wp/wp-includes/widgets.php
changeset 7 cf61fcea0001
parent 5 5e2f62d02dcd
child 9 177826044cd9
--- a/wp/wp-includes/widgets.php	Tue Jun 09 11:14:17 2015 +0000
+++ b/wp/wp-includes/widgets.php	Mon Oct 14 17:39:30 2019 +0200
@@ -1,9 +1,13 @@
 <?php
 /**
- * API for creating dynamic sidebar without hardcoding functionality into
- * themes. Includes both internal WordPress routines and theme use routines.
+ * Core Widgets API
  *
- * This functionality was found in a plugin before WordPress 2.2 release which
+ * This API is used for creating dynamic sidebar without hardcoding functionality into
+ * themes
+ *
+ * Includes both internal WordPress routines and theme-use routines.
+ *
+ * This functionality was found in a plugin before the WordPress 2.2 release, which
  * included it in the core from that point on.
  *
  * @link https://codex.wordpress.org/Plugins/WordPress_Widgets WordPress Widgets
@@ -11,593 +15,12 @@
  *
  * @package WordPress
  * @subpackage Widgets
+ * @since 2.2.0
  */
 
-/**
- * This class must be extended for each widget and WP_Widget::widget(), WP_Widget::update()
- * and WP_Widget::form() need to be over-ridden.
- *
- * @package WordPress
- * @subpackage Widgets
- * @since 2.8.0
- */
-class WP_Widget {
-
-	/**
-	 * Root ID for all widgets of this type.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 * @var mixed|string
-	 */
-	public $id_base;
-
-	/**
-	 * Name for this widget type.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 * @var string
-	 */
-	public $name;
-
-	/**
-	 * Option array passed to {@see wp_register_sidebar_widget()}.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 * @var array
-	 */
-	public $widget_options;
-
-	/**
-	 * Option array passed to {@see wp_register_widget_control()}.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 * @var array
-	 */
-	public $control_options;
-
-	/**
-	 * Unique ID number of the current instance.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 * @var bool|int
-	 */
-	public $number = false;
-
-	/**
-	 * Unique ID string of the current instance (id_base-number).
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 * @var bool|string
-	 */
-	public $id = false;
-
-	/**
-	 * Whether the widget data has been updated.
-	 *
-	 * Set to true when the data is updated after a POST submit - ensures it does
-	 * not happen twice.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 * @var bool
-	 */
-	public $updated = false;
-
-	// Member functions that you must over-ride.
-
-	/**
-	 * Echo the widget content.
-	 *
-	 * Subclasses should over-ride this function to generate their widget code.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @param array $args     Display arguments including before_title, after_title,
-	 *                        before_widget, and after_widget.
-	 * @param array $instance The settings for the particular instance of the widget.
-	 */
-	public function widget( $args, $instance ) {
-		die('function WP_Widget::widget() must be over-ridden in a sub-class.');
-	}
-
-	/**
-	 * Update a particular instance.
-	 *
-	 * This function should check that $new_instance is set correctly. The newly-calculated
-	 * value of `$instance` should be returned. If false is returned, the instance won't be
-	 * saved/updated.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @param array $new_instance New settings for this instance as input by the user via
-	 *                            {@see WP_Widget::form()}.
-	 * @param array $old_instance Old settings for this instance.
-	 * @return array Settings to save or bool false to cancel saving.
-	 */
-	public function update( $new_instance, $old_instance ) {
-		return $new_instance;
-	}
-
-	/**
-	 * Output the settings update form.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @param array $instance Current settings.
-	 * @return string Default return is 'noform'.
-	 */
-	public function form($instance) {
-		echo '<p class="no-options-widget">' . __('There are no options for this widget.') . '</p>';
-		return 'noform';
-	}
-
-	// Functions you'll need to call.
-
-	/**
-	 * PHP5 constructor.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @param string $id_base         Optional Base ID for the widget, lowercase and unique. If left empty,
-	 *                                a portion of the widget's class name will be used Has to be unique.
-	 * @param string $name            Name for the widget displayed on the configuration page.
-	 * @param array  $widget_options  Optional. Widget options. See {@see wp_register_sidebar_widget()} for
-	 *                                information on accepted arguments. Default empty array.
-	 * @param array  $control_options Optional. Widget control options. See {@see wp_register_widget_control()}
-	 *                                for information on accepted arguments. Default empty array.
-	 */
-	public function __construct( $id_base, $name, $widget_options = array(), $control_options = array() ) {
-		$this->id_base = empty($id_base) ? preg_replace( '/(wp_)?widget_/', '', strtolower(get_class($this)) ) : strtolower($id_base);
-		$this->name = $name;
-		$this->option_name = 'widget_' . $this->id_base;
-		$this->widget_options = wp_parse_args( $widget_options, array('classname' => $this->option_name) );
-		$this->control_options = wp_parse_args( $control_options, array('id_base' => $this->id_base) );
-	}
-
-	/**
-	 * PHP4 constructor
-	 *
-	 * @param string $id_base
-	 * @param string $name
-	 * @param array  $widget_options
-	 * @param array  $control_options
-	 */
-	public function WP_Widget( $id_base, $name, $widget_options = array(), $control_options = array() ) {
-		WP_Widget::__construct( $id_base, $name, $widget_options, $control_options );
-	}
-
-	/**
-	 * Constructs name attributes for use in form() fields
-	 *
-	 * This function should be used in form() methods to create name attributes for fields to be saved by update()
-	 *
-	 * @param string $field_name Field name
-	 * @return string Name attribute for $field_name
-	 */
-	public function get_field_name($field_name) {
-		return 'widget-' . $this->id_base . '[' . $this->number . '][' . $field_name . ']';
-	}
-
-	/**
-	 * Constructs id attributes for use in {@see WP_Widget::form()} fields.
-	 *
-	 * This function should be used in form() methods to create id attributes
-	 * for fields to be saved by {@see WP_Widget::update()}.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @param string $field_name Field name.
-	 * @return string ID attribute for `$field_name`.
-	 */
-	public function get_field_id( $field_name ) {
-		return 'widget-' . $this->id_base . '-' . $this->number . '-' . $field_name;
-	}
-
-	/**
-	 * Register all widget instances of this widget class.
-	 *
-	 * @since 2.8.0
-	 * @access private
-	 */
-	public function _register() {
-		$settings = $this->get_settings();
-		$empty = true;
-
-		if ( is_array($settings) ) {
-			foreach ( array_keys($settings) as $number ) {
-				if ( is_numeric($number) ) {
-					$this->_set($number);
-					$this->_register_one($number);
-					$empty = false;
-				}
-			}
-		}
-
-		if ( $empty ) {
-			// If there are none, we register the widget's existence with a
-			// generic template
-			$this->_set(1);
-			$this->_register_one();
-		}
-	}
-
-	/**
-	 * Set the internal order number for the widget instance.
-	 *
-	 * @since 2.8.0
-	 * @access private
-	 *
-	 * @param int $number The unique order number of this widget instance compared to other
-	 *                    instances of the same class.
-	 */
-	public function _set($number) {
-		$this->number = $number;
-		$this->id = $this->id_base . '-' . $number;
-	}
-
-	public function _get_display_callback() {
-		return array($this, 'display_callback');
-	}
-
-	public function _get_update_callback() {
-		return array($this, 'update_callback');
-	}
-
-	public function _get_form_callback() {
-		return array($this, 'form_callback');
-	}
-
-	/**
-	 * Determine whether the current request is inside the Customizer preview.
-	 *
-	 * If true -- the current request is inside the Customizer preview, then
-	 * the object cache gets suspended and widgets should check this to decide
-	 * whether they should store anything persistently to the object cache,
-	 * to transients, or anywhere else.
-	 *
-	 * @since 3.9.0
-	 * @access public
-	 *
-	 * @return bool True if within the Customizer preview, false if not.
-	 */
-	public function is_preview() {
-		global $wp_customize;
-		return ( isset( $wp_customize ) && $wp_customize->is_preview() ) ;
-	}
-
-	/**
-	 * Generate the actual widget content (Do NOT override).
-	 *
-	 * Finds the instance and calls {@see WP_Widget::widget()}.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @param array     $args        Display arguments. See {@see WP_Widget::widget()} for information
-	 *                               on accepted arguments.
-	 * @param int|array $widget_args {
-	 *     Optional. Internal order number of the widget instance, or array of multi-widget arguments.
-	 *     Default 1.
-	 *
-	 *     @type int $number Number increment used for multiples of the same widget.
-	 * }
-	 */
-	public function display_callback( $args, $widget_args = 1 ) {
-		if ( is_numeric($widget_args) )
-			$widget_args = array( 'number' => $widget_args );
