gcc/testsuite/g++.dg/expr/lval4.C

// ++i is always an lvalue
void
f()
{
  bool i = 0;
  ++i = 3;
  // { dg-warning "deprecated" "" { target { ! c++17 } } .-1 }
  // { dg-error "forbidden" "" { target c++17 } .-2 }
}