class.extendsInternalInterface

Code example

<?php declare(strict_types = 1);

namespace Vendor {
	/** @internal */
	interface InternalInterface {}
}

namespace App {
	class MyClass extends \Vendor\InternalInterface {}
}

Why is it reported?

The class extends a type that is marked as @internal. Internal types are not part of the package's public API and may change or be removed without notice in future versions.

A class cannot extend an interface in PHP -- it should use implements instead. This code is invalid regardless of the @internal annotation.

How to fix it

Use implements instead of extends, and use a non-internal interface:

-class MyClass extends \Vendor\InternalInterface {}
+class MyClass implements \Vendor\PublicInterface {}

If no public alternative exists, consider reaching out to the package maintainers to request a public API for your use case.