-
-		$widget_args = wp_parse_args( $widget_args, array( 'number' => -1 ) );
-		$this->_set( $widget_args['number'] );
-		$instance = $this->get_settings();
-
-		if ( array_key_exists( $this->number, $instance ) ) {
-			$instance = $instance[$this->number];
-
-			/**
-			 * Filter the settings for a particular widget instance.
-			 *
-			 * Returning false will effectively short-circuit display of the widget.
-			 *
-			 * @since 2.8.0
-			 *
-			 * @param array     $instance The current widget instance's settings.
-			 * @param WP_Widget $this     The current widget instance.
-			 * @param array     $args     An array of default widget arguments.
-			 */
-			$instance = apply_filters( 'widget_display_callback', $instance, $this, $args );
-
-			if ( false === $instance ) {
-				return;
-			}
-
-			$was_cache_addition_suspended = wp_suspend_cache_addition();
-			if ( $this->is_preview() && ! $was_cache_addition_suspended ) {
-				wp_suspend_cache_addition( true );
-			}
-
-			$this->widget( $args, $instance );
-
-			if ( $this->is_preview() ) {
-				wp_suspend_cache_addition( $was_cache_addition_suspended );
-			}
-		}
-	}
-
-	/**
-	 * Deal with changed settings (Do NOT override).
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @param int $deprecated Not used.
-	 */
-	public function update_callback( $deprecated = 1 ) {
-		global $wp_registered_widgets;
-
-		$all_instances = $this->get_settings();
-
-		// We need to update the data
-		if ( $this->updated )
-			return;
-
-		if ( isset($_POST['delete_widget']) && $_POST['delete_widget'] ) {
-			// Delete the settings for this instance of the widget
-			if ( isset($_POST['the-widget-id']) )
-				$del_id = $_POST['the-widget-id'];
-			else
-				return;
-
-			if ( isset($wp_registered_widgets[$del_id]['params'][0]['number']) ) {
-				$number = $wp_registered_widgets[$del_id]['params'][0]['number'];
-
-				if ( $this->id_base . '-' . $number == $del_id )
-					unset($all_instances[$number]);
-			}
-		} else {
-			if ( isset($_POST['widget-' . $this->id_base]) && is_array($_POST['widget-' . $this->id_base]) ) {
-				$settings = $_POST['widget-' . $this->id_base];
-			} elseif ( isset($_POST['id_base']) && $_POST['id_base'] == $this->id_base ) {
-				$num = $_POST['multi_number'] ? (int) $_POST['multi_number'] : (int) $_POST['widget_number'];
-				$settings = array( $num => array() );
-			} else {
-				return;
-			}
-
-			foreach ( $settings as $number => $new_instance ) {
-				$new_instance = stripslashes_deep($new_instance);
-				$this->_set($number);
-
-				$old_instance = isset($all_instances[$number]) ? $all_instances[$number] : array();
-
-				$was_cache_addition_suspended = wp_suspend_cache_addition();
-				if ( $this->is_preview() && ! $was_cache_addition_suspended ) {
-					wp_suspend_cache_addition( true );
-				}
-
-				$instance = $this->update( $new_instance, $old_instance );
-
-				if ( $this->is_preview() ) {
-					wp_suspend_cache_addition( $was_cache_addition_suspended );
-				}
-
-				/**
-				 * Filter a widget's settings before saving.
-				 *
-				 * Returning false will effectively short-circuit the widget's ability
-				 * to update settings.
-				 *
-				 * @since 2.8.0
-				 *
-				 * @param array     $instance     The current widget instance's settings.
-				 * @param array     $new_instance Array of new widget settings.
-				 * @param array     $old_instance Array of old widget settings.
-				 * @param WP_Widget $this         The current widget instance.
-				 */
-				$instance = apply_filters( 'widget_update_callback', $instance, $new_instance, $old_instance, $this );
-				if ( false !== $instance ) {
-					$all_instances[$number] = $instance;
-				}
-
-				break; // run only once
-			}
-		}
-
-		$this->save_settings($all_instances);
-		$this->updated = true;
-	}
-
-	/**
-	 * Generate the widget control form (Do NOT override).
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @param int|array $widget_args Widget instance number or array of widget arguments.
-	 */
-	public function form_callback( $widget_args = 1 ) {
-		if ( is_numeric($widget_args) )
-			$widget_args = array( 'number' => $widget_args );
-
-		$widget_args = wp_parse_args( $widget_args, array( 'number' => -1 ) );
-		$all_instances = $this->get_settings();
-
-		if ( -1 == $widget_args['number'] ) {
-			// We echo out a form where 'number' can be set later
-			$this->_set('__i__');
-			$instance = array();
-		} else {
-			$this->_set($widget_args['number']);
-			$instance = $all_instances[ $widget_args['number'] ];
-		}
-
-		/**
-		 * Filter the widget instance's settings before displaying the control form.
-		 *
-		 * Returning false effectively short-circuits display of the control form.
-		 *
-		 * @since 2.8.0
-		 *
-		 * @param array     $instance The current widget instance's settings.
-		 * @param WP_Widget $this     The current widget instance.
-		 */
-		$instance = apply_filters( 'widget_form_callback', $instance, $this );
-
-		$return = null;
-		if ( false !== $instance ) {
-			$return = $this->form($instance);
-
-			/**
-			 * Fires at the end of the widget control form.
-			 *
-			 * Use this hook to add extra fields to the widget form. The hook
-			 * is only fired if the value passed to the 'widget_form_callback'
-			 * hook is not false.
-			 *
-			 * Note: If the widget has no form, the text echoed from the default
-			 * form method can be hidden using CSS.
-			 *
-			 * @since 2.8.0
-			 *
-			 * @param WP_Widget $this     The widget instance, passed by reference.
-			 * @param null      $return   Return null if new fields are added.
-			 * @param array     $instance An array of the widget's settings.
-			 */
-			do_action_ref_array( 'in_widget_form', array( &$this, &$return, $instance ) );
-		}
-		return $return;
-	}
-
-	/**
-	 * Register an instance of the widget class.
-	 *
-	 * @since 2.8.0
-	 * @access private
-	 *
-	 * @param integer $number Optional. The unique order number of this widget instance
-	 *                        compared to other instances of the same class. Default -1.
-	 */
-	public function _register_one( $number = -1 ) {
-		wp_register_sidebar_widget(	$this->id, $this->name,	$this->_get_display_callback(), $this->widget_options, array( 'number' => $number ) );
-		_register_widget_update_callback( $this->id_base, $this->_get_update_callback(), $this->control_options, array( 'number' => -1 ) );
-		_register_widget_form_callback(	$this->id, $this->name,	$this->_get_form_callback(), $this->control_options, array( 'number' => $number ) );
-	}
-
-	/**
-	 * Save the settings for all instances of the widget class.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @param array $settings Multi-dimensional array of widget instance settings.
-	 */
-	public function save_settings( $settings ) {
-		$settings['_multiwidget'] = 1;
-		update_option( $this->option_name, $settings );
-	}
-
-	/**
-	 * Get the settings for all instances of the widget class.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @return array Multi-dimensional array of widget instance settings.
-	 */
-	public function get_settings() {
-
-		$settings = get_option($this->option_name);
-
-		if ( false === $settings && isset($this->alt_option_name) )
-			$settings = get_option($this->alt_option_name);
-
-		if ( !is_array($settings) )
-			$settings = array();
-
-		if ( !empty($settings) && !array_key_exists('_multiwidget', $settings) ) {
-			// old format, convert if single widget
-			$settings = wp_convert_widget_settings($this->id_base, $this->option_name, $settings);
-		}
-
-		unset($settings['_multiwidget'], $settings['__i__']);
-		return $settings;
-	}
-}
-
-/**
- * Singleton that registers and instantiates WP_Widget classes.
- *
- * @package WordPress
- * @subpackage Widgets
- * @since 2.8.0
- */
-class WP_Widget_Factory {
-	public $widgets = array();
-
-	public function WP_Widget_Factory() {
-		add_action( 'widgets_init', array( $this, '_register_widgets' ), 100 );
-	}
-
-	/**
-	 * Register a widget subclass.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @param string $widget_class The name of a {@see WP_Widget} subclass.
-	 */
-	public function register( $widget_class ) {
-		$this->widgets[$widget_class] = new $widget_class();
-	}
-
-	/**
-	 * Un-register a widget subclass.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 *
-	 * @param string $widget_class The name of a {@see WP_Widget} subclass.
-	 */
-	public function unregister( $widget_class ) {
-		if ( isset($this->widgets[$widget_class]) )
-			unset($this->widgets[$widget_class]);
-	}
-
-	/**
-	 * Utility method for adding widgets to the registered widgets global.
-	 *
-	 * @since 2.8.0
-	 * @access public
-	 */
-	public function _register_widgets() {
-		global $wp_registered_widgets;
-		$keys = array_keys($this->widgets);
-		$registered = array_keys($wp_registered_widgets);
-		$registered = array_map('_get_widget_id_base', $registered);
-
-		foreach ( $keys as $key ) {
-			// don't register new widget if old widget with the same id is already registered
-			if ( in_array($this->widgets[$key]->id_base, $registered, true) ) {
-				unset($this->widgets[$key]);
-				continue;
-			}
-
-			$this->widgets[$key]->_register();
-		}
-	}
-}
-
-/* Global Variables */
+//
+// Global Variables
+//
 
