@0rzech its actually a file glob, not a regex, and I would expect the time is more likely spent in compiling the pattern, not matching it, since its normal use is against directories full of files not one at a time like this use. Sure its exaggerated to worry about one, ten, 100 but where to stop? And as I said picking favourites is probably not something Geany should do.
Its a glob, not `ends_with`, because some patterns are not actually extensions, eg `makefile.*`