static return type loses information about intersection types

[MatmaRex]

static return type loses information about intersection types.

Example: https://phan.github.io/demo/?code=%3C%3Fphp%0A%0Aclass+Foo+{%0A%09function+a()%3A+static+{%0A%09%09return+%24this%3B%0A%09}%0A}%0A%0Ainterface+Woop+{%0A%09function+b()%3A+static%3B%0A}%0A%0Aclass+Bar+extends+Foo+implements+Woop+{%0A%09function+b()%3A+static+{%0A%09%09return+%24this%3B%0A%09}%0A}%0A%0Afunction+newBar()%3A+Foo%26Woop+{%0A%09return+new+Bar%3B%0A}%0A%0A(new+Bar)->a()->b()%3B%0AnewBar()->a()->b()%3B%0A

<?php

class Foo {
	function a(): static {
		return $this;
	}
}

interface Woop {
	function b(): static;
}

class Bar extends Foo implements Woop {
	function b(): static {
		return $this;
	}
}

function newBar(): Foo&Woop {
	return new Bar;
}

(new Bar)->a()->b();
newBar()->a()->b();

Outputs:

input:24: PhanUndeclaredMethod Call to undeclared method \Foo::b (Did you mean expr->a())

(Phan 5.4.1)

It seems to me that, if newBar()'s type is Foo&Woop, and Foo::a returns static, then newBar()->a()'s type should also be Foo&Woop – however, it is apparently Foo.

(The same thing happens when the method is documented with @return static, or @return $this, instead of the static PHP type.)

I've tested the same example using Psalm and PHPStan, and they both accept this code:

• https://psalm.dev/r/bf1d0f54e2
• https://phpstan.org/r/e652b93f-575e-4210-b09d-42728f36ed3d