I guess this is somewhat by design that no autocomplete results except snippets are shown inside a declaration because you obviously want to declare something new.

But for the same reason that snippets are shown (I guess because the snippet could hold something like a default function you may want to use) it would make sense to also show macros. In my case i have some #define-s for a collection of function and variable attributes like these for interrupt routines:

and it would be great if those would also show up.
I also sometimes have #define-aliased the names of interrupt routines and hardware registers so I can easily swap them out later without digging through the code.
I would really like if there was at least an option to also show macros.