3.6.0 - unflattening configuration doesn't seem to work

[IanKemp]

I have some classes and interfaces:

interface IExternalRequest
{
    int? UserId { get; set; }
    string? UserName { get; set; }
}

record SomeExternalRequest(
    int Foo,
    bool Bar,
    int? UserId,
    string? UserName)
    : IExternalRequest;

I want to unflatten these into:

record InternalUser(
    int? Id,
    string? Name);

record SomeInternalRequest(
    int Foo,
    bool Bar,
    InternalUser User);

So I created a user-defined mapping for IExternalRequest => InternalUser:

internal static class IExternalRequestMapper
{
    public static InternalUser MapToUser(this IExternalRequest request)
        => new(
            request.UserId,
            request.UserName);
}

and then another for SomeExternalRequest => SomeInternalRequest:

[Mapper]
[UseStaticMapper(typeof(IExternalRequestMapper))]
internal static partial class SomeRequestMapper
{
    public static partial SomeInternalRequest Map(this SomeExternalRequest request);
}

Unfortunately this doesn't work - Mapperly complains that "SomeInternalRequest has no accessible constructor with mappable arguments", as well as that UserId and UserName are not mapped from the source and User is not found on the source.

I then tried adding MapPropertyFromSourceAttribute:

[Mapper]
[UseStaticMapper(typeof(IExternalRequestMapper))]
internal static partial class SomeRequestMapper
{
    [MapPropertyFromSource(nameof(SomeInternalRequest.User), Use = nameof(IExternalRequestMapper.MapToUser))]
    public static partial SomeInternalRequest Map(this SomeExternalRequest request);
}

but that complains that "The referenced mapping named MapToUser was not found".

Am I doing something wrong, or is this not a supported scenario by Mapperly?

[latonz]

The usage of external mappers in MapPropertyFromSourceAttribute.Use is currently not supported, see #1298