 /** @ignore */
 global $wp_registered_sidebars, $wp_registered_widgets, $wp_registered_widget_controls, $wp_registered_widget_updates;
@@ -625,15 +48,22 @@
  * @since 2.2.0
  */
 $wp_registered_widget_controls = array();
+/**
+ * @global array $wp_registered_widget_updates
+ */
 $wp_registered_widget_updates = array();
 
 /**
  * Private
+ *
+ * @global array $_wp_sidebars_widgets
  */
 $_wp_sidebars_widgets = array();
 
 /**
  * Private
+ *
+ * @global array $_wp_deprecated_widgets_callbacks
  */
 $GLOBALS['_wp_deprecated_widgets_callbacks'] = array(
 	'wp_widget_pages',
@@ -660,7 +90,9 @@
 	'wp_widget_recent_comments_control'
 );
 
-/* Template tags & API functions */
+//
+// Template tags & API functions
+//
 
 /**
  * Register a widget
@@ -668,37 +100,41 @@
  * Registers a WP_Widget widget
  *
  * @since 2.8.0
+ * @since 4.6.0 Updated the `$widget` parameter to also accept a WP_Widget instance object
+ *              instead of simply a `WP_Widget` subclass name.
  *
  * @see WP_Widget
- * @see WP_Widget_Factory
- * @uses WP_Widget_Factory
+ *
+ * @global WP_Widget_Factory $wp_widget_factory
  *
- * @param string $widget_class The name of a class that extends WP_Widget
+ * @param string|WP_Widget $widget Either the name of a `WP_Widget` subclass or an instance of a `WP_Widget` subclass.
  */
-function register_widget($widget_class) {
+function register_widget( $widget ) {
 	global $wp_widget_factory;
 
-	$wp_widget_factory->register($widget_class);
+	$wp_widget_factory->register( $widget );
 }
 
 /**
- * Unregister a widget
+ * Unregisters a widget.
  *
- * Unregisters a WP_Widget widget. Useful for unregistering default widgets.
- * Run within a function hooked to the widgets_init action.
+ * Unregisters a WP_Widget widget. Useful for un-registering default widgets.
+ * Run within a function hooked to the {@see 'widgets_init'} action.
  *
  * @since 2.8.0
+ * @since 4.6.0 Updated the `$widget` parameter to also accept a WP_Widget instance object
+ *              instead of simply a `WP_Widget` subclass name.
  *
  * @see WP_Widget
- * @see WP_Widget_Factory
- * @uses WP_Widget_Factory
+ *
+ * @global WP_Widget_Factory $wp_widget_factory
  *
- * @param string $widget_class The name of a class that extends WP_Widget
+ * @param string|WP_Widget $widget Either the name of a `WP_Widget` subclass or an instance of a `WP_Widget` subclass.
  */
-function unregister_widget($widget_class) {
+function unregister_widget( $widget ) {
 	global $wp_widget_factory;
 
-	$wp_widget_factory->unregister($widget_class);
+	$wp_widget_factory->unregister( $widget );
 }
 
 /**
@@ -712,6 +148,8 @@
  *
  * @see register_sidebar() The second parameter is documented by register_sidebar() and is the same here.
  *
+ * @global array $wp_registered_sidebars
+ *
  * @param int          $number Optional. Number of sidebars to create. Default 1.
  * @param array|string $args {
  *     Optional. Array or string of arguments for building a sidebar.
@@ -745,13 +183,14 @@
 		if ( isset($args['id']) ) {
 			$_args['id'] = $args['id'];
 			$n = 2; // Start at -2 for conflicting custom ID's
-			while ( isset($wp_registered_sidebars[$_args['id']]) )
+			while ( is_registered_sidebar( $_args['id'] ) ) {
 				$_args['id'] = $args['id'] . '-' . $n++;
+			}
 		} else {
-			$n = count($wp_registered_sidebars);
+			$n = count( $wp_registered_sidebars );
 			do {
 				$_args['id'] = 'sidebar-' . ++$n;
-			} while ( isset($wp_registered_sidebars[$_args['id']]) );
+			} while ( is_registered_sidebar( $_args['id'] ) );
 		}
 		register_sidebar($_args);
 	}
@@ -844,15 +283,30 @@
  *
  * @since 2.2.0
  *
- * @uses $wp_registered_sidebars Stores the new sidebar in this array by sidebar ID.
+ * @global array $wp_registered_sidebars Stores the new sidebar in this array by sidebar ID.
  *
- * @param string $name The ID of the sidebar when it was added.
+ * @param string|int $sidebar_id The ID of the sidebar when it was registered.
  */
-function unregister_sidebar( $name ) {
+function unregister_sidebar( $sidebar_id ) {
 	global $wp_registered_sidebars;
 
-	if ( isset( $wp_registered_sidebars[$name] ) )
-		unset( $wp_registered_sidebars[$name] );
+	unset( $wp_registered_sidebars[ $sidebar_id ] );
+}
+
+/**
+ * Checks if a sidebar is registered.
+ *
+ * @since 4.4.0
+ *
+ * @global array $wp_registered_sidebars Registered sidebars.
+ *
+ * @param string|int $sidebar_id The ID of the sidebar when it was registered.
+ * @return bool True if the sidebar is registered, false otherwise.
+ */
+function is_registered_sidebar( $sidebar_id ) {
+	global $wp_registered_sidebars;
+
+	return isset( $wp_registered_sidebars[ $sidebar_id ] );
 }
 
 /**
@@ -865,12 +319,14 @@
  *
  * @since 2.2.0
  *
- * @global array $wp_registered_widgets       Uses stored registered widgets.
- * @global array $wp_register_widget_defaults Retrieves widget defaults.
+ * @global array $wp_registered_widgets            Uses stored registered widgets.
+ * @global array $wp_registered_widget_controls    Stores the registered widget controls (options).
+ * @global array $wp_registered_widget_updates
+ * @global array $_wp_deprecated_widgets_callbacks
  *
  * @param int|string $id              Widget ID.
  * @param string     $name            Widget display title.
- * @param callback   $output_callback Run when widget is called.
+ * @param callable   $output_callback Run when widget is called.
  * @param array      $options {
  *     Optional. An array of supplementary widget options for the instance.
  *
@@ -879,7 +335,6 @@
  *     @type string $description Widget description for display in the widget administration
  *                               panel and/or theme.
  * }
- * @return null Will return if `$output_callback` is empty after removing widget.
  */
 function wp_register_sidebar_widget( $id, $name, $output_callback, $options = array() ) {
 	global $wp_registered_widgets, $wp_registered_widget_controls, $wp_registered_widget_updates, $_wp_deprecated_widgets_callbacks;
@@ -893,12 +348,8 @@
 
 	$id_base = _get_widget_id_base($id);
 	if ( in_array($output_callback, $_wp_deprecated_widgets_callbacks, true) && !is_callable($output_callback) ) {
-		if ( isset($wp_registered_widget_controls[$id]) )
-			unset($wp_registered_widget_controls[$id]);
-
-		if ( isset($wp_registered_widget_updates[$id_base]) )
-			unset($wp_registered_widget_updates[$id_base]);
-
+		unset( $wp_registered_widget_controls[ $id ] );
+		unset( $wp_registered_widget_updates[ $id_base ] );
 		return;
 	}
 
@@ -935,8 +386,10 @@
  *
  * @since 2.5.0
  *
+ * @global array $wp_registered_widgets
+ *
  * @param int|string $id Widget ID.
- * @return string Widget description, if available. Null on failure to retrieve description.
+ * @return string|void Widget description, if available.
  */
 function wp_widget_description( $id ) {
 	if ( !is_scalar($id) )
@@ -956,8 +409,10 @@
  *
  * @since 2.9.0
  *
+ * @global array $wp_registered_sidebars
+ *
  * @param string $id sidebar ID.
- * @return string Sidebar description, if available. Null on failure to retrieve description.
+ * @return string|void Sidebar description, if available.
  */
 function wp_sidebar_description( $id ) {
 	if ( !is_scalar($id) )
@@ -965,8 +420,9 @@
 
 	global $wp_registered_sidebars;
 
-	if ( isset($wp_registered_sidebars[$id]['description']) )
-		return esc_html( $wp_registered_sidebars[$id]['description'] );
+	if ( isset( $wp_registered_sidebars[ $id ]['description'] ) ) {
+		return wp_kses( $wp_registered_sidebars[ $id ]['description'], 'sidebar_description' );
+	}
 }
 
