Can't use inherited constant value via 'self' in enum case value

[wbars]

Description

The following code:

<?php

interface I {
    public const DEFAULT_VALUE = 'gambrinus';
}

enum Beer: string implements I {
    // case GAMBRINUS = I::DEFAULT_VALUE;
     case GAMBRINUS = self::DEFAULT_VALUE;
}
var_dump(Beer::GAMBRINUS);

Resulted in this output:

Fatal error: Enum case value must be compile-time evaluatable in /in/Oqm7f on line 9

But I expected this output instead:
No errors, because commented case GAMBRINUS = I::DEFAULT_VALUE produces no error

PHP Version

8.1.1

Operating System

No response

[wbars]

It seems I didn't fully understood compile-time semantics, can be closed.

[cmb69]

Not so fast; https://3v4l.org/5sZes works.

[nikic]

The problem here is that we compute a value to case table during compilation and all values must be known at that time. This happens pre-inheritance, so self::DEFAULT_VALUE is unknown at the time. This is unfortunate from a language design perspective, because what exactly can be evaluated during compilation and what can't is essentially an implementation detail (and may depend on whether opcache is used or not).

I think it should be possible to make this part of inheritance instead, which should allow us to evaluate all expressions. It would also delay some error reporting (about duplicate case values) to that point.