PHP 8.4: dynamic dispatch problem with traits and inheritance

[procodix]

Description

I have the following bug. I think it might by a corner case. It is very hard to narrow down. Please find this reduces example. In my real code many more traits are involved, as are promoted properties, property hooks, etc. I cannot pinpoint the error to a specific version, but Im sure, it worked correctly in PHP 8.3.

trait X {
    public function test() {echo 'this is from A';}
}

class A {
    use X;
}

class B extends A {
    public function test() {echo 'this is from B';}
}

class C extends B {
	public function run() {
		$this->test(); // this outputs 'this is from A' !!! 
	}
	
	// however if I include this function, it works correctly by echoing 'this is from B'
	// public function test() {
	// 	parent::test();
	// }

	// whats even more weird, is that an almost identical class D works correctly
}

So the call to C->test() skips the inherited B->test() and dispatches to A/X->test().

I ruled out, that

• a rouge "test" function exists, that takes over
• visibility problems with public
• a wrong class is used because of a namespace inaccuracy

Most interesting is, that the pure existence of the called method in C with an explicit call to the parent clears the issue. As this should be redundant, I assume a bug.

Please let me know, if I should provide more details. As it is very difficult to reduce the code to a non-working example, thought, maybe something changed in PHP 8.4 regarding dynamic dispatch which could lead to this behavior.

PHP Version

PHP 8.4

Operating System

macOS 15

[TimWolla]

I'm unable to reproduce the issue on https://3v4l.org/ejRtn.

Is the issue reliably appearing for you with the example script or is it happening randomly?

[procodix]

Thanks for the fast reply. The code is just a very condensed example, that abstracts the structure/problem. As soon as as I introduce the method in the class C it works. Removing it results in the erroneous call.

[nielsdos]

Do you have a reproducer or can you share the code where it happens in?
Also please answer the following questions:

• What is the exact PHP 8.4 version number that you use, there have been multiple 8.4 releases so far
• Does this happen with opcache on/off or both?
• Is the JIT involved?

[procodix]

PHP 8.4.5

• Opcode Caching | Up and Running
• Optimization | Enabled
• SHM Cache | Enabled
• File Cache | Disabled
• JIT | Disabled

I only noticed this in the code I'm currently working on. It's not public, so sharing is not possible. But I could offer a screen sharing.

[iluuu1994]

It's going to be very challenging to help you if we don't have a reliable reproducer. There's also a patch for master that should be merged soon which changes the order in which traits are bound, to hopefully make some trait edge cases less surprising. #15878 Possibly, this will help.