https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87709
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Oops, I missed the first line of the diagnostic. The error from trunk is:
ctad.cc:11:12: error: missing template arguments after 'lit'
11 | auto r2 = (lit(0)) + lit(0);
| ^~~
ctad.cc:2:8: note: 'template<class T> struct lit' declared here
2 | struct lit {
| ^~~