 /**
@@ -994,22 +450,27 @@
 /**
  * Registers widget control callback for customizing options.
  *
- * The options contains the 'height', 'width', and 'id_base' keys. The 'height'
- * option is never used. The 'width' option is the width of the fully expanded
- * control form, but try hard to use the default width. The 'id_base' is for
- * multi-widgets (widgets which allow multiple instances such as the text
- * widget), an id_base must be provided. The widget id will end up looking like
- * `{$id_base}-{$unique_number}`.
- *
  * @since 2.2.0
  *
- * @todo Document `$options` as a hash notation, re: WP_Widget::__construct() cross-reference.
  * @todo `$params` parameter?
  *
+ * @global array $wp_registered_widget_controls
+ * @global array $wp_registered_widget_updates
+ * @global array $wp_registered_widgets
+ * @global array $_wp_deprecated_widgets_callbacks
+ *
  * @param int|string   $id               Sidebar ID.
  * @param string       $name             Sidebar display name.
- * @param callback     $control_callback Run when sidebar is displayed.
- * @param array|string $options          Optional. Widget options. See description above. Default empty array.
+ * @param callable     $control_callback Run when sidebar is displayed.
+ * @param array $options {
+ *     Optional. Array or string of control options. Default empty array.
+ *
+ *     @type int        $height  Never used. Default 200.
+ *     @type int        $width   Width of the fully expanded control form (but try hard to use the default width).
+ *                               Default 250.
+ *     @type int|string $id_base Required for multi-widgets, i.e widgets that allow multiple instances such as the
+ *                               text widget. The widget id will end up looking like `{$id_base}-{$unique_number}`.
+ * }
  */
 function wp_register_widget_control( $id, $name, $control_callback, $options = array() ) {
 	global $wp_registered_widget_controls, $wp_registered_widget_updates, $wp_registered_widgets, $_wp_deprecated_widgets_callbacks;
@@ -1024,9 +485,7 @@
 	}
 
 	if ( in_array($control_callback, $_wp_deprecated_widgets_callbacks, true) && !is_callable($control_callback) ) {
-		if ( isset($wp_registered_widgets[$id]) )
-			unset($wp_registered_widgets[$id]);
-
+		unset( $wp_registered_widgets[ $id ] );
 		return;
 	}
 
@@ -1059,13 +518,18 @@
 }
 
 /**
+ * Registers the update callback for a widget.
+ *
+ * @since 2.8.0
  *
  * @global array $wp_registered_widget_updates
- * @param string   $id_base
- * @param callable $update_callback
- * @param array    $options
+ *
+ * @param string   $id_base         The base ID of a widget created by extending WP_Widget.
+ * @param callable $update_callback Update callback method for the widget.
+ * @param array    $options         Optional. Widget control options. See wp_register_widget_control().
+ *                                  Default empty array.
  */
-function _register_widget_update_callback($id_base, $update_callback, $options = array()) {
+function _register_widget_update_callback( $id_base, $update_callback, $options = array() ) {
 	global $wp_registered_widget_updates;
 
 	if ( isset($wp_registered_widget_updates[$id_base]) ) {
@@ -1084,13 +548,17 @@
 }
 
 /**
+ * Registers the form callback for a widget.
+ *
+ * @since 2.8.0
  *
  * @global array $wp_registered_widget_controls
- * @param int|string $id
- * @param string     $name
- * @param callable   $form_callback
- * @param array      $options
- * @return null
+ *
+ * @param int|string $id            Widget ID.
+ * @param string     $name          Name attribute for the widget.
+ * @param callable   $form_callback Form callback.
+ * @param array      $options       Optional. Widget control options. See wp_register_widget_control().
+ *                                  Default empty array.
  */
 function _register_widget_form_callback($id, $name, $form_callback, $options = array()) {
 	global $wp_registered_widget_controls;
@@ -1129,7 +597,7 @@
  * @param int|string $id Widget ID.
  */
 function wp_unregister_widget_control($id) {
-	return wp_register_widget_control($id, '', '');
+	wp_register_widget_control( $id, '', '' );
 }
 
 /**
@@ -1141,18 +609,21 @@
  *
  * @since 2.2.0
  *
+ * @global array $wp_registered_sidebars
+ * @global array $wp_registered_widgets
+ *
  * @param int|string $index Optional, default is 1. Index, name or ID of dynamic sidebar.
  * @return bool True, if widget sidebar was found and called. False if not found or not called.
  */
-function dynamic_sidebar($index = 1) {
+function dynamic_sidebar( $index = 1 ) {
 	global $wp_registered_sidebars, $wp_registered_widgets;
 
-	if ( is_int($index) ) {
+	if ( is_int( $index ) ) {
 		$index = "sidebar-$index";
 	} else {
-		$index = sanitize_title($index);
+		$index = sanitize_title( $index );
 		foreach ( (array) $wp_registered_sidebars as $key => $value ) {
-			if ( sanitize_title($value['name']) == $index ) {
+			if ( sanitize_title( $value['name'] ) == $index ) {
 				$index = $key;
 				break;
 			}
@@ -1161,19 +632,19 @@
 
 	$sidebars_widgets = wp_get_sidebars_widgets();
 	if ( empty( $wp_registered_sidebars[ $index ] ) || empty( $sidebars_widgets[ $index ] ) || ! is_array( $sidebars_widgets[ $index ] ) ) {
-		/** This action is documented in wp-includes/widgets.php */
+		/** This action is documented in wp-includes/widget.php */
 		do_action( 'dynamic_sidebar_before', $index, false );
-		/** This action is documented in wp-includes/widgets.php */
+		/** This action is documented in wp-includes/widget.php */
 		do_action( 'dynamic_sidebar_after',  $index, false );
-		/** This filter is documented in wp-includes/widgets.php */
+		/** This filter is documented in wp-includes/widget.php */
 		return apply_filters( 'dynamic_sidebar_has_widgets', false, $index );
 	}
 
 	/**
 	 * Fires before widgets are rendered in a dynamic sidebar.
 	 *
-	 * Note: The action also fires for empty sidebars, and on both the front-end
-	 * and back-end, including the Inactive Widgets sidebar on the Widgets screen.
+	 * Note: The action also fires for empty sidebars, and on both the front end
+	 * and back end, including the Inactive Widgets sidebar on the Widgets screen.
 	 *
 	 * @since 3.9.0
 	 *
@@ -1206,9 +677,9 @@
 		$params[0]['before_widget'] = sprintf($params[0]['before_widget'], $id, $classname_);
 
 		/**
-		 * Filter the parameters passed to a widget's display callback.
+		 * Filters the parameters passed to a widget's display callback.
 		 *
-		 * Note: The filter is evaluated on both the front-end and back-end,
+		 * Note: The filter is evaluated on both the front end and back end,
 		 * including for the Inactive Widgets sidebar on the Widgets screen.
 		 *
 		 * @since 2.5.0
@@ -1244,7 +715,7 @@
 		/**
 		 * Fires before a widget's display callback is called.
 		 *
-		 * Note: The action fires on both the front-end and back-end, including
+		 * Note: The action fires on both the front end and back end, including
 		 * for widgets in the Inactive Widgets sidebar on the Widgets screen.
 		 *
 		 * The action is not fired for empty sidebars.
@@ -1256,13 +727,13 @@
 		 *
 		 *     @type string $name                Name of the widget.
 		 *     @type string $id                  Widget ID.
-		 *     @type array|callback $callback    When the hook is fired on the front-end, $callback is an array
-		 *                                       containing the widget object. Fired on the back-end, $callback
+		 *     @type array|callable $callback    When the hook is fired on the front end, $callback is an array
+		 *                                       containing the widget object. Fired on the back end, $callback
 		 *                                       is 'wp_widget_control', see $_callback.
 		 *     @type array          $params      An associative array of multi-widget arguments.
 		 *     @type string         $classname   CSS class applied to the widget container.
 		 *     @type string         $description The widget description.
-		 *     @type array          $_callback   When the hook is fired on the back-end, $_callback is populated
+		 *     @type array          $_callback   When the hook is fired on the back end, $_callback is populated
 		 *                                       with an array containing the widget object, see $callback.
 		 * }
 		 */
@@ -1277,8 +748,8 @@
 	/**
 	 * Fires after widgets are rendered in a dynamic sidebar.
 	 *
-	 * Note: The action also fires for empty sidebars, and on both the front-end
-	 * and back-end, including the Inactive Widgets sidebar on the Widgets screen.
+	 * Note: The action also fires for empty sidebars, and on both the front end
+	 * and back end, including the Inactive Widgets sidebar on the Widgets screen.
 	 *
 	 * @since 3.9.0
 	 *
@@ -1289,10 +760,10 @@
 	do_action( 'dynamic_sidebar_after', $index, true );
 
