
+                ) );
+
+                register_post_meta( 'cpt', 'test_cpt_multi', array(
+                        'show_in_rest'   => true,
+                        'single'         => false,
+                ) );
+
+                // Register 'test_single' on subtype to override for bad auth.
+                register_post_meta( 'cpt', 'test_single', array(
+                        'show_in_rest'   => true,
+                        'single'         => true,
+                        'auth_callback'  => '__return_false',
+                ) );
+
                 /** @var WP_REST_Server $wp_rest_server */
                 global $wp_rest_server;
                 $wp_rest_server = new Spy_REST_Server;
@@ -1047 +1079 @@
                 $this->assertArrayNotHasKey( 'test_no_type', $meta_schema );
         }
 
+        /**
+         * @ticket 38323
+         * @dataProvider data_get_subtype_meta_value
+         */
+        public function test_get_subtype_meta_value( $post_type, $meta_key, $single, $in_post_type ) {
+                $post_id  = self::$post_id;
+                $endpoint = 'posts';
+                if ( 'cpt' === $post_type ) {
+                        $post_id  = self::$cpt_post_id;
+                        $endpoint = 'cpt';
+                }
+
+                $meta_value = 'testvalue';
+
+                add_post_meta( $post_id, $meta_key, $meta_value );
+
+                $request = new WP_REST_Request( 'GET', sprintf( '/wp/v2/%s/%d', $endpoint, $post_id ) );
+                $response = rest_get_server()->dispatch( $request );
+
+                $this->assertEquals( 200, $response->get_status() );
+
+                $data = $response->get_data();
+
+                $this->assertArrayHasKey( 'meta', $data );
+                $this->assertInternalType( 'array', $data['meta'] );
+
+                if ( $in_post_type ) {
+                        $expected_value = $meta_value;
+                        if ( ! $single ) {
+                                $expected_value = array( $expected_value );
+                        }
+
+                        $this->assertArrayHasKey( $meta_key, $data['meta'] );
+                        $this->assertEquals( $expected_value, $data['meta'][ $meta_key ] );
+                } else {
+                        $this->assertArrayNotHasKey( $meta_key, $data['meta'] );
+                }
+        }
+
+        public function data_get_subtype_meta_value() {
+                return array(
+                        array( 'cpt', 'test_cpt_single', true, true ),
+                        array( 'cpt', 'test_cpt_multi', false, true ),
+                        array( 'cpt', 'test_single', true, true ),
+                        array( 'cpt', 'test_multi', false, true ),
+                        array( 'post', 'test_cpt_single', true, false ),
+                        array( 'post', 'test_cpt_multi', false, false ),
+                        array( 'post', 'test_single', true, true ),
+                        array( 'post', 'test_multi', false, true ),
+                );
+        }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_set_subtype_meta_value
+         */
+        public function test_set_subtype_meta_value( $post_type, $meta_key, $single, $in_post_type, $can_write ) {
+                $post_id  = self::$post_id;
+                $endpoint = 'posts';
+                if ( 'cpt' === $post_type ) {
+                        $post_id  = self::$cpt_post_id;
+                        $endpoint = 'cpt';
+                }
+
+                $meta_value = 'value_to_set';
+
+                $this->grant_write_permission();
+
+                $request = new WP_REST_Request( 'POST', sprintf( '/wp/v2/%s/%d', $endpoint, $post_id ) );
+                $request->set_body_params( array(
+                        'meta' => array(
+                                $meta_key => $meta_value,
+                        ),
+                ) );
+
+                $response = rest_get_server()->dispatch( $request );
+                if ( ! $can_write ) {
+                        $this->assertEquals( 403, $response->get_status() );
+                        $this->assertEmpty( get_post_meta( $post_id, $meta_key, $single ) );
+                        return;
+                }
+
+                $this->assertEquals( 200, $response->get_status() );
+
+                $data = $response->get_data();
+                $this->assertArrayHasKey( 'meta', $data );
+                $this->assertInternalType( 'array', $data['meta'] );
+
+                if ( $in_post_type ) {
+                        $expected_value = $meta_value;
+                        if ( ! $single ) {
+                                $expected_value = array( $expected_value );
+                        }
+
+                        $this->assertEquals( $expected_value, get_post_meta( $post_id, $meta_key, $single ) );
+                        $this->assertArrayHasKey( $meta_key, $data['meta'] );
+                        $this->assertEquals( $expected_value, $data['meta'][ $meta_key ] );
+                } else {
+                        $this->assertEmpty( get_post_meta( $post_id, $meta_key, $single ) );
+                        $this->assertArrayNotHasKey( $meta_key, $data['meta'] );
+                }
+        }
+
+        public function data_set_subtype_meta_value() {
+                $data = $this->data_get_subtype_meta_value();
+
+                foreach ( $data as $index => $dataset ) {
+                        $can_write = true;
+
+                        // This combination is not writable because of an auth callback of '__return_false'.
+                        if ( 'cpt' === $dataset[0] && 'test_single' === $dataset[1] ) {
+                                $can_write = false;
+                        }
+
+                        $data[ $index ][] = $can_write;
+                }
+
+                return $data;
+        }
+
         /**
          * Internal function used to disable an insert query which
          * will trigger a wpdb error for testing purposes.

