Fix GH-9655: Allow pure intersection types to be implicitly nullable

Closes GH-9659

Author: HypeMC

NEWS

@@ -2,6 +2,10 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.2.0RC4
 
+- Core:
+  . Fixed bug GH-9655 (Pure intersection types cannot be implicitly nullable)
+    (Girgias)
+
 - Streams:
   . Fixed bug GH-9590 (stream_select does not abort upon exception or empty
     valid fd set). (Arnaud)

Zend/tests/type_declarations/intersection_types/implicit_nullable_intersection_type.phpt

@@ -1,10 +1,14 @@
 --TEST--
-Intersection types cannot be implicitly nullable
+Intersection types can be implicitly nullable
 --FILE--
 <?php
 
-function foo(X&Y $foo = null) {}
+function foo(X&Y $foo = null) {
+    var_dump($foo);
+}
+
+foo(null);
 
 ?>
 --EXPECTF--
-Fatal error: Cannot use null as default value for parameter $foo of type X&Y in %s on line %d
+NULL

Zend/zend_compile.c

@@ -6819,15 +6819,6 @@ static void zend_compile_params(zend_ast *ast, zend_ast *return_type_ast, uint32
 				zend_error_noreturn(E_COMPILE_ERROR, "never cannot be used as a parameter type");
 			}
 
-			if (force_nullable && ZEND_TYPE_IS_INTERSECTION(arg_info->type)) {
-				/* We drop the nullable type flag to generate the correct type string */
-				ZEND_TYPE_FULL_MASK(arg_info->type) = ZEND_TYPE_FULL_MASK(arg_info->type) & ~MAY_BE_NULL;
-				zend_string *type_str = zend_type_to_string(arg_info->type);
-				zend_error_noreturn(E_COMPILE_ERROR,
-					"Cannot use null as default value for parameter $%s of type %s",
-					ZSTR_VAL(name), ZSTR_VAL(type_str));
-			}
-
 			if (default_type != IS_UNDEF && default_type != IS_CONSTANT_AST && !force_nullable
 					&& !zend_is_valid_default_value(arg_info->type, &default_node.u.constant)) {
 				zend_string *type_str = zend_type_to_string(arg_info->type);