C++
gcc HEAD 11.0.0 20210203 (experimental)
$ g++ prog.cc -std=c++20
prog.cc: In instantiation of 'failcase()::<lambda(auto:1&&)> [with auto:1 = int]': prog.cc:20:9: required from here prog.cc:17:9: error: 'co_return' cannot be used in a 'constexpr' function 17 | co_return; | ^~~~~~~~~