Proposal for GenerationDepthBehavior.

Here is a generation Depth limiter behavior proposal.

fixture.Behaviors.Add(new GenerationDepthBehavior(2));

Had to re-implement ComposeIfMultiple for test because it’s internal.

public class GenerationDepthBehavior : ISpecimenBuilderTransformation
{
    private const int DefaultGenerationDepth = 1;
    private readonly int generationDepth;

    public GenerationDepthBehavior() : this(DefaultGenerationDepth)
    {
    }

    public GenerationDepthBehavior(int generationDepth)
    {
        if (generationDepth < 1)
            throw new ArgumentOutOfRangeException(nameof(generationDepth), "Generation depth must be greater than 0.");

        this.generationDepth = generationDepth;
    }


    public ISpecimenBuilderNode Transform(ISpecimenBuilder builder)
    {
        if (builder == null) throw new ArgumentNullException(nameof(builder));

        return new GenerationDepthGuard(builder, new GenerationDepthHandler(), this.generationDepth);
    }
}

public interface IGenerationDepthHandler
{

    object HandleGenerationDepthLimitRequest(object request, IEnumerable<object> recordedRequests, int depth);
}

public class DepthSeededRequest : SeededRequest
{
    public int Depth { get; }
    public DepthSeededRequest(object request, object seed, int depth) : base(request, seed)
    {
        Depth = depth;
    }
}

public class GenerationDepthGuard : ISpecimenBuilderNode
{
    private readonly ThreadLocal<Stack<DepthSeededRequest>> requestsByThread
        = new ThreadLocal<Stack<DepthSeededRequest>>(() => new Stack<DepthSeededRequest>());

    private Stack<DepthSeededRequest> GetMonitoredRequestsForCurrentThread() => this.requestsByThread.Value;


    public GenerationDepthGuard(ISpecimenBuilder builder)
        : this(builder, EqualityComparer<object>.Default)
    {
    }

    public GenerationDepthGuard(
        ISpecimenBuilder builder,
        IGenerationDepthHandler depthHandler)
        : this(
            builder,
            depthHandler,
            EqualityComparer<object>.Default,
            1)
    {
    }

    public GenerationDepthGuard(
        ISpecimenBuilder builder,
        IGenerationDepthHandler depthHandler,
        int generationDepth)
        : this(
            builder,
            depthHandler,
            EqualityComparer<object>.Default,
            generationDepth)
    {
    }


    public GenerationDepthGuard(ISpecimenBuilder builder, IEqualityComparer comparer)
    {
        this.Builder = builder ?? throw new ArgumentNullException(nameof(builder));
        this.Comparer = comparer ?? throw new ArgumentNullException(nameof(comparer));
        this.GenerationDepth = 1;
    }


    public GenerationDepthGuard(
        ISpecimenBuilder builder,
        IGenerationDepthHandler depthHandler,
        IEqualityComparer comparer)
        : this(
        builder,
        depthHandler,
        comparer,
        1)
    {
    }

    public GenerationDepthGuard(
        ISpecimenBuilder builder,
        IGenerationDepthHandler depthHandler,
        IEqualityComparer comparer,
        int generationDepth)
    {
        if (builder == null) throw new ArgumentNullException(nameof(builder));
        if (depthHandler == null) throw new ArgumentNullException(nameof(depthHandler));
        if (comparer == null) throw new ArgumentNullException(nameof(comparer));
        if (generationDepth < 1)
            throw new ArgumentOutOfRangeException(nameof(generationDepth), "Generation depth must be greater than 0.");

        this.Builder = builder;
        this.GenerationDepthHandler = depthHandler;
        this.Comparer = comparer;
        this.GenerationDepth = generationDepth;
    }


    public ISpecimenBuilder Builder { get; }

    public IGenerationDepthHandler GenerationDepthHandler { get; }

    public int GenerationDepth { get; }

    public int CurrentDepth { get; }

    public IEqualityComparer Comparer { get; }

    protected IEnumerable RecordedRequests => this.GetMonitoredRequestsForCurrentThread();

    public virtual object HandleGenerationDepthLimitRequest(object request, int currentDepth)
    {
        return this.GenerationDepthHandler.HandleGenerationDepthLimitRequest(
            request,
            this.GetMonitoredRequestsForCