anchor.diff:        passThrough(argument);
         return;
       }
  -    helpAndFail("Error: Unsupported dump-info format '$argument', "
  +    helpAndFail("Unsupported dump-info format '$argument', "
           "supported formats are: json or binary");
     }
   
     String nullSafetyMode = null;
     void setNullSafetyMode(String argument) {
       if (nullSafetyMode != null && nullSafetyMode != argument) {
  -      helpAndFail("Error: cannot specify both $nullSafetyMode and $argument.");
  +      helpAndFail("Cannot specify both $nullSafetyMode and $argument.");
       }
       nullSafetyMode = argument;
       passThrough(argument);
  
positive.code: 
    void setOutput(Iterator<String> arguments) {
      outputSpecified = true;
      String path;
      if (arguments.current == '-o') {
        if (!arguments.moveNext()) {
          helpAndFail('Error: Missing file after -o option.');
        }
        path = arguments.current;
      } else {
        path = extractParameter(arguments.current);
      }
      out = Uri.base.resolve(fe.nativeToUriPath(path));
    }
  
negative.code:     OptionHandler('${Flags.codegenShards}=.+', setCodegenShards),
      OptionHandler(Flags.cfeOnly, setCfeOnly),
      OptionHandler(Flags.debugGlobalInference, passThrough),
      OptionHandler('--output(?:=.+)?|--out(?:=.+)?|-o.*', setOutput,
          multipleArguments: true),
      OptionHandler('-O.*', setOptimizationLevel),
      OptionHandler(Flags.allowMockCompilation, ignoreOption),
      OptionHandler(Flags.fastStartup, ignoreOption),
  