[5.4] Deprecate app property in FieldsPlugin (joomla#45695)

* [5.4] Deprecate app property in FieldsPlugin (Custom Fields)

Author: heelc29

administrator/components/com_fields/src/Plugin/FieldsPlugin.php

@@ -45,6 +45,8 @@ abstract class FieldsPlugin extends CMSPlugin
      *
      * @var    \Joomla\CMS\Application\CMSApplication
      * @since  4.0.0
+     *
+     * @deprecated  __DEPLOY_VERSION__ will be removed in 7.0 use $this->getApplication() instead
      */
     protected $app;
 
@@ -138,6 +140,7 @@ public function onCustomFieldsGetTypes()
             return $types_cache[$this->_type . $this->_name];
         }
 
+        $app   = $this->getApplication() ?: $this->app;
         $types = [];
 
         // The root of the plugin
@@ -160,11 +163,11 @@ public function onCustomFieldsGetTypes()
             // Needed attributes
             $data['type'] = $layout;
 
-            if ($this->app->getLanguage()->hasKey('PLG_FIELDS_' . $key . '_LABEL')) {
+            if ($app->getLanguage()->hasKey('PLG_FIELDS_' . $key . '_LABEL')) {
                 $data['label'] = Text::sprintf('PLG_FIELDS_' . $key . '_LABEL', strtolower($key));
 
                 // Fix wrongly set parentheses in RTL languages
-                if ($this->app->getLanguage()->isRtl()) {
+                if ($app->getLanguage()->isRtl()) {
                     $data['label'] .= '‎';
                 }
             } else {

phpstan-baseline.neon

@@ -2118,6 +2118,15 @@ parameters:
 			count: 1
 			path: administrator/components/com_fields/src/Model/GroupModel.php
 
+		-
+			message: '''
+				#^Access to deprecated property \$app of class Joomla\\Component\\Fields\\Administrator\\Plugin\\FieldsPlugin\:
+				__DEPLOY_VERSION__ will be removed in 7\.0 use \$this\-\>getApplication\(\) instead$#
+			'''
+			identifier: property.deprecated
+			count: 1
+			path: administrator/components/com_fields/src/Plugin/FieldsPlugin.php
+
 		-
 			message: '''
 				#^Call to deprecated method getUser\(\) of class Joomla\\CMS\\Factory\: