Fixed covariance of return-by-ref constraints

NEWS

@@ -50,6 +50,7 @@
   large amount of data) (CVE-2010-3710). (Adam)
 - Fixed ReflectionProperty::isDefault() giving a wrong result for properties
   obtained with ReflectionClass::getProperties(). (Gustavo)
+- Fixed covariance of return-by-ref constraints. (Etienne)
 
 - Fixed bug #53198 (changing INI setting "from" with ini_set did not have any
   effect). (Gustavo)

Zend/tests/objects_032.phpt

@@ -0,0 +1,40 @@
+--TEST--
+Covariant return-by-ref constraints
+--FILE--
+<?php
+
+class A implements ArrayAccess {
+    public $foo = array();
+
+    public function &offsetGet($n) {
+        return $this->foo[$n];
+    }
+
+    public function offsetSet($n, $v) {
+    }
+    public function offsetUnset($n) {
+    }
+    public function offsetExists($n) {
+    }
+}
+
+$a = new A;
+
+$a['foo']['bar'] = 2;
+
+var_dump($a);
+
+?>
+==DONE==
+--EXPECTF--
+object(A)#1 (1) {
+  ["foo"]=>
+  array(1) {
+    ["foo"]=>
+    array(1) {
+      ["bar"]=>
+      int(2)
+    }
+  }
+}
+==DONE==

Zend/zend_compile.c

@@ -2557,7 +2557,8 @@ static zend_bool zend_do_perform_implementation_check(const zend_function *fe, c
 		return 0;
 	}
 
-	if (fe->common.return_reference != proto->common.return_reference) {
+	/* by-ref constraints on return values are covariant */
+	if (proto->common.return_reference && !fe->common.return_reference) {
 		return 0;
 	}
 
@@ -2581,6 +2582,8 @@ static zend_bool zend_do_perform_implementation_check(const zend_function *fe, c
 			/* Only one has an array type hint and the other one doesn't */
 			return 0;
 		}
+
+		/* by-ref constraints on arguments are invariant */
 		if (fe->common.arg_info[i].pass_by_reference != proto->common.arg_info[i].pass_by_reference) {
 			return 0;
 		}