Feature: ChainToParameterlessConstructor

[Tim-Maes]

fixes #253

When using [Facet] with GenerateParameterlessConstructor = false, users who have custom initialization logic in their parameterless constructor had no way to ensure that logic runs when using ToFacet<>() or constructing from a source.

public class ModelType
{
    public int MaxValue { get; set; }
}

[Facet(typeof(ModelType), GenerateParameterlessConstructor = false)]
public partial class MyType
{
    public int Value { get; set; }

    public MyType()
    {
        // This initialization logic was NOT being called when mapping
        Value = 100;
    }
}

Feature

Added a new ChainToParameterlessConstructor property to the [Facet] attribute. When set to true, the generated constructor that takes the source type will chain to the parameterless constructor using : this().

Usage

public class ModelType
{
    public int MaxValue { get; set; }
}

[Facet(typeof(ModelType), GenerateParameterlessConstructor = false, ChainToParameterlessConstructor = true)]
public partial class MyType
{
    public int Value { get; set; }
    public bool Initialized { get; set; }

    public MyType()
    {
        // This initialization logic WILL now run when mapping
        Value = 100;
        Initialized = true;
    }
}

// Usage
var source = new ModelType { MaxValue = 42 };
var dto = new MyType(source);

// dto.Value == 100 (from parameterless constructor)
// dto.Initialized == true (from parameterless constructor)
// dto.MaxValue == 42 (from source mapping)

Generated Code

With ChainToParameterlessConstructor = true:

public partial class MyType
{
    public int MaxValue { get; set; }

    public MyType(ModelType source) : this()  // <-- Chains to parameterless ctor
    {
        this.MaxValue = source.MaxValue;
    }
}

Without chaining (default behavior):

public partial class MyType
{
    public int MaxValue { get; set; }

    public MyType(ModelType source)  // <-- No chaining
    {
        this.MaxValue = source.MaxValue;
    }
}

Notes

• This feature works with both the main constructor and the depth-aware constructor
• Default value is false to maintain backward compatibility
• Can be combined with other attributes like Configuration, BeforeMapConfiguration, etc.