php8-attributes-non-attribute-class.php

<?php
namespace Acme;

@@Attribute
final class Attr1 {}

@@Attr1
final class Foo {}

$reflectionClass = new \ReflectionClass(Foo::class);
$attributes = $reflectionClass->getAttributes();

var_dump($attributes[0]->newInstance());

/*
Fatal error: Uncaught Error: Attempting to use non-attribute class "Acme\Attr1" as attribute in /app/attr.php:13
Stack trace:
#0 /app/attr.php(13): ReflectionAttribute->newInstance()
#1 {main}
  thrown in /app/attr.php on line 13
*/

php8-attributes-not-found.php

<?php
namespace Acme;

@@Attribute
final class Attr1 {}

@@Attr10
final class Foo {}

$reflectionClass = new \ReflectionClass(Foo::class);
$attributes = $reflectionClass->getAttributes();

var_dump($attributes[0]->newInstance());

/*
Fatal error: Uncaught Error: Attribute class "Acme\Attr10" not found in /app/attr.php:13
Stack trace:
#0 /app/attr.php(13): ReflectionAttribute->newInstance()
#1 {main}
  thrown in /app/attr.php on line 13
*/