tests/phpunit/tests/rest-api/rest-term-meta-fields.php

@@ -12 +12 @@
 class WP_Test_REST_Term_Meta_Fields extends WP_Test_REST_TestCase {
         protected static $wp_meta_keys_saved;
         protected static $category_id;
+        protected static $customtax_term_id;
 
         public static function wpSetUpBeforeClass( $factory ) {
+                register_taxonomy( 'customtax', 'post', array(
+                        'show_in_rest' => true,
+                ) );
+
                 self::$wp_meta_keys_saved = isset( $GLOBALS['wp_meta_keys'] ) ? $GLOBALS['wp_meta_keys'] : array();
                 self::$category_id        = $factory->category->create();
+                self::$customtax_term_id  = $factory->term->create( array( 'taxonomy' => 'customtax' ) );
         }
 
         public static function wpTearDownAfterClass() {
                 $GLOBALS['wp_meta_keys'] = self::$wp_meta_keys_saved;
                 wp_delete_term( self::$category_id, 'category' );
+                wp_delete_term( self::$customtax_term_id, 'customtax' );
+
+                unregister_taxonomy( 'customtax' );
         }
 
         public function setUp() {
@@ -120 +129 @@
                         )
                 );
 
+                register_taxonomy( 'customtax', 'post', array(
+                        'show_in_rest' => true,
+                ) );
+
+                register_term_meta( 'customtax', 'test_customtax_single', array(
+                        'show_in_rest'   => true,
+                        'single'         => true,
+                ) );
+
+                register_term_meta( 'customtax', 'test_customtax_multi', array(
+                        'show_in_rest'   => true,
+                        'single'         => false,
+                ) );
+
+                // Register 'test_single' on subtype to override for bad auth.
+                register_term_meta( 'customtax', 'test_single', array(
+                        'show_in_rest'   => true,
+                        'single'         => true,
+                        'auth_callback'  => '__return_false',
+                ) );
+
                 /** @var WP_REST_Server $wp_rest_server */
                 global $wp_rest_server;
                 $wp_rest_server = new Spy_REST_Server;
@@ -1047 +1077 @@
                 $this->assertArrayNotHasKey( 'test_no_type', $meta_schema );
         }
 
+        /**
+         * @ticket 38323
+         * @dataProvider data_get_subtype_meta_value
+         */
+        public function test_get_subtype_meta_value( $taxonomy, $meta_key, $single, $in_taxonomy ) {
+                $term_id  = self::$category_id;
+                $endpoint = 'categories';
+                if ( 'customtax' === $taxonomy ) {
+                        $term_id  = self::$customtax_term_id;
+                        $endpoint = 'customtax';
+                }
+
+                $meta_value = 'testvalue';
+
+                add_term_meta( $term_id, $meta_key, $meta_value );
+
+                $request = new WP_REST_Request( 'GET', sprintf( '/wp/v2/%s/%d', $endpoint, $term_id ) );
+                $response = rest_get_server()->dispatch( $request );
+
+                $this->assertEquals( 200, $response->get_status() );
+
+                $data = $response->get_data();
+
+                $this->assertArrayHasKey( 'meta', $data );
+                $this->assertInternalType( 'array', $data['meta'] );
+
+                if ( $in_taxonomy ) {
+                        $expected_value = $meta_value;
+                        if ( ! $single ) {
+                                $expected_value = array( $expected_value );
+                        }
+
+                        $this->assertArrayHasKey( $meta_key, $data['meta'] );
+                        $this->assertEquals( $expected_value, $data['meta'][ $meta_key ] );
+                } else {
+                        $this->assertArrayNotHasKey( $meta_key, $data['meta'] );
+                }
+        }
+
+        public function data_get_subtype_meta_value() {
+                return array(
+                        array( 'customtax', 'test_customtax_single', true, true ),
+                        array( 'customtax', 'test_customtax_multi', false, true ),
+                        array( 'customtax', 'test_single', true, true ),
+                        array( 'customtax', 'test_multi', false, true ),
+                        array( 'category', 'test_customtax_single', true, false ),
+                        array( 'category', 'test_customtax_multi', false, false ),
+                        array( 'category', 'test_single', true, true ),
+                        array( 'category', 'test_multi', false, true ),
+                );
+        }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_set_subtype_meta_value
+         */
+        public function test_set_subtype_meta_value( $taxonomy, $meta_key, $single, $in_taxonomy, $can_write ) {
+                $term_id  = self::$category_id;
+                $endpoint = 'categories';
+                if ( 'customtax' === $taxonomy ) {
+                        $term_id  = self::$customtax_term_id;
+                        $endpoint = 'customtax';
+                }
+
+                $meta_value = 'value_to_set';
+
+                $this->grant_write_permission();
+
+                $request = new WP_REST_Request( 'POST', sprintf( '/wp/v2/%s/%d', $endpoint, $term_id ) );
+                $request->set_body_params( array(
+                        'meta' => array(
+                                $meta_key => $meta_value,
+                        ),
+                ) );
+
+                $response = rest_get_server()->dispatch( $request );
+                if ( ! $can_write ) {
+                        $this->assertEquals( 403, $response->get_status() );
+                        $this->assertEmpty( get_term_meta( $term_id, $meta_key, $single ) );
+                        return;
+                }
+
+                $this->assertEquals( 200, $response->get_status() );
+
+                $data = $response->get_data();
+                $this->assertArrayHasKey( 'meta', $data );
+                $this->assertInternalType( 'array', $data['meta'] );
+
+                if ( $in_taxonomy ) {
+                        $expected_value = $meta_value;
+                        if ( ! $single ) {
+                                $expected_value = array( $expected_value );
+                        }
+
+                        $this->assertEquals( $expected_value, get_term_meta( $term_id, $meta_key, $single ) );
+                        $this->assertArrayHasKey( $meta_key, $data['meta'] );
+                        $this->assertEquals( $expected_value, $data['meta'][ $meta_key ] );
+                } else {
+                        $this->assertEmpty( get_term_meta( $term_id, $meta_key, $single ) );
+                        $this->assertArrayNotHasKey( $meta_key, $data['meta'] );
+                }
+        }
+
+        public function data_set_subtype_meta_value() {
+                $data = $this->data_get_subtype_meta_value();
+
+                foreach ( $data as $index => $dataset ) {
+                        $can_write = true;
+
+                        // This combination is not writable because of an auth callback of '__return_false'.
+                        if ( 'customtax' === $dataset[0] && 'test_single' === $dataset[1] ) {
+                                $can_write = false;
+                        }
+
+                        $data[ $index ][] = $can_write;
+                }
+
+                return $data;
+        }
+
         /**
          * Internal function used to disable an insert query which
          * will trigger a wpdb error for testing purposes.

