How to pass multiple flags as a Cake argument?

Question

We have a number of build flags we'd like to be able to pass to our Cake script as a single argument. Based on this answer and the TypeConverter documentation, I would expect the following simplified code to compile and run.

public class BuildFlagsConverter : TypeConverter
{
  public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
  {
    return true;
  }

  public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
  {
    return BuildFlags.None;
  }
}

[Flags]
[TypeConverter(typeof(BuildFlagsConverter))]
enum BuildFlags
{
  None = 0,
  FeatureOne = 1,
  FeatureTwo = 2,
  All = FeatureOne | FeatureTwo,
}

var buildFlags = Argument<BuildFlags>("buildFlags", BuildFlags.All);

I would then expect to be able to call cake --buildFlags="FeatureOne|FeatureTwo" to build. Instead, Cake is throwing the following error:

Error: One or more errors occurred. (FeatureOne|FeatureTwo is not a valid value for BuildFlags.)

I thought this might be related to using an enum instead of a class, so I tried converting BuildFlags to a static class with static getters for each of the above values. However, in this case I was still getting an error:

Error: One or more errors occurred. (TypeConverter cannot convert from System.String.)

Am I missing something? Is there a better way to do this? Ideally, we would still get the enum syntax within the script itself, but I suppose I'm open to alternatives.

Answer 1

Update

After troubleshooting, it seems that using custom type converters works well on .NET, .NET Core, and .NET Framework, but does not work well on Mono.

Reported as a bug - https://github.com/cake-build/cake/issues/3333

---

Is it possible that you're using an old version of Cake that doesn't support custom type converters?

I tested your code on the latest version of Cake as of this writing (1.1.0) and it worked as expected.

---

using System.ComponentModel;
using System.Globalization;

public class BuildFlagsConverter : TypeConverter
{
    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
    {
        return true;
    }

    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
    {
        return BuildFlags.None;
    }
}

[Flags]
[TypeConverter(typeof(BuildFlagsConverter))]
enum BuildFlags
{
    None = 0,
    FeatureOne = 1,
    FeatureTwo = 2,
    All = FeatureOne | FeatureTwo,
}

var buildFlags = Argument<BuildFlags>("buildFlags", BuildFlags.All);
Information("buildFlags converted to: {0}", buildFlags);