 	/**
-	 * Filter whether a sidebar has widgets.
+	 * Filters whether a sidebar has widgets.
 	 *
-	 * Note: The filter is also evaluated for empty sidebars, and on both the front-end
-	 * and back-end, including the Inactive Widgets sidebar on the Widgets screen.
+	 * Note: The filter is also evaluated for empty sidebars, and on both the front end
+	 * and back end, including the Inactive Widgets sidebar on the Widgets screen.
 	 *
 	 * @since 3.9.0
 	 *
@@ -1300,14 +771,11 @@
 	 *                            Default false.
 	 * @param int|string $index   Index, name, or ID of the dynamic sidebar.
 	 */
-
-	$did_one = apply_filters( 'dynamic_sidebar_has_widgets', $did_one, $index );
-
-	return $did_one;
+	return apply_filters( 'dynamic_sidebar_has_widgets', $did_one, $index );
 }
 
 /**
- * Whether widget is displayed on the front-end.
+ * Whether widget is displayed on the front end.
  *
  * Either $callback or $id_base can be used
  * $id_base is the first argument when extending WP_Widget class
@@ -1317,17 +785,19 @@
  * the widget with that callback/$id_base AND that ID is found.
  *
  * NOTE: $widget_id and $id_base are the same for single widgets. To be effective
- * this function has to run after widgets have initialized, at action 'init' or later.
+ * this function has to run after widgets have initialized, at action {@see 'init'} or later.
  *
  * @since 2.2.0
  *
- * @param string $callback Optional, Widget callback to check.
- * @param int $widget_id Optional, but needed for checking. Widget ID.
- * @param string $id_base Optional, the base ID of a widget created by extending WP_Widget.
- * @param bool $skip_inactive Optional, whether to check in 'wp_inactive_widgets'.
- * @return mixed false if widget is not active or id of sidebar in which the widget is active.
+ * @global array $wp_registered_widgets
+ *
+ * @param string|false $callback      Optional, Widget callback to check. Default false.
+ * @param int|false    $widget_id     Optional. Widget ID. Optional, but needed for checking. Default false.
+ * @param string|false $id_base       Optional. The base ID of a widget created by extending WP_Widget. Default false.
+ * @param bool         $skip_inactive Optional. Whether to check in 'wp_inactive_widgets'. Default true.
+ * @return string|false False if widget is not active or id of sidebar in which the widget is active.
  */
-function is_active_widget($callback = false, $widget_id = false, $id_base = false, $skip_inactive = true) {
+function is_active_widget( $callback = false, $widget_id = false, $id_base = false, $skip_inactive = true ) {
 	global $wp_registered_widgets;
 
 	$sidebars_widgets = wp_get_sidebars_widgets();
@@ -1356,13 +826,16 @@
  *
  * @since 2.2.0
  *
+ * @global array $wp_registered_widgets
+ * @global array $wp_registered_sidebars
+ *
  * @return bool True, if using widgets. False, if not using widgets.
  */
 function is_dynamic_sidebar() {
 	global $wp_registered_widgets, $wp_registered_sidebars;
 	$sidebars_widgets = get_option('sidebars_widgets');
 	foreach ( (array) $wp_registered_sidebars as $index => $sidebar ) {
-		if ( count($sidebars_widgets[$index]) ) {
+		if ( ! empty( $sidebars_widgets[ $index ] ) ) {
 			foreach ( (array) $sidebars_widgets[$index] as $widget )
 				if ( array_key_exists($widget, $wp_registered_widgets) )
 					return true;
@@ -1385,7 +858,7 @@
 	$is_active_sidebar = ! empty( $sidebars_widgets[$index] );
 
 	/**
-	 * Filter whether a dynamic sidebar is considered "active".
+	 * Filters whether a dynamic sidebar is considered "active".
 	 *
 	 * @since 3.9.0
 	 *
@@ -1396,7 +869,9 @@
 	return apply_filters( 'is_active_sidebar', $is_active_sidebar, $index );
 }
 
-/* Internal Functions */
+//
+// Internal Functions
+//
 
 /**
  * Retrieve full list of sidebars and their widget instance IDs.
@@ -1407,6 +882,9 @@
  * @since 2.2.0
  * @access private
  *
+ * @global array $_wp_sidebars_widgets
+ * @global array $sidebars_widgets
+ *
  * @param bool $deprecated Not used (argument deprecated).
  * @return array Upgraded list of widgets to version 3 array format when called from the admin.
  */
@@ -1431,14 +909,13 @@
 		unset($sidebars_widgets['array_version']);
 
 	/**
-	 * Filter the list of sidebars and their widgets.
+	 * Filters the list of sidebars and their widgets.
 	 *
 	 * @since 2.7.0
 	 *
 	 * @param array $sidebars_widgets An associative array of sidebars and their widgets.
 	 */
-	$sidebars_widgets = apply_filters( 'sidebars_widgets', $sidebars_widgets );
-	return $sidebars_widgets;
+	return apply_filters( 'sidebars_widgets', $sidebars_widgets );
 }
 
 /**
@@ -1447,11 +924,19 @@
  * @since 2.2.0
  * @access private
  *
+ * @global array $_wp_sidebars_widgets
  * @param array $sidebars_widgets Sidebar widgets and their settings.
  */
 function wp_set_sidebars_widgets( $sidebars_widgets ) {
-	if ( !isset( $sidebars_widgets['array_version'] ) )
+	global $_wp_sidebars_widgets;
+
+	// Clear cached value used in wp_get_sidebars_widgets().
+	$_wp_sidebars_widgets = null;
+
+	if ( ! isset( $sidebars_widgets['array_version'] ) ) {
 		$sidebars_widgets['array_version'] = 3;
+	}
+
 	update_option( 'sidebars_widgets', $sidebars_widgets );
 }
 
@@ -1461,6 +946,8 @@
  * @since 2.2.0
  * @access private
  *
+ * @global array $wp_registered_sidebars
+ *
  * @return array
  */
 function wp_get_widget_defaults() {
@@ -1479,6 +966,8 @@
  *
  * @since 2.8.0
  *
+ * @global array $_wp_sidebars_widgets
+ *
  * @param string $base_name
  * @param string $option_name
  * @param array  $settings
@@ -1540,7 +1029,9 @@
  *
  * @since 2.8.0
  *
- * @param string $widget   The widget's PHP class name (see default-widgets.php).
+ * @global WP_Widget_Factory $wp_widget_factory
+ *
+ * @param string $widget   The widget's PHP class name (see class-wp-widget.php).
  * @param array  $instance Optional. The widget's instance settings. Default empty array.
  * @param array  $args {
  *     Optional. Array of arguments to configure the display of the widget.
@@ -1558,15 +1049,26 @@
 function the_widget( $widget, $instance = array(), $args = array() ) {
 	global $wp_widget_factory;
 
+	if ( ! isset( $wp_widget_factory->widgets[ $widget ] ) ) {
+		/* translators: %s: register_widget() */
+		_doing_it_wrong( __FUNCTION__, sprintf( __( 'Widgets need to be registered using %s, before they can be displayed.' ), '<code>register_widget()</code>' ), '4.9.0' );
+		return;
+	}
+
 	$widget_obj = $wp_widget_factory->widgets[$widget];
 	if ( ! ( $widget_obj instanceof WP_Widget ) ) {
 		return;
 	}
 
-	$before_widget = sprintf('<div class="widget %s">', $widget_obj->widget_options['classname'] );
-	$default_args = array( 'before_widget' => $before_widget, 'after_widget' => "</div>", 'before_title' => '<h2 class="widgettitle">', 'after_title' => '</h2>' );
+	$default_args = array(
+		'before_widget' => '<div class="widget %s">',
+		'after_widget'  => "</div>",
+		'before_title'  => '<h2 class="widgettitle">',
+		'after_title'   => '</h2>',
+	);
+	$args = wp_parse_args( $args, $default_args );
+	$args['before_widget'] = sprintf( $args['before_widget'], $widget_obj->widget_options['classname'] );
 
-	$args = wp_parse_args($args, $default_args);
 	$instance = wp_parse_args($instance);
 
 	/**
@@ -1585,9 +1087,14 @@
 }
 
 /**
- * Private
+ * Retrieves the widget ID base value.
+ *
+ * @since 2.8.0
+ *
+ * @param string $id Widget ID.
+ * @return string Widget ID base.
  */
-function _get_widget_id_base($id) {
+function _get_widget_id_base( $id ) {
 	return preg_replace( '/-[0-9]+$/', '', $id );
 }
 
@@ -1596,6 +1103,8 @@
  *
  * @access private
  * @since 3.3.0
+ *
+ * @global array $sidebars_widgets
  */
 function _wp_sidebars_changed() {
 	global $sidebars_widgets;
@@ -1611,110 +1120,531 @@
  *
  * @since 2.8.0
  *
+ * @global array $wp_registered_sidebars
+ * @global array $sidebars_widgets
+ * @global array $wp_registered_widgets
+ *
  * @param string|bool $theme_changed Whether the theme was changed as a boolean. A value
  *                                   of 'customize' defers updates for the Customizer.
- * @return array
+ * @return array Updated sidebars widgets.
  */
 function retrieve_widgets( $theme_changed = false ) {
 	global $wp_registered_sidebars, $sidebars_widgets, $wp_registered_widgets;
 