tests/phpunit/tests/term/meta.php

@@ -6 +6 @@
  * @ticket 10142
  */
 class Tests_Term_Meta extends WP_UnitTestCase {
+
+        private $last_register_meta_call = array(
+                'object_type' => '',
+                'meta_key'    => '',
+                'args'        => array(),
+        );
+
         public function setUp() {
                 parent::setUp();
                 register_taxonomy( 'wptests_tax', 'post' );
@@ -463 +470 @@
         public static function set_cache_results( $q ) {
                 $q->set( 'cache_results', true );
         }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_register_term_meta
+         */
+        public function test_register_term_meta( $taxonomy, $meta_key, $args ) {
+                add_filter( 'register_meta_args', array( $this, 'filter_register_meta_args_set_last_register_meta_call' ), 10, 4 );
+
+                register_term_meta( $taxonomy, $meta_key, $args );
+
+                $args['object_subtype'] = $taxonomy;
+
+                // Reset global so subsequent data tests do not get polluted.
+                $GLOBALS['wp_meta_keys'] = array();
+
+                $this->assertEquals( 'term', $this->last_register_meta_call['object_type'] );
+                $this->assertEquals( $meta_key, $this->last_register_meta_call['meta_key'] );
+                $this->assertEquals( $args, $this->last_register_meta_call['args'] );
+        }
+
+        public function data_register_term_meta() {
+                return array(
+                        array( 'wptests_tax', 'registered_key1', array( 'single' => true ) ),
+                        array( 'category', 'registered_key2', array() ),
+                        array( '', 'registered_key3', array( 'sanitize_callback' => 'absint' ) ),
+                );
+        }
+
+        public function filter_register_meta_args_set_last_register_meta_call( $args, $defaults, $object_type, $meta_key ) {
+                $this->last_register_meta_call['object_type'] = $object_type;
+                $this->last_register_meta_call['meta_key']    = $meta_key;
+                $this->last_register_meta_call['args']        = $args;
+
+                return $args;
+        }
+
+        /**
+         * @ticket 38323
+         * @dataProvider data_unregister_term_meta
+         */
+        public function test_unregister_term_meta( $taxonomy, $meta_key ) {
+                global $wp_meta_keys;
+
+                register_term_meta( $taxonomy, $meta_key, array() );
+                unregister_term_meta( $taxonomy, $meta_key );
+
+                $actual = $wp_meta_keys;
+
+                // Reset global so subsequent data tests do not get polluted.
+                $wp_meta_keys = array();
+
+                $this->assertEmpty( $actual );
+        }
+
+        public function data_unregister_term_meta() {
+                return array(
+                        array( 'wptests_tax', 'registered_key1' ),
+                        array( 'category', 'registered_key2' ),
+                        array( '', 'registered_key3' ),
+                );
+        }
 }