%Warning-WIDTHEXPAND: t/t_func_bad_width.v:13:13: Operator FUNCREF 'MUX' expects 40 bits on the Function Argument, but Function Argument's VARREF 'in' generates 39 bits.
                                                : ... In instance t
   13 |       out = MUX (in);
      |             ^~~
                      ... For warning description see https://verilator.org/warn/WIDTHEXPAND?v=latest
                      ... Use "/* verilator lint_off WIDTHEXPAND */" and lint_on around source to disable this message.
%Warning-WIDTHTRUNC: t/t_func_bad_width.v:13:11: Operator ASSIGN expects 4 bits on the Assign RHS, but Assign RHS's FUNCREF 'MUX' generates 32 bits.
                                               : ... In instance t
   13 |       out = MUX (in);
      |           ^
%Error: Exiting due to