https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109935
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
C{B{1}};
Does work though.
I suspect the issue is cannot figure out that {1} can be bound to B<T> and
deudce T there and even GCC gives that as a reason:
<source>:7:8: note: candidate: 'template<class T> C(B<T>)-> C<T>'
7 | struct C : public B<T> {
| ^
<source>:7:8: note: template argument deduction/substitution failed:
<source>:15:10: note: couldn't deduce template parameter 'T'
15 | C{{1}};
| ^
