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MethodSignatureMustProvideReturnType

In PHP 8.1+, most non-final internal methods now require overriding methods to declare a compatible return type, otherwise a deprecated notice is emitted during inheritance validation.

This issue is emitted when a method overriding a native method is defined without a return type.

Only if the return type cannot be declared to keep support for PHP 7, a #[ReturnTypeWillChange] attribute can be added to silence the PHP deprecation notice and Psalm issue.

<?php
class A implements JsonSerializable {
    public function jsonSerialize() {
        return ['type' => 'A'];
    }
}