Functions must not be nested

src/Libero/ruleset.xml

@@ -57,6 +57,7 @@
         </properties>
     </rule>
     <rule ref="Squiz.Classes.ClassFileName"/>
+    <rule ref="Squiz.PHP.InnerFunctions"/>
     <rule ref="Squiz.WhiteSpace.ObjectOperatorSpacing">
         <properties>
             <property name="ignoreNewlines" value="true"/>

tests/cases/functions/nested

@@ -0,0 +1,19 @@
+---DESCRIPTION---
+Functions must not be nested
+---CONTENTS---
+<?php
+
+declare(strict_types=1);
+
+namespace Vendor;
+
+function foo() : void
+{
+    function bar() : void
+    {
+    }
+}
+
+---MESSAGES---
+9:5 Squiz.PHP.InnerFunctions.NotAllowed
+---