?? Yield: It is a compile-time error if a yield statement appears in a function that is not a generator function.
static const CompileTimeErrorCode YIELD_IN_NON_GENERATOR = CompileTimeErrorCode( 'YIELD_IN_NON_GENERATOR', "Yield statements must be in a generator function " "(one marked with either 'async*' or 'sync*').", correction: "Try adding 'async*' or 'sync*' to the enclosing function.")