%Error-IMPURE: t/t_interface_func_impure_bad.v:21:8: Unsupported: External variable referenced by non-inlined function/task: 'external_write'
                                                   : ... note: In instance 't.i'
   21 |   task external_write;
      |        ^~~~~~~~~~~~~~
               t/t_interface_func_impure_bad.v:23:5: ... Location of the external reference: 'external_sig'
   23 |     external_sig = 1'b1;
      |     ^~~~~~~~~~~~
               ... For error description see https://verilator.org/warn/IMPURE?v=latest
%Error: Exiting due to