From 7fbfcfa8515341ffdafd934fe6a014fd50bdf269 Mon Sep 17 00:00:00 2001
From: Nikita Popov <nikita.ppv@gmail.com>
Date: Mon, 10 May 2021 09:45:48 +0200
Subject: [PATCH] Don't autoload classes during covariant type check against
 mixed

mixed should be behaving the same way as no type here, and not
require X to be autoloaded. Everything apart from "void" is trivially
covariant to "mixed".
---
 .../variance/mixed_return_type.phpt           | 20 +++++++++++++++++++
 Zend/zend_inheritance.c                       |  7 +++++++
 2 files changed, 27 insertions(+)
 create mode 100644 Zend/tests/type_declarations/variance/mixed_return_type.phpt

diff --git a/Zend/tests/type_declarations/variance/mixed_return_type.phpt b/Zend/tests/type_declarations/variance/mixed_return_type.phpt
new file mode 100644
index 00000000000..45b2440b972
--- /dev/null
+++ b/Zend/tests/type_declarations/variance/mixed_return_type.phpt
@@ -0,0 +1,20 @@
+--TEST--
+Everything is trivially a subtype of mixed
+--FILE--
+<?php
+
+spl_autoload_register(function($class) {
+    echo "Loading $class\n";
+});
+
+class A {
+    public function test(): mixed {}
+}
+class B extends A {
+    public function test(): X {}
+}
+
+?>
+===DONE===
+--EXPECT--
+===DONE===
diff --git a/Zend/zend_inheritance.c b/Zend/zend_inheritance.c
index 4b161692af7..b00c5e5c60b 100644
--- a/Zend/zend_inheritance.c
+++ b/Zend/zend_inheritance.c
@@ -429,6 +429,13 @@ static inheritance_status zend_perform_covariant_type_check(
 {
 	ZEND_ASSERT(ZEND_TYPE_IS_SET(fe_type) && ZEND_TYPE_IS_SET(proto_type));
 
+	/* Apart from void, everything is trivially covariant to the mixed type.
+	 * Handle this case separately to ensure it never requires class loading. */
+	if (ZEND_TYPE_PURE_MASK(proto_type) == MAY_BE_ANY &&
+			!ZEND_TYPE_CONTAINS_CODE(fe_type, IS_VOID)) {
+		return INHERITANCE_SUCCESS;
+	}
+
 	/* Builtin types may be removed, but not added */
 	uint32_t fe_type_mask = ZEND_TYPE_PURE_MASK(fe_type);
 	uint32_t proto_type_mask = ZEND_TYPE_PURE_MASK(proto_type);