gcc/testsuite/g++.dg/coroutines/co-yield-syntax-03-auto.C

//  { dg-additional-options "-fsyntax-only -w" }

#include "coro.h"

auto bar () {
  co_yield 5;  // { dg-error "cannot be used in a function with a deduced return type" }
}

int main () {
  bar ();
  return 0;
}