A contravariant variation of #7585 that doesn't allow a violation.

ClassnameContravariantWrapperViolation.php

<?hh // strict
<<__ConsistentConstruct>>
abstract class ConWrapper<-T> {
	public function __construct() {}
	abstract public function act(T $v): void;
}
class ConcreteWrapper extends ConWrapper<OtherBase> {
	public function act(OtherBase $v): void {
		$v->fn();
	}
}
class Base {}
class OtherBase {
	public function fn(): void {}
}
function violate(classname<ConWrapper<OtherBase>> $C): void {
	(new $C())->act(new Base()); // Invalid argument (Typing[4110]) 
}
// attempted violation: violate(ConcreteWrapper::class)