Avoid a E_DEPRECATED in _checkTypehint on PHP8

PHP8's reflection API changed to make room for handling of union-types. As one of the consequences `ReflectionParameter::getClass` got marked as deprecated.
This commit moves the legacy path behind a version-check for PHP versions before 8 and adds a new more complex path for PHP8+.

Author: bzikarsky

src/functions.php

@@ -343,9 +343,47 @@ function _checkTypehint(callable $callback, $object)
 
     $expectedException = $parameters[0];
 
-    if (!$expectedException->getClass()) {
+    // PHP before v8 used an easy API:
+    if (PHP_VERSION_ID < 80000) {
+        if (!$expectedException->getClass()) {
+            return true;
+        }
+
+        return $expectedException->getClass()->isInstance($object);
+    }
+
+    // Extract the type of the argument and handle different possibilities
+    $type = $expectedException->getType();
+    $types = [];
+
+    switch (true) {
+        case $type === null:
+            break;
+        case $type instanceof \ReflectionNamedType:
+            $types = [$type];
+            break;
+        case $type instanceof \ReflectionUnionType;
+            $types = $type->getTypes();
+            break;
+        default:
+            throw new \LogicException('Unexpected return value of ReflectionParameter::getType');
+    }
+
+    // If there is no type restriction, it matches
+    if (empty($types)) {
         return true;
     }
 
-    return $expectedException->getClass()->isInstance($object);
+    // Search for one matching named-type for success, otherwise return false
+    // A named-type can be either a class-name or a built-in type like string, int, array, etc.
+    foreach ($types as $type) {
+        $matches = ($type->isBuiltin() && \gettype($object) === $type->getName())
+            || (new \ReflectionClass($type->getName()))->isInstance($object);
+
+        if ($matches) {
+            return true;
+        }
+    }
+
+    return false;
 }