Hint to everybody else, try this PR with a different language for xmas and new year, and be sure to report your results :)
Good hint - so I tried C/C++ to have it simple ;-). Here's the result:
https://github.com/techee/geany/tree/cxx_parser
There are definitely some things that could be improved about it (e.g. anonymous names), but parsing itself is about as good as the upstream ctags parser ability.
@elextr Since you like finding all the possible cases where the current C parser fails, would you give it a try?