-	$registered_sidebar_keys = array_keys( $wp_registered_sidebars );
-	$orphaned = 0;
-
-	$old_sidebars_widgets = get_theme_mod( 'sidebars_widgets' );
-	if ( is_array( $old_sidebars_widgets ) ) {
-		// time() that sidebars were stored is in $old_sidebars_widgets['time']
-		$_sidebars_widgets = $old_sidebars_widgets['data'];
-
-		if ( 'customize' !== $theme_changed ) {
-			remove_theme_mod( 'sidebars_widgets' );
-		}
+	$registered_sidebars_keys = array_keys( $wp_registered_sidebars );
+	$registered_widgets_ids   = array_keys( $wp_registered_widgets );
 
-		foreach ( $_sidebars_widgets as $sidebar => $widgets ) {
-			if ( 'wp_inactive_widgets' === $sidebar || 'orphaned_widgets' === substr( $sidebar, 0, 16 ) ) {
-				continue;
-			}
-
-			if ( !in_array( $sidebar, $registered_sidebar_keys ) ) {
-				$_sidebars_widgets['orphaned_widgets_' . ++$orphaned] = $widgets;
-				unset( $_sidebars_widgets[$sidebar] );
-			}
+	if ( ! is_array( get_theme_mod( 'sidebars_widgets' ) ) )  {
+		if ( empty( $sidebars_widgets ) ) {
+			return array();
 		}
-	} else {
-		if ( empty( $sidebars_widgets ) )
-			return;
 
 		unset( $sidebars_widgets['array_version'] );
 
-		$old = array_keys($sidebars_widgets);
-		sort($old);
-		sort($registered_sidebar_keys);
-
-		if ( $old == $registered_sidebar_keys )
-			return;
-
-		$_sidebars_widgets = array(
-			'wp_inactive_widgets' => !empty( $sidebars_widgets['wp_inactive_widgets'] ) ? $sidebars_widgets['wp_inactive_widgets'] : array()
-		);
-
-		unset( $sidebars_widgets['wp_inactive_widgets'] );
+		$sidebars_widgets_keys = array_keys( $sidebars_widgets );
+		sort( $sidebars_widgets_keys );
+		sort( $registered_sidebars_keys );
 
-		foreach ( $wp_registered_sidebars as $id => $settings ) {
-			if ( $theme_changed ) {
-				$_sidebars_widgets[$id] = array_shift( $sidebars_widgets );
-			} else {
-				// no theme change, grab only sidebars that are currently registered
-				if ( isset( $sidebars_widgets[$id] ) ) {
-					$_sidebars_widgets[$id] = $sidebars_widgets[$id];
-					unset( $sidebars_widgets[$id] );
-				}
-			}
-		}
+		if ( $sidebars_widgets_keys === $registered_sidebars_keys ) {
+			$sidebars_widgets = _wp_remove_unregistered_widgets( $sidebars_widgets, $registered_widgets_ids );
 
-		foreach ( $sidebars_widgets as $val ) {
-			if ( is_array($val) && ! empty( $val ) )
-				$_sidebars_widgets['orphaned_widgets_' . ++$orphaned] = $val;
+			return $sidebars_widgets;
 		}
 	}
 
-	// discard invalid, theme-specific widgets from sidebars
-	$shown_widgets = array();
-
-	foreach ( $_sidebars_widgets as $sidebar => $widgets ) {
-		if ( !is_array($widgets) )
-			continue;
+	// Discard invalid, theme-specific widgets from sidebars.
+	$sidebars_widgets = _wp_remove_unregistered_widgets( $sidebars_widgets, $registered_widgets_ids );
+	$sidebars_widgets = wp_map_sidebars_widgets( $sidebars_widgets );
 
-		$_widgets = array();
-		foreach ( $widgets as $widget ) {
-			if ( isset($wp_registered_widgets[$widget]) )
-				$_widgets[] = $widget;
-		}
-
-		$_sidebars_widgets[$sidebar] = $_widgets;
-		$shown_widgets = array_merge($shown_widgets, $_widgets);
-	}
+	// Find hidden/lost multi-widget instances.
+	$shown_widgets = call_user_func_array( 'array_merge', $sidebars_widgets );
+	$lost_widgets  = array_diff( $registered_widgets_ids, $shown_widgets );
 
-	$sidebars_widgets = $_sidebars_widgets;
-	unset($_sidebars_widgets, $_widgets);
-
-	// find hidden/lost multi-widget instances
-	$lost_widgets = array();
-	foreach ( $wp_registered_widgets as $key => $val ) {
-		if ( in_array($key, $shown_widgets, true) )
-			continue;
+	foreach ( $lost_widgets as $key => $widget_id ) {
+		$number = preg_replace( '/.+?-([0-9]+)$/', '$1', $widget_id );
 
-		$number = preg_replace('/.+?-([0-9]+)$/', '$1', $key);
-
-		if ( 2 > (int) $number )
-			continue;
+		// Only keep active and default widgets.
+		if ( is_numeric( $number ) && (int) $number < 2 ) {
+			unset( $lost_widgets[ $key ] );
+		}
+	}
+	$sidebars_widgets['wp_inactive_widgets'] = array_merge( $lost_widgets, (array) $sidebars_widgets['wp_inactive_widgets'] );
 
-		$lost_widgets[] = $key;
-	}
-
-	$sidebars_widgets['wp_inactive_widgets'] = array_merge($lost_widgets, (array) $sidebars_widgets['wp_inactive_widgets']);
 	if ( 'customize' !== $theme_changed ) {
 		wp_set_sidebars_widgets( $sidebars_widgets );
 	}
 
