[MVVM] Don't add default parameter in attribute constructor

[hellow554]

Describe the bug

I have an Attribute, which constructor looks like this:

[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false, Inherited = false)]
public class CrossValidateAttribute : ValidationAttribute {
    public CrossValidateAttribute([CallerMemberName] string? member = null) { }
}

The idea is to get the properties name when this gets constructed. If I put this on a normal Property, e.g.

[CrossValidate]
public string Foo { ... }

it will work and I get Foo as content of member.

But, if I put this on an [ObservableProperty] the generator will output this:

[ObservableProperty]
[CrossValidate]
private string? bar;

/// <inheritdoc cref="bar"/>
[global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator", "8.2.0.0")]
[global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
[global::XXX.CrossValidateAttribute(null)]
public string? Bar { ... }

Here you can see the XXX.CrossValidateAttribute(null) call, which is not want I want.

Can this be done the way I want it, e.g. XXX.CrossValidateAttribute()?

IDE and version

VS 2022

IDE version

Version 17.7.6

Nuget packages

• [ ] CommunityToolkit.Common
• [ ] CommunityToolkit.Diagnostics
• [ ] CommunityToolkit.HighPerformance
• [X] CommunityToolkit.Mvvm (aka MVVM Toolkit)

Nuget package version(s)

8.2.2

Additional context

No response

Help us help you

Yes, I'd like to be assigned to work on this item

[JochenMader]

Hi there

I did some research on this one and found following:

In ../src/CommunityToolkit.Mvvm.SourceGenerators/ComponentModel/Models/AttributeInfo.cs:41

        // Get the constructor arguments
        foreach (TypedConstant typedConstant in attributeData.ConstructorArguments)
        {
            constructorArguments.Add(TypedConstantInfo.Create(typedConstant));
        }

For testing purposed I replaced this part with:

        // Get the constructor arguments
        for (int i = 0; i < attributeData.AttributeConstructor.Parameters.Count(); i++)
        {
            if (attributeData.AttributeConstructor.Parameters[i].HasExplicitDefaultValue) break;

            var typedConstant = attributeData.ConstructorArguments[i];
            var info = TypedConstantInfo.Create(typedConstant);
            constructorArguments.Add(info);
        }

Parameters with default value are skipped.

Maybe this (or somehow better) can be discussed as a solution.

best regards