code: public void strictWarning(DiagnosticPosition pos, String key, Object ... args) {
          writeDiagnostic(diags.warning(null, source, pos, key, args));
          nwarnings++;
      }
docs: Report a warning that cannot be suppressed.
  @param pos    The source position at which to report the warning.
  @param key    The key for the localized warning message.
  @param args   Fields of the warning message.