Attributes are not rendered when showing the source code

The question we need to first to answer is: what is the desired outcome here? I think the attribute class itself already has an api page because it is a class, after all. Everything marked with that attribute should have a reference to this page and vice versa much like it happens with annotations. I imagine there would be an object-type of attribute, and an attributes reference type for buildReferencesSection / findReferences. This is a fairly trivial affair, ✨ Support for OO hooks implementations in classes Postponed shows how to parse attributes.

A much more difficult question would be: what happens to the arguments of the attribute? The issue linked above definitely needs it -- perhaps it should special case for now and this issue should just store attributes as separate docblock entries and punt on argument processing. A followup would probably parse the arguments, use https://github.com/nikic/PHP-Parser/blob/master/doc/component/Constant_expression_evaluation.markdown and reference any classes and constants used here.