where is Class D ?

<?php
trait T {
        abstract static function values(): array;
}

//class B {
//      use T;
//      static function values() {
//              return 'Worked!'; // string, not array
//      }
//}

//echo B::valuesi(); // print: Worked!

abstract class B {
        use T;
        self::values(); // if inheritance trait, must implement abstract function in trait
}

class C extends B {
        static function values() {
                return 'Don\'t worked';
        }
}

echo C::values();

Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

This is expected behavior. In your first example, the abstract function from the trait is overriden by the function declared on your class. No inheritance rules are applied at all. It's not only about the return value type.

In your second example, you are importing the abstract function to an abstract class. In that case, the inheritance rules are applied when you are extending from that abstract class.

Actually, after re-reading the page on traits, the usage of abstract methods for this purpose is mentioned:

> Traits support the use of abstract methods in order to impose requirements upon the exhibiting class.

Given that, I am re-opening this bug.

I encountered this as well (discovered this report when filing my own bug, so I'm commenting here rather than filing a dupe). Note that this is in no way specific to static methods.

A similar reproduce case: https://3v4l.org/AVSXN

And more importantly, a test case where the issue that should have been detected at compile-time instead was left until runtime: https://3v4l.org/02d4a This is the main use-case of abstract trait methods.

There has been some discussion about this on the internals@
mailing list[1], and it seem to me that Levi[2] is right.
Therefore I'm changing this to a documentation problem.

[1] <https://externals.io/message/103032>
[2] <https://externals.io/message/103032#103039>

This bug has been fixed in the documentation's XML sources. Since the
online and downloadable versions of the documentation need some time
to get updated, we would like to ask you to be a bit patient.

Thank you for the report, and for helping us make our documentation better.