Warn if return type on internal __toString() is missing

Author: nikic

Zend/zend_API.c

@@ -2716,6 +2716,8 @@ ZEND_API zend_result zend_register_functions(zend_class_entry *scope, const zend
 		 * interface. */
 		if (scope && zend_string_equals_literal_ci(internal_function->function_name, "__tostring") &&
 				!(internal_function->fn_flags & ZEND_ACC_HAS_RETURN_TYPE)) {
+			zend_error(E_CORE_WARNING, "%s::__toString() implemented without string return type",
+				ZSTR_VAL(scope->name));
 			internal_function->arg_info = (zend_internal_arg_info *) arg_info_toString + 1;
 			internal_function->fn_flags |= ZEND_ACC_HAS_RETURN_TYPE;
 			internal_function->num_args = internal_function->required_num_args = 0;

ext/zend_test/test.stub.php

@@ -21,11 +21,8 @@ class _ZendTestClass implements _ZendTestInterface {
 
         public static function is_object(): int {}
 
-        /**
-         * @deprecated
-         * @return string
-         */
-        public function __toString() {}
+        /** @deprecated */
+        public function __toString(): string {}
 
         public function returnsStatic(): static {}
 

ext/zend_test/test_arginfo.h

@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: d0ffefd20355db472f4a8adc018bec959e670bb3 */
+ * Stub hash: 7326163f8ce5340c12e74af72d47a8926eb39786 */
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_zend_test_array_return, 0, 0, IS_ARRAY, 0)
 ZEND_END_ARG_INFO()
@@ -77,7 +77,7 @@ ZEND_END_ARG_INFO()
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_class__ZendTestClass_is_object, 0, 0, IS_LONG, 0)
 ZEND_END_ARG_INFO()
 
-ZEND_BEGIN_ARG_INFO_EX(arginfo_class__ZendTestClass___toString, 0, 0, 0)
+ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_class__ZendTestClass___toString, 0, 0, IS_STRING, 0)
 ZEND_END_ARG_INFO()
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_class__ZendTestClass_returnsStatic, 0, 0, IS_STATIC, 0)