Custom C++11 attributes in plugins/tools

Over the years I’ve seen several posts saying “we need to allow plugins/tools to be able to add custom C++11 attributes to the AST without needing to modify the in-tree”

IIRC, someone even had patches for this years ago, but I don’t think they were ever merged. At least one other person (I think Sean Hunt?) was going to do the necessary work years ago. As far as I can tell, there is still no machinery for doing it. Is that still accurate? I am writing a few plugins now and would really like this.

Correct, there currently is not machinery for doing this, but there's
definitely a desire (it's been on my attribute TODO list for a while).