Incorrect #[Override] Attribute Usage Causes Error in PHP Trait Method

Minkwon

Description:
When a Trait containing a method with the #[Override] attribute is used within a class, an error message stating "no matching parent method exists" is displayed.

<?php

namespace My;

trait Top
{
    abstract public function topMethod(): void;
}

trait BarTrait
{
    use Top;

    #[\Override]
    public function topMethod(): void
    {
    }

    abstract public function barMethod(): void;
}

class Bar
{
    use BarTrait;

    #[\Override]
    public function barMethod(): void
    {
    }
}

$bar = new Bar();
$bar->topMethod();

JakubMisek

Thank you for the sample code.

Isn't that correct? Bar::topMethod() function is expected to override something.

Minkwon

JakubMisek

BarTrait includes use Top;, so it overrides topMethod().
Bar includes use BarTrait;, so it overrides barMethod().
So, I think Bar has no reason to override topMethod().

JakubMisek

I see, but that's not how traits and method overriding works.

Using a trait is not the same as extending a parent class, so the #[Override] attribute does not apply.

This is described in PHP's RFC: https://wiki.php.net/rfc/marking_overriden_methods, section Semantics:

The attribute is ignored on traits, but:

Methods from a used trait behave as if the method definition was copied and pasted into the target class. Specifically the #[\Override] attribute on a trait method requires the existence of a matching method in a parent class or implemented interface.

Additionally, in the sample above we should report barMethod() as an error as well.

Minkwon

JakubMisek
I see. Thank you.

JakubMisek

Minkwon Thank you for bringing this to my attention.

I've checked a few more code examples and improved the next version.