WP_Customize_Widgets::customize_register() WordPress Method

	public function customize_register() {
		global $wp_registered_widgets, $wp_registered_widget_controls, $wp_registered_sidebars;

		$use_widgets_block_editor = wp_use_widgets_block_editor();

		add_filter( 'sidebars_widgets', array( $this, 'preview_sidebars_widgets' ), 1 );

		$sidebars_widgets = array_merge(
			array( 'wp_inactive_widgets' => array() ),
			array_fill_keys( array_keys( $wp_registered_sidebars ), array() ),
			wp_get_sidebars_widgets()
		);

		$new_setting_ids = array();

		/*
		 * Register a setting for all widgets, including those which are active,
		 * inactive, and orphaned since a widget may get suppressed from a sidebar
		 * via a plugin (like Widget Visibility).
		 */
		foreach ( array_keys( $wp_registered_widgets ) as $widget_id ) {
			$setting_id   = $this->get_setting_id( $widget_id );
			$setting_args = $this->get_setting_args( $setting_id );
			if ( ! $this->manager->get_setting( $setting_id ) ) {
				$this->manager->add_setting( $setting_id, $setting_args );
			}
			$new_setting_ids[] = $setting_id;
		}

		/*
		 * Add a setting which will be supplied for the theme's sidebars_widgets
		 * theme_mod when the theme is switched.
		 */
		if ( ! $this->manager->is_theme_active() ) {
			$setting_id   = 'old_sidebars_widgets_data';
			$setting_args = $this->get_setting_args(
				$setting_id,
				array(
					'type'  => 'global_variable',
					'dirty' => true,
				)
			);
			$this->manager->add_setting( $setting_id, $setting_args );
		}

		$this->manager->add_panel(
			'widgets',
			array(
				'type'                     => 'widgets',
				'title'                    => __( 'Widgets' ),
				'description'              => __( 'Widgets are independent sections of content that can be placed into widgetized areas provided by your theme (commonly called sidebars).' ),
				'priority'                 => 110,
				'active_callback'          => array( $this, 'is_panel_active' ),
				'auto_expand_sole_section' => true,
				'theme_supports'           => 'widgets',
			)
		);

		foreach ( $sidebars_widgets as $sidebar_id => $sidebar_widget_ids ) {
			if ( empty( $sidebar_widget_ids ) ) {
				$sidebar_widget_ids = array();
			}

			$is_registered_sidebar = is_registered_sidebar( $sidebar_id );
			$is_inactive_widgets   = ( 'wp_inactive_widgets' === $sidebar_id );
			$is_active_sidebar     = ( $is_registered_sidebar && ! $is_inactive_widgets );

			// Add setting for managing the sidebar's widgets.
			if ( $is_registered_sidebar || $is_inactive_widgets ) {
				$setting_id   = sprintf( 'sidebars_widgets[%s]', $sidebar_id );
				$setting_args = $this->get_setting_args( $setting_id );
				if ( ! $this->manager->get_setting( $setting_id ) ) {
					if ( ! $this->manager->is_theme_active() ) {
						$setting_args['dirty'] = true;
					}
					$this->manager->add_setting( $setting_id, $setting_args );
				}
				$new_setting_ids[] = $setting_id;

				// Add section to contain controls.
				$section_id = sprintf( 'sidebar-widgets-%s', $sidebar_id );
				if ( $is_active_sidebar ) {

					$section_args = array(
						'title'      => $wp_registered_sidebars[ $sidebar_id ]['name'],
						'priority'   => array_search( $sidebar_id, array_keys( $wp_registered_sidebars ), true ),
						'panel'      => 'widgets',
						'sidebar_id' => $sidebar_id,
					);

					if ( $use_widgets_block_editor ) {
						$section_args['description'] = '';
					} else {
						$section_args['description'] = $wp_registered_sidebars[ $sidebar_id ]['description'];
					}

					/**
					 * Filters Customizer widget section arguments for a given sidebar.
					 *
					 * @since 3.9.0
					 *
					 * @param array      $section_args Array of Customizer widget section arguments.
					 * @param string     $section_id   Customizer section ID.
					 * @param int|string $sidebar_id   Sidebar ID.
					 */
					$section_args = apply_filters( 'customizer_widgets_section_args', $section_args, $section_id, $sidebar_id );

					$section = new WP_Customize_Sidebar_Section( $this->manager, $section_id, $section_args );
					$this->manager->add_section( $section );

					if ( $use_widgets_block_editor ) {
						$control = new WP_Sidebar_Block_Editor_Control(
							$this->manager,
							$setting_id,
							array(
								'section'     => $section_id,
								'sidebar_id'  => $sidebar_id,
								'label'       => $section_args['title'],
								'description' => $section_args['description'],
							)
						);
					} else {
						$control = new WP_Widget_Area_Customize_Control(
							$this->manager,
							$setting_id,
							array(
								'section'    => $section_id,
								'sidebar_id' => $sidebar_id,
								'priority'   => count( $sidebar_widget_ids ), // place 'Add Widget' and 'Reorder' buttons at end.
							)
						);
					}

					$this->manager->add_control( $control );

					$new_setting_ids[] = $setting_id;
				}
			}

			if ( ! $use_widgets_block_editor ) {
				// Add a control for each active widget (located in a sidebar).
				foreach ( $sidebar_widget_ids as $i => $widget_id ) {

					// Skip widgets that may have gone away due to a plugin being deactivated.
					if ( ! $is_active_sidebar || ! isset( $wp_registered_widgets[ $widget_id ] ) ) {
						continue;
					}

					$registered_widget = $wp_registered_widgets[ $widget_id ];
					$setting_id        = $this->get_setting_id( $widget_id );
					$id_base           = $wp_registered_widget_controls[ $widget_id ]['id_base'];

					$control = new WP_Widget_Form_Customize_Control(
						$this->manager,
						$setting_id,
						array(
							'label'          => $registered_widget['name'],
							'section'        => $section_id,
							'sidebar_id'     => $sidebar_id,
							'widget_id'      => $widget_id,
							'widget_id_base' => $id_base,
							'priority'       => $i,
							'width'          => $wp_registered_widget_controls[ $widget_id ]['width'],
							'height'         => $wp_registered_widget_controls[ $widget_id ]['height'],
							'is_wide'        => $this->is_wide_widget( $widget_id ),
						)
					);
					$this->manager->add_control( $control );
				}
			}
		}

		if ( $this->manager->settings_previewed() ) {
			foreach ( $new_setting_ids as $new_setting_id ) {
				$this->manager->get_setting( $new_setting_id )->preview();
			}
		}
	}