When you try to load an abstract class with annotations, the following code throws an exception;

$class = new \ReflectionClass($class);
if ($class->isAbstract()) {
    throw new \InvalidArgumentException(sprintf('Annotations from class "%s" cannot be read as it is abstract.', $class));
}

But the $class variable is now a ReflectionClass instance and the complete class file contents are shown in the exception.