Customizer: Improve ability to filter active state for widget area Customizer sections.

* Mark panels, sections, controls as active if preview explicitly indicates.
* Introduce `WP_Customize_Sidebar_Section` PHP class, and `SidebarSection` JS class.
* Move logic for determining whether a sidebar section is active from the `SidebarControl` to `SidebarSection`.

props westonruter.
fixes #30235.

git-svn-id: https://develop.svn.wordpress.org/trunk@30329 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-customize-control.php

@@ -1115,17 +1115,6 @@ class WP_Widget_Area_Customize_Control extends WP_Customize_Control {
 		<?php
 	}
 
-	/**
-	 * Whether the current sidebar is rendered on the page.
-	 *
-	 * @since 4.0.0
-	 * @access public
-	 *
-	 * @return bool Whether sidebar is rendered.
-	 */
-	public function active_callback() {
-		return $this->manager->widgets->is_sidebar_rendered( $this->sidebar_id );
-	}
 }
 
 /**

src/wp-includes/class-wp-customize-manager.php

@@ -515,6 +515,9 @@ final class WP_Customize_Manager {
 		}
 		foreach ( $this->panels as $id => $panel ) {
 			$settings['activePanels'][ $id ] = $panel->active();
+			foreach ( $panel->sections as $id => $section ) {
+				$settings['activeSections'][ $id ] = $section->active();
+			}
 		}
 		foreach ( $this->sections as $id => $section ) {
 			$settings['activeSections'][ $id ] = $section->active();

src/wp-includes/class-wp-customize-section.php

@@ -310,3 +310,54 @@ class WP_Customize_Section {
 		<?php
 	}
 }
+
+/**
+ * Customizer section representing widget area (sidebar).
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.1.0
+ */
+class WP_Customize_Sidebar_Section extends WP_Customize_Section {
+
+	/**
+	 * @since 4.1.0
+	 * @access public
+	 * @var string
+	 */
+	public $type = 'sidebar';
+
+	/**
+	 * Unique identifier.
+	 *
+	 * @since 4.1.0
+	 * @access public
+	 * @var string
+	 */
+	public $sidebar_id;
+
+	/**
+	 * Gather the parameters passed to client JavaScript via JSON.
+	 *
+	 * @since 4.1.0
+	 *
+	 * @return array The array to be exported to the client as JSON
+	 */
+	public function json() {
+		$json = parent::json();
+		$json['sidebarId'] = $this->sidebar_id;
+		return $json;
+	}
+
+	/**
+	 * Whether the current sidebar is rendered on the page.
+	 *
+	 * @since 4.1.0
+	 * @access public
+	 *
+	 * @return bool Whether sidebar is rendered.
+	 */
+	public function active_callback() {
+		return $this->manager->widgets->is_sidebar_rendered( $this->sidebar_id );
+	}
+}

src/wp-includes/class-wp-customize-widgets.php

@@ -468,6 +468,7 @@ final class WP_Customize_Widgets {
 						'description' => $GLOBALS['wp_registered_sidebars'][ $sidebar_id ]['description'],
 						'priority' => array_search( $sidebar_id, array_keys( $wp_registered_sidebars ) ),
 						'panel' => 'widgets',
+						'sidebar_id' => $sidebar_id,
 					);
 
 					/**
@@ -481,7 +482,8 @@ final class WP_Customize_Widgets {
 					 */
 					$section_args = apply_filters( 'customizer_widgets_section_args', $section_args, $section_id, $sidebar_id );
 
-					$this->manager->add_section( $section_id, $section_args );
+					$section = new WP_Customize_Sidebar_Section( $this->manager, $section_id, $section_args );
+					$this->manager->add_section( $section );
 
 					$control = new WP_Widget_Area_Customize_Control( $this->manager, $setting_id, array(
 						'section'    => $section_id,