https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121068
--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> --- The intent of the patch was to support new (&union_.member) T syntax like union_.member = T() for setting the active member, as in https://eel.is/c++draft/class.union#general-example-3 but adding the library fluff obscures that syntax, and so is less clear that it ought to work.
