Zend: Make Closure covariant to callable

Author: Girgias

Zend/tests/type_declarations/callable/callable_variance_closure.phpt

@@ -10,5 +10,6 @@ class B extends A {
     public function foo(callable $c): Closure {}
 }
 ?>
---EXPECTF--
-Fatal error: Declaration of B::foo(callable $c): Closure must be compatible with A::foo(Closure $c): callable in %s on line %d
+OK
+--EXPECT--
+OK

Zend/zend_inheritance.c

@@ -23,6 +23,7 @@
 #include "zend_execute.h"
 #include "zend_inheritance.h"
 #include "zend_interfaces.h"
+#include "zend_closures.h"
 #include "zend_smart_str.h"
 #include "zend_operators.h"
 #include "zend_exceptions.h"
@@ -478,6 +479,19 @@ static inheritance_status zend_is_class_subtype_of_type(
 		}
 	}
 
+	/* If the parent has 'callable' as a return type, then Closure satisfies the co-variant check */
+	if (ZEND_TYPE_FULL_MASK(proto_type) & MAY_BE_CALLABLE) {
+		if (!fe_ce) fe_ce = lookup_class(fe_scope, fe_class_name);
+		if (!fe_ce) {
+			have_unresolved = 1;
+		} else if (fe_ce == zend_ce_closure) {
+			track_class_dependency(fe_ce, fe_class_name);
+			return INHERITANCE_SUCCESS;
+		} else {
+			return INHERITANCE_ERROR;
+		}
+	}
+
 	zend_type *single_type;
 
 	/* Traverse the list of parent types and check if the current child (FE)