Icons.php error: watchout

Documentation/ApiOverview/Icon/Index.rst

@@ -38,6 +38,12 @@ The file needs to return a PHP configuration array with the following keys:
     :language: php
     :caption: EXT:my_extension/Configuration/Icons.php
 
+..  attention::
+    Do not overwrite the $icons variable in this file. This can lead to the error: 
+    "Fatal error: Uncaught Error: Call to a member function exchangeArray() on array in typo3/cms-core/Classes/Package/AbstractServiceProvider.php" 
+    (assuming you replaced the $icons variable with an array) 
+    :ref:`As with all .php files getting included by TYPO3, you should use a closure/anonymous function to encapsulate variables. <configuration_php_use_closures>`
+
 ..  index:: Icon API; IconProviderInterface
 
 Icon provider

Documentation/ExtensionArchitecture/BestPractises/ConfigurationFiles.rst

@@ -126,8 +126,38 @@ file with all configuration of other extensions.
     :php:`$_EXTKEY` option **must** be kept within an extension's
     :ref:`ext_emconf.php <extension-declaration>` file.
 
--   You **do not have to** use a directly called closure function after dropping
-    TYPO3 v10.4 support.
+
+..  _configuration_php_use_closures:
+
+Safety with Closures 
+====================
+You **do not have to** use a directly called closure function after dropping
+TYPO3 v10.4 support. But it is still recommended in other included files to 
+wrap them in a function.
+
+..  literalinclude:: _function_wrap.php
+    :language: php
+
+This is a list of those files where wrapping is still 
+recommended:
+
+-   ext_localconf.php (kinda fine since 8.7)
+-   ext_tables.php (kinda fine since 8.7)
+-   Configuration/RequestMiddlewares.php (fixed with 13.2)
+-   Configuration/Backend/Routes.php (fixed with 13.2)
+-   Configuration/Backend/AjaxRoutes.php (fixed with 13.2)
+-   Configuration/Backend/Modules.php (fixed with 13.2)
+-   Configuration/Backend/DashboardPresets.php (fixed with 13.2)
+-   Configuration/Backend/DashboardPresets.php (fixed with 13.2)
+-   Configuration/Backend/DashboardPresets.php (fixed with 13.2)
+-   Configuration/ContentSecurityPolicies.php (fixed with 13.2)
+-   Configuration/Icons.php (fixed with 13.2)
+-   Configuration/ExpressionLanguage.php
+-   Configuration/Backend/T3editor/Modes.php
+-   Configuration/Backend/T3editor/Addons.php
+-   Configuration/Extbase/Persistence/Classes.php
+-   ext_emconf.php (funnily here you have to overwrite the $EM_CONF variable)
+
 
 The following example contains the complete code:
 

Documentation/ExtensionArchitecture/BestPractises/_function_wrap.php

@@ -0,0 +1,9 @@
+<?php 
+return call_user_func(function () {
+    //code
+});
+//or
+$function = function () {
+    //code
+};
+return $function();