[Bug c++/84075] Template parameter not resolved: invalid application of ‘sizeof’ to incomplete type ‘boost::serialization::U’

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84075

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #2)
> Here's the result of many hours of creduction 

(and some manual reduction)