 	return $sidebars_widgets;
 }
+
+/**
+ * Compares a list of sidebars with their widgets against a whitelist.
+ *
+ * @since 4.9.0
+ * @since 4.9.2 Always tries to restore widget assignments from previous data, not just if sidebars needed mapping.
+ *
+ * @param array $existing_sidebars_widgets List of sidebars and their widget instance IDs.
+ * @return array Mapped sidebars widgets.
+ */
+function wp_map_sidebars_widgets( $existing_sidebars_widgets ) {
+	global $wp_registered_sidebars;
+
+	$new_sidebars_widgets = array(
+		'wp_inactive_widgets' => array(),
+	);
+
+	// Short-circuit if there are no sidebars to map.
+	if ( ! is_array( $existing_sidebars_widgets ) || empty( $existing_sidebars_widgets ) ) {
+		return $new_sidebars_widgets;
+	}
+
+	foreach ( $existing_sidebars_widgets as $sidebar => $widgets ) {
+		if ( 'wp_inactive_widgets' === $sidebar || 'orphaned_widgets' === substr( $sidebar, 0, 16 ) ) {
+			$new_sidebars_widgets['wp_inactive_widgets'] = array_merge( $new_sidebars_widgets['wp_inactive_widgets'], (array) $widgets );
+			unset( $existing_sidebars_widgets[ $sidebar ] );
+		}
+	}
+
+	// If old and new theme have just one sidebar, map it and we're done.
+	if ( 1 === count( $existing_sidebars_widgets ) && 1 === count( $wp_registered_sidebars ) ) {
+		$new_sidebars_widgets[ key( $wp_registered_sidebars ) ] = array_pop( $existing_sidebars_widgets );
+
+		return $new_sidebars_widgets;
+	}
+
+	// Map locations with the same slug.
+	$existing_sidebars = array_keys( $existing_sidebars_widgets );
+
+	foreach ( $wp_registered_sidebars as $sidebar => $name ) {
+		if ( in_array( $sidebar, $existing_sidebars, true ) ) {
+			$new_sidebars_widgets[ $sidebar ] = $existing_sidebars_widgets[ $sidebar ];
+			unset( $existing_sidebars_widgets[ $sidebar ] );
+		} else if ( ! array_key_exists( $sidebar, $new_sidebars_widgets ) ) {
+			$new_sidebars_widgets[ $sidebar ] = array();
+		}
+	}
+
+	// If there are more sidebars, try to map them.
+	if ( ! empty( $existing_sidebars_widgets ) ) {
+
+		/*
+		 * If old and new theme both have sidebars that contain phrases
+		 * from within the same group, make an educated guess and map it.
+		 */
+		$common_slug_groups = array(
+			array( 'sidebar', 'primary', 'main', 'right' ),
+			array( 'second', 'left' ),
+			array( 'sidebar-2', 'footer', 'bottom' ),
+			array( 'header', 'top' ),
+		);
+
+		// Go through each group...
+		foreach ( $common_slug_groups as $slug_group ) {
+
+			// ...and see if any of these slugs...
+			foreach ( $slug_group as $slug ) {
+
+				// ...and any of the new sidebars...
+				foreach ( $wp_registered_sidebars as $new_sidebar => $args ) {
+
+					// ...actually match!
+					if ( false === stripos( $new_sidebar, $slug ) && false === stripos( $slug, $new_sidebar ) ) {
+						continue;
+					}
+
+					// Then see if any of the existing sidebars...
+					foreach ( $existing_sidebars_widgets as $sidebar => $widgets ) {
+
+						// ...and any slug in the same group...
+						foreach ( $slug_group as $slug ) {
+
+							// ... have a match as well.
+							if ( false === stripos( $sidebar, $slug ) && false === stripos( $slug, $sidebar ) ) {
+								continue;
+							}
+
+							// Make sure this sidebar wasn't mapped and removed previously.
+							if ( ! empty( $existing_sidebars_widgets[ $sidebar ] ) ) {
+
+								// We have a match that can be mapped!
+								$new_sidebars_widgets[ $new_sidebar ] = array_merge( $new_sidebars_widgets[ $new_sidebar ], $existing_sidebars_widgets[ $sidebar ] );
+
+								// Remove the mapped sidebar so it can't be mapped again.
+								unset( $existing_sidebars_widgets[ $sidebar ] );
+
+								// Go back and check the next new sidebar.
+								continue 3;
+							}
+						} // endforeach ( $slug_group as $slug )
+					} // endforeach ( $existing_sidebars_widgets as $sidebar => $widgets )
+				} // endforeach foreach ( $wp_registered_sidebars as $new_sidebar => $args )
+			} // endforeach ( $slug_group as $slug )
+		} // endforeach ( $common_slug_groups as $slug_group )
+	}
+
+	// Move any left over widgets to inactive sidebar.
+	foreach ( $existing_sidebars_widgets as $widgets ) {
+		if ( is_array( $widgets ) && ! empty( $widgets ) ) {
+			$new_sidebars_widgets['wp_inactive_widgets'] = array_merge( $new_sidebars_widgets['wp_inactive_widgets'], $widgets );
+		}
+	}
+
+	// Sidebars_widgets settings from when this theme was previously active.
+	$old_sidebars_widgets = get_theme_mod( 'sidebars_widgets' );
+	$old_sidebars_widgets = isset( $old_sidebars_widgets['data'] ) ? $old_sidebars_widgets['data'] : false;
+
+	if ( is_array( $old_sidebars_widgets ) ) {
+
+		// Remove empty sidebars, no need to map those.
+		$old_sidebars_widgets = array_filter( $old_sidebars_widgets );
+
+		// Only check sidebars that are empty or have not been mapped to yet.
+		foreach ( $new_sidebars_widgets as $new_sidebar => $new_widgets ) {
+			if ( array_key_exists( $new_sidebar, $old_sidebars_widgets ) && ! empty( $new_widgets ) ) {
+				unset( $old_sidebars_widgets[ $new_sidebar ] );
+			}
+		}
+
+		// Remove orphaned widgets, we're only interested in previously active sidebars.
+		foreach ( $old_sidebars_widgets as $sidebar => $widgets ) {
+			if ( 'orphaned_widgets' === substr( $sidebar, 0, 16 ) ) {
+				unset( $old_sidebars_widgets[ $sidebar ] );
+			}
+		}
+
+		$old_sidebars_widgets = _wp_remove_unregistered_widgets( $old_sidebars_widgets );
+
+		if ( ! empty( $old_sidebars_widgets ) ) {
+
+			// Go through each remaining sidebar...
+			foreach ( $old_sidebars_widgets as $old_sidebar => $old_widgets ) {
+
+				// ...and check every new sidebar...
+				foreach ( $new_sidebars_widgets as $new_sidebar => $new_widgets ) {
+
+					// ...for every widget we're trying to revive.
+					foreach ( $old_widgets as $key => $widget_id ) {
+						$active_key = array_search( $widget_id, $new_widgets, true );
+
+						// If the widget is used elsewhere...
+						if ( false !== $active_key ) {
+
+							// ...and that elsewhere is inactive widgets...
+							if ( 'wp_inactive_widgets' === $new_sidebar ) {
+
+								// ...remove it from there and keep the active version...
+								unset( $new_sidebars_widgets['wp_inactive_widgets'][ $active_key ] );
+							} else {
+
+								// ...otherwise remove it from the old sidebar and keep it in the new one.
+								unset( $old_sidebars_widgets[ $old_sidebar ][ $key ] );
+							}
+						} // endif ( $active_key )
+					} // endforeach ( $old_widgets as $key => $widget_id )
+				} // endforeach ( $new_sidebars_widgets as $new_sidebar => $new_widgets )
+			} // endforeach ( $old_sidebars_widgets as $old_sidebar => $old_widgets )
+		} // endif ( ! empty( $old_sidebars_widgets ) )
+
+
+		// Restore widget settings from when theme was previously active.
+		$new_sidebars_widgets = array_merge( $new_sidebars_widgets, $old_sidebars_widgets );
+	}
+
+	return $new_sidebars_widgets;
+}
+
+/**
+ * Compares a list of sidebars with their widgets against a whitelist.
+ *
+ * @since 4.9.0
+ *
+ * @param array $sidebars_widgets List of sidebars and their widget instance IDs.
+ * @param array $whitelist        Optional. List of widget IDs to compare against. Default: Registered widgets.
+ * @return array Sidebars with whitelisted widgets.
+ */
+function _wp_remove_unregistered_widgets( $sidebars_widgets, $whitelist = array() ) {
+	if ( empty( $whitelist ) ) {
+		$whitelist = array_keys( $GLOBALS['wp_registered_widgets'] );
+	}
+
+	foreach ( $sidebars_widgets as $sidebar => $widgets ) {
+		if ( is_array( $widgets ) ) {
+			$sidebars_widgets[ $sidebar ] = array_intersect( $widgets, $whitelist );
+		}
+	}
+
+	return $sidebars_widgets;
+}
+
+/**
+ * Display the RSS entries in a list.
+ *
+ * @since 2.5.0
+ *
+ * @param string|array|object $rss RSS url.
+ * @param array $args Widget arguments.
+ */
+function wp_widget_rss_output( $rss, $args = array() ) {
+	if ( is_string( $rss ) ) {
+		$rss = fetch_feed($rss);
+	} elseif ( is_array($rss) && isset($rss['url']) ) {
+		$args = $rss;
+		$rss = fetch_feed($rss['url']);
+	} elseif ( !is_object($rss) ) {
+		return;
+	}
+
+	if ( is_wp_error($rss) ) {
+		if ( is_admin() || current_user_can('manage_options') )
+			echo '<p><strong>' . __( 'RSS Error:' ) . '</strong> ' . $rss->get_error_message() . '</p>';
+		return;
+	}
+
+	$default_args = array( 'show_author' => 0, 'show_date' => 0, 'show_summary' => 0, 'items' => 0 );
+	$args = wp_parse_args( $args, $default_args );
+
+	$items = (int) $args['items'];
+	if ( $items < 1 || 20 < $items )
+		$items = 10;
+	$show_summary  = (int) $args['show_summary'];
+	$show_author   = (int) $args['show_author'];
+	$show_date     = (int) $args['show_date'];
+
+	if ( !$rss->get_item_quantity() ) {
+		echo '<ul><li>' . __( 'An error has occurred, which probably means the feed is down. Try again later.' ) . '</li></ul>';
+		$rss->__destruct();
+		unset($rss);
+		return;
+	}
+
+	echo '<ul>';
+	foreach ( $rss->get_items( 0, $items ) as $item ) {
+		$link = $item->get_link();
+		while ( stristr( $link, 'http' ) != $link ) {
+			$link = substr( $link, 1 );
+		}
+		$link = esc_url( strip_tags( $link ) );
+
+		$title = esc_html( trim( strip_tags( $item->get_title() ) ) );
+		if ( empty( $title ) ) {
+			$title = __( 'Untitled' );
+		}
+
+		$desc = @html_entity_decode( $item->get_description(), ENT_QUOTES, get_option( 'blog_charset' ) );
+		$desc = esc_attr( wp_trim_words( $desc, 55, ' [&hellip;]' ) );
+
+		$summary = '';
+		if ( $show_summary ) {
+			$summary = $desc;
+
+			// Change existing [...] to [&hellip;].
+			if ( '[...]' == substr( $summary, -5 ) ) {
+				$summary = substr( $summary, 0, -5 ) . '[&hellip;]';
+			}
+
+			$summary = '<div class="rssSummary">' . esc_html( $summary ) . '</div>';
+		}
+
+		$date = '';
+		if ( $show_date ) {
+			$date = $item->get_date( 'U' );
+
+			if ( $date ) {
+				$date = ' <span class="rss-date">' . date_i18n( get_option( 'date_format' ), $date ) . '</span>';
+			}
+		}
+
+		$author = '';
+		if ( $show_author ) {
+			$author = $item->get_author();
+			if ( is_object($author) ) {
+				$author = $author->get_name();
+				$author = ' <cite>' . esc_html( strip_tags( $author ) ) . '</cite>';
+			}
+		}
+
+		if ( $link == '' ) {
+			echo "<li>$title{$date}{$summary}{$author}</li>";
+		} elseif ( $show_summary ) {
+			echo "<li><a class='rsswidget' href='$link'>$title</a>{$date}{$summary}{$author}</li>";
+		} else {
+			echo "<li><a class='rsswidget' href='$link'>$title</a>{$date}{$author}</li>";
+		}
+	}
+	echo '</ul>';
+	$rss->__destruct();
+	unset($rss);
+}
+
+/**
+ * Display RSS widget options form.
+ *
+ * The options for what fields are displayed for the RSS form are all booleans
+ * and are as follows: 'url', 'title', 'items', 'show_summary', 'show_author',
+ * 'show_date'.
+ *
+ * @since 2.5.0
+ *
+ * @param array|string $args Values for input fields.
+ * @param array $inputs Override default display options.
+ */
+function wp_widget_rss_form( $args, $inputs = null ) {
+	$default_inputs = array( 'url' => true, 'title' => true, 'items' => true, 'show_summary' => true, 'show_author' => true, 'show_date' => true );
+	$inputs = wp_parse_args( $inputs, $default_inputs );
+
+	$args['title'] = isset( $args['title'] ) ? $args['title'] : '';
+	$args['url'] = isset( $args['url'] ) ? $args['url'] : '';
+	$args['items'] = isset( $args['items'] ) ? (int) $args['items'] : 0;
+
+	if ( $args['items'] < 1 || 20 < $args['items'] ) {
+		$args['items'] = 10;
+	}
+
+	$args['show_summary']   = isset( $args['show_summary'] ) ? (int) $args['show_summary'] : (int) $inputs['show_summary'];
+	$args['show_author']    = isset( $args['show_author'] ) ? (int) $args['show_author'] : (int) $inputs['show_author'];
+	$args['show_date']      = isset( $args['show_date'] ) ? (int) $args['show_date'] : (int) $inputs['show_date'];
+
+	if ( ! empty( $args['error'] ) ) {
+		echo '<p class="widget-error"><strong>' . __( 'RSS Error:' ) . '</strong> ' . $args['error'] . '</p>';
+	}
+
+	$esc_number = esc_attr( $args['number'] );
+	if ( $inputs['url'] ) :
+?>
+	<p><label for="rss-url-<?php echo $esc_number; ?>"><?php _e( 'Enter the RSS feed URL here:' ); ?></label>
+	<input class="widefat" id="rss-url-<?php echo $esc_number; ?>" name="widget-rss[<?php echo $esc_number; ?>][url]" type="text" value="<?php echo esc_url( $args['url'] ); ?>" /></p>
+<?php endif; if ( $inputs['title'] ) : ?>
+	<p><label for="rss-title-<?php echo $esc_number; ?>"><?php _e( 'Give the feed a title (optional):' ); ?></label>
+	<input class="widefat" id="rss-title-<?php echo $esc_number; ?>" name="widget-rss[<?php echo $esc_number; ?>][title]" type="text" value="<?php echo esc_attr( $args['title'] ); ?>" /></p>
+<?php endif; if ( $inputs['items'] ) : ?>
+	<p><label for="rss-items-<?php echo $esc_number; ?>"><?php _e( 'How many items would you like to display?' ); ?></label>
+	<select id="rss-items-<?php echo $esc_number; ?>" name="widget-rss[<?php echo $esc_number; ?>][items]">
+	<?php
+	for ( $i = 1; $i <= 20; ++$i ) {
+		echo "<option value='$i' " . selected( $args['items'], $i, false ) . ">$i</option>";
+	}
+	?>
+	</select></p>
+<?php endif; if ( $inputs['show_summary'] ) : ?>
+	<p><input id="rss-show-summary-<?php echo $esc_number; ?>" name="widget-rss[<?php echo $esc_number; ?>][show_summary]" type="checkbox" value="1" <?php checked( $args['show_summary'] ); ?> />
+	<label for="rss-show-summary-<?php echo $esc_number; ?>"><?php _e( 'Display item content?' ); ?></label></p>
+<?php endif; if ( $inputs['show_author'] ) : ?>
+	<p><input id="rss-show-author-<?php echo $esc_number; ?>" name="widget-rss[<?php echo $esc_number; ?>][show_author]" type="checkbox" value="1" <?php checked( $args['show_author'] ); ?> />
+	<label for="rss-show-author-<?php echo $esc_number; ?>"><?php _e( 'Display item author if available?' ); ?></label></p>
+<?php endif; if ( $inputs['show_date'] ) : ?>
+	<p><input id="rss-show-date-<?php echo $esc_number; ?>" name="widget-rss[<?php echo $esc_number; ?>][show_date]" type="checkbox" value="1" <?php checked( $args['show_date'] ); ?>/>
+	<label for="rss-show-date-<?php echo $esc_number; ?>"><?php _e( 'Display item date?' ); ?></label></p>
+<?php
+	endif;
+	foreach ( array_keys($default_inputs) as $input ) :
+		if ( 'hidden' === $inputs[$input] ) :
+			$id = str_replace( '_', '-', $input );
+?>
+	<input type="hidden" id="rss-<?php echo esc_attr( $id ); ?>-<?php echo $esc_number; ?>" name="widget-rss[<?php echo $esc_number; ?>][<?php echo esc_attr( $input ); ?>]" value="<?php echo esc_attr( $args[ $input ] ); ?>" />
+<?php
+		endif;
+	endforeach;
+}
+
+/**
+ * Process RSS feed widget data and optionally retrieve feed items.
+ *
+ * The feed widget can not have more than 20 items or it will reset back to the
+ * default, which is 10.
+ *
+ * The resulting array has the feed title, feed url, feed link (from channel),
+ * feed items, error (if any), and whether to show summary, author, and date.
+ * All respectively in the order of the array elements.
+ *
+ * @since 2.5.0
+ *
+ * @param array $widget_rss RSS widget feed data. Expects unescaped data.
+ * @param bool $check_feed Optional, default is true. Whether to check feed for errors.
+ * @return array
+ */
+function wp_widget_rss_process( $widget_rss, $check_feed = true ) {
+	$items = (int) $widget_rss['items'];
+	if ( $items < 1 || 20 < $items )
+		$items = 10;
+	$url           = esc_url_raw( strip_tags( $widget_rss['url'] ) );
+	$title         = isset( $widget_rss['title'] ) ? trim( strip_tags( $widget_rss['title'] ) ) : '';
+	$show_summary  = isset( $widget_rss['show_summary'] ) ? (int) $widget_rss['show_summary'] : 0;
+	$show_author   = isset( $widget_rss['show_author'] ) ? (int) $widget_rss['show_author'] :0;
+	$show_date     = isset( $widget_rss['show_date'] ) ? (int) $widget_rss['show_date'] : 0;
+
+	if ( $check_feed ) {
+		$rss = fetch_feed($url);
+		$error = false;
+		$link = '';
+		if ( is_wp_error($rss) ) {
+			$error = $rss->get_error_message();
+		} else {
+			$link = esc_url(strip_tags($rss->get_permalink()));
+			while ( stristr($link, 'http') != $link )
+				$link = substr($link, 1);
+
+			$rss->__destruct();
+			unset($rss);
+		}
+	}
+
+	return compact( 'title', 'url', 'link', 'items', 'error', 'show_summary', 'show_author', 'show_date' );
+}
+
+/**
+ * Registers all of the default WordPress widgets on startup.
+ *
+ * Calls {@see 'widgets_init'} action after all of the WordPress widgets have been registered.
+ *
+ * @since 2.2.0
+ */
+function wp_widgets_init() {
+	if ( ! is_blog_installed() ) {
+		return;
+	}
+
+	register_widget( 'WP_Widget_Pages' );
+
+	register_widget( 'WP_Widget_Calendar' );
+
+	register_widget( 'WP_Widget_Archives' );
+
+	if ( get_option( 'link_manager_enabled' ) ) {
+		register_widget( 'WP_Widget_Links' );
+	}
+
+	register_widget( 'WP_Widget_Media_Audio' );
+
+	register_widget( 'WP_Widget_Media_Image' );
+
+	register_widget( 'WP_Widget_Media_Gallery' );
+
+	register_widget( 'WP_Widget_Media_Video' );
+
+	register_widget( 'WP_Widget_Meta' );
+
+	register_widget( 'WP_Widget_Search' );
+
+	register_widget( 'WP_Widget_Text' );
+
+	register_widget( 'WP_Widget_Categories' );
+
+	register_widget( 'WP_Widget_Recent_Posts' );
+
+	register_widget( 'WP_Widget_Recent_Comments' );
+
+	register_widget( 'WP_Widget_RSS' );
+
+	register_widget( 'WP_Widget_Tag_Cloud' );
+
+	register_widget( 'WP_Nav_Menu_Widget' );
+
+	register_widget( 'WP_Widget_Custom_HTML' );
+
+	/**
+	 * Fires after all default WordPress widgets have been registered.
+	 *
+	 * @since 2.2.0
+	 */
+	do_action( 'widgets_init' );
+}