API Deprecate API that will be removed as a result of refactoring

src/Controller/SubsiteXHRController.php

@@ -4,6 +4,7 @@
 
 use SilverStripe\Admin\LeftAndMain;
 use SilverStripe\Control\PjaxResponseNegotiator;
+use SilverStripe\Dev\Deprecation;
 use SilverStripe\Security\Member;
 use SilverStripe\Security\Permission;
 use SilverStripe\Subsites\Model\Subsite;
@@ -37,9 +38,11 @@ public function canView($member = null)
 
     /**
      * Allow access if user allowed into the CMS at all.
+     * @deprecated 3.4.0 Will be removed without equivalent functionality to replace it.
      */
     public function canAccess()
     {
+        Deprecation::noticeWithNoReplacment('3.4.0');
         // Allow if any cms access is available
         return Permission::check([
             'CMS_ACCESS', // Supported by 3.1.14 and up

src/Extensions/LeftAndMainSubsites.php

@@ -13,9 +13,11 @@
 use SilverStripe\Control\Controller;
 use SilverStripe\Core\Config\Config;
 use SilverStripe\Core\Convert;
+use SilverStripe\Dev\Deprecation;
 use SilverStripe\Forms\HiddenField;
 use SilverStripe\ORM\ArrayList;
 use SilverStripe\ORM\DataObject;
+use SilverStripe\ORM\SS_List;
 use SilverStripe\Security\Member;
 use SilverStripe\Security\Permission;
 use SilverStripe\Security\Security;
@@ -24,13 +26,14 @@
 use SilverStripe\Subsites\State\SubsiteState;
 use SilverStripe\View\ArrayData;
 use SilverStripe\View\Requirements;
+use SilverStripe\View\TemplateGlobalProvider;
 
 /**
  * Decorator designed to add subsites support to LeftAndMain
  *
  * @extends LeftAndMainExtension<LeftAndMain>
  */
-class LeftAndMainSubsites extends LeftAndMainExtension
+class LeftAndMainSubsites extends LeftAndMainExtension implements TemplateGlobalProvider
 {
     private static $allowed_actions = ['CopyToSubsite'];
 
@@ -47,6 +50,44 @@ public function init()
         Requirements::javascript('silverstripe/subsites:client/dist/js/LeftAndMain_Subsites.js');
     }
 
+    public static function get_template_global_variables()
+    {
+        return [
+            'SubsiteSwitchList',
+        ];
+    }
+
+    /**
+     * Generates a list of subsites with the data needed to
+     * produce a dropdown site switcher
+     * @return SS_List<Subsite>
+     */
+    public static function SubsiteSwitchList(): SS_List
+    {
+        $list = Subsite::all_accessible_sites();
+        $currentSubsiteID = SubsiteState::singleton()->getSubsiteId();
+
+        if ($list == null || $list->count() == 1 && $list->first()->DefaultSite == true) {
+            return false;
+        }
+
+        Requirements::javascript('silverstripe/subsites:client/dist/js/LeftAndMain_Subsites.js');
+
+        $output = ArrayList::create();
+
+        foreach ($list as $subsite) {
+            $currentState = $subsite->ID == $currentSubsiteID ? 'selected' : '';
+
+            $output->push(ArrayData::create([
+                'CurrentState' => $currentState,
+                'ID' => $subsite->ID,
+                'Title' => $subsite->Title,
+            ]));
+        }
+
+        return $output;
+    }
+
     /**
      * Set the title of the CMS tree
      */
@@ -145,31 +186,12 @@ public function Subsites()
      * Generates a list of subsites with the data needed to
      * produce a dropdown site switcher
      * @return ArrayList<Subsite>
+     * @deprecated 3.4.0 Will be removed without equivalent functionality to replace it.
      */
     public function ListSubsites()
     {
-        $list = $this->Subsites();
-        $currentSubsiteID = SubsiteState::singleton()->getSubsiteId();
-
-        if ($list == null || $list->count() == 1 && $list->first()->DefaultSite == true) {
-            return false;
-        }
-
-        Requirements::javascript('silverstripe/subsites:client/dist/js/LeftAndMain_Subsites.js');
-
-        $output = ArrayList::create();
-
-        foreach ($list as $subsite) {
-            $currentState = $subsite->ID == $currentSubsiteID ? 'selected' : '';
-
-            $output->push(ArrayData::create([
-                'CurrentState' => $currentState,
-                'ID' => $subsite->ID,
-                'Title' => $subsite->Title,
-            ]));
-        }
-
-        return $output;
+        Deprecation::notice('3.4.0', 'Use SubsiteSwitchList() instead.');
+        return static::SubsiteSwitchList();
     }
 
     public function alternateMenuDisplayCheck($controllerName)

templates/SilverStripe/Admin/LeftAndMain_Menu.ss

@@ -5,7 +5,7 @@
         <% include SilverStripe\\Admin\\LeftAndMain_MenuLogo %>
         <% include SilverStripe\\Admin\\LeftAndMain_MenuStatus %>
 
-        <% if $ListSubsites.Count > 1 %>
+        <% if $SubsiteSwitchList.Count > 1 %>
             <% include SilverStripe\\Subsites\\Controller\\SubsiteXHRController_subsitelist %>
         <% end_if %>
     </div>

templates/SilverStripe/Subsites/Controller/Includes/SubsiteXHRController_subsitelist.ss

@@ -1,7 +1,7 @@
 <div class="cms-subsites" data-pjax-fragment="SubsiteList">
 	<div class="field dropdown">
 		<select id="SubsitesSelect">
-			<% loop $ListSubsites %>
+			<% loop $SubsiteSwitchList %>
 				<option value="$ID" $CurrentState>$Title</option>
 			<% end_loop %>
 		</select>