public void error(DiagnosticPosition pos, Error errorKey) {
        report(diags.error(null, source, pos, errorKey));
    }
public void error ( DiagnosticPosition pos , Error errorKey ) { report ( diags . error ( null , source , pos , errorKey ) ) ; }
Report an error, unless another error was already reported at same
source position.
@param pos    The source position at which to report the error.
@param errorKey    The key for the localized error message.