Tell developers how to correctly silence `register_sidebar()` notices.

* If we just tell them they they should set an `id` parameter, they might set an arbitrary one on an existing (i.e. not in-development) theme, causing widgets to be lost.
* This way, we tell them to set it to the auto-generated `id` that the sidebar already has.
* Widget content is not lost, and now their sidebar has a concrete handle.

fixes #31675
Built from https://develop.svn.wordpress.org/trunk@32110


git-svn-id: http://core.svn.wordpress.org/trunk@32089 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.2-beta4-32109';
+$wp_version = '4.2-beta4-32110';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-includes/widgets.php

@@ -803,10 +803,7 @@ function register_sidebar($args = array()) {
 
 	$i = count($wp_registered_sidebars) + 1;
 
-	if ( empty( $args['id'] ) ) {
-		/* translators: %s: the id argument */
-		_doing_it_wrong( __FUNCTION__, sprintf( __( 'You should set %s in the arguments array.' ), '<code>id</code>' ), '4.2.0' );
-	}
+	$id_is_empty = empty( $args['id'] );
 
 	$defaults = array(
 		'name' => sprintf(__('Sidebar %d'), $i ),
@@ -821,6 +818,11 @@ function register_sidebar($args = array()) {
 
 	$sidebar = wp_parse_args( $args, $defaults );
 
+	if ( $id_is_empty ) {
+		/* translators: %1$s: the id argument */
+		_doing_it_wrong( __FUNCTION__, sprintf( __( 'No %1$s was set in the arguments array for the "%2$s" sidebar. Defaulting to "%3$s". Manually set the %1$s to  "%3$s" to silence this notice and keep existing sidebar content.' ), '<code>id</code>', $sidebar['name'], $sidebar['id'] ), '4.2.0' );
+	}
+
 	$wp_registered_sidebars[$sidebar['id']] = $sidebar;
 
 	add_theme_support('widgets');