Infinite recursion on a backed enum case whose value reads its own value #15458

Bug report

PHPStan does not finish on this file:

<?php

enum E: string
{
	case A = self::A->value;
}

With the Turbo extension (2.3.1 installed through Composer), the run stops after about 2 seconds with an internal error:

Internal error: Maximum call stack size of 8339456 bytes (zend.max_allowed_stack_size - zend.reserved_stack_size) reached. Infinite recursion? while analysing file

Without the Turbo extension, the recursion continues until the worker reaches the PHP memory limit. With memory_limit=1G, the 2.3.x branch stops after 4 seconds with "PHPStan process crashed because it reached configured PHP memory limit: 1G". With memory_limit=-1, I stopped the 2.0.0, 2.1.30, 2.2.17 and 2.3.1 phars after 40 seconds. After 8 seconds, a --debug run of 2.3.x had a call stack of about 2 million frames. An int backed enum and two cases that read each other (case A = self::B->value; case B = self::A->value;) behave the same.

The stack repeats these four frames:

InitializerExprTypeResolver::getType()          (PropertyFetch, InitializerExprTypeResolver.php:511)
ObjectType::getInstanceProperty()
EnumCaseObjectType::getUnresolvedInstancePropertyPrototype()
ClassReflection::getEnumCase()                  (resolves the value expression again, ClassReflection.php:1083)

EnumSanityRule starts it. For a class constant, InitializerExprTypeResolver has the currentlyResolvingClassConstant guard, so const A = self::A; returns mixed. The enum case path has no such guard.

PHP rejects the code at runtime with Cannot declare self-referencing constant self::A.

Code snippet that reproduces the problem

The snippet is at the top of this report. I could not create a playground link: https://api.phpstan.org/analyse returns Internal server error for this code. The same request with case A = 'a'; returns a normal result.

Expected output

The analysis finishes, as it does for const A = self::A;. PHPStan could also report the self-reference, but it does not do that for the class constant either.