Stop the recursion when an enum case value reads itself

[SanderMuller]

A backed enum case can read its own value, for example case A = self::A->value;. ClassReflection::getEnumCase() then resolved the same value expression again and again. With the Turbo extension, the worker stopped on the call stack limit. Without it, the worker ran until the memory limit stopped it.

getEnumCase() and getEnumCases() now resolve the case value through the new InitializerExprTypeResolver::getEnumCaseValueType(). This method uses the currentlyResolvingClassConstant guard that class constants already use, with the key Class::case. The read of a case that is being resolved now gives mixed, as the read of a class constant that is being resolved does. So case A = self::A->value; resolves to mixed, and case A = self::A->value . 'x'; resolves to non-falsy-string, the same as const A = self::A . 'x';.

When the value resolves to mixed, EnumSanityRule reports the case with enum.caseType:

Enum case E::A value mixed does not match the "string" type.

PHP rejects this code at runtime with "Cannot declare self-referencing constant", so the error is on code that cannot run.

The Turbo extension mirrors the change in InitializerExprTypeResolver.cpp and ClassReflection.cpp.

The tests cover these cases:

• a string and an int backed case that read themselves
• two cases that read each other, through getEnumCase() and through getEnumCases()
• a cycle across two enums
• a concatenation
• a valid forward reference

Closes phpstan/phpstan#15458

🤖 Generated with Claude Code

[staabm]

Suggested change

	* Resolves the backing value of an enum case. A read of the case while
	* its value is being resolved gives mixed, like a class constant does.
	* Resolves the backing value of an enum case. A read of the case while
	* its value is being resolved gives mixed - like a class constant does - to prevent endless recursions.

[staabm]

needs rebase

[staabm]

thank you!