Parser fails when an empty value is given

[FreeApophis]

Example code

    static class Program
    {
        static void Main(string[] args)
        {
            var configuration = new Configuration();
            var parseResult = Parser.Default.ParseArguments<Configuration>(args).WithParsed(result => configuration = result);

            System.Console.WriteLine(parseResult.Tag);
            System.Console.WriteLine(configuration.Description);
        }
    }

    internal class Configuration
    {
        [Option('d', "description", HelpText = "Set the description from the project")]
        public string Description { get; set; }
    }

Running the Program with progam.exe --description="" results in a Parse Error:

ERROR(S):
  Token '--description=' is not recognized

This is probably the same issue as #358 - but the example syntaxt was different (--description without an equal sign), which is not what I expect. But I expect an empty string to be a valid value.

[lobster2012-user]

Hi, @FreeApophis
1.

public class Options_412
    {
        [Option('d', "description", HelpText = "Set the description from the project")]
        public string Description { get; set; }
    }

class Program
    {
        public static void Main(String[] args)
        {
            Console.WriteLine(string.Join(",", args.Select(z => $"({z})")));
            var configuration = new Options_412();
            var parseResult = Parser.Default.ParseArguments<Options_412>(args).WithParsed(result => configuration = result);

            System.Console.WriteLine(parseResult.Tag);
            System.Console.WriteLine(configuration.Description);
        }
    }

cmd>commandline_tests.console.exe  --description ""
(--description),()
Parsed

--description=
--description=""
--description=" "

Tokenizer.cs

 var tokenMatch = Regex.Match(text, "^([^=]+)=([^ ].*)$");

-->

 var tokenMatch = Regex.Match(text, "^([^=]+)=(.*)$");

This will fix the problem, but possibly breaking changes.

Should_return_error_if_option_format_with_equals_is_not_correct()
{
var args = new[] { "--option1 = fail", "--option2= fail" };

            var result = Tokenizer.Tokenize(args, name => NameLookupResult.OtherOptionFound, token => token);

            var tokens = result.SuccessfulMessages();

            Assert.NotNull(tokens);
            Assert.Equal(2, tokens.Count());
            Assert.Equal(ErrorType.BadFormatTokenError, tokens.First().Tag);
            Assert.Equal(ErrorType.BadFormatTokenError, tokens.Last().Tag);
}

3. Compromise
   var tokenMatch = Regex.Match(text, "^([^=]+)=(([^ ].*)|[\\s]*)$");
   Assept '\s*' or [^]...

[rmunn]

This will be fixed by #684 (which should be merged in before the upcoming 2.9 release). Once that PR is merged in, there will be a new parser setting called GetoptMode that adheres more strictly to the rules of GNU getopt, including allowing empty string values after an = sign. (So --description="" or even just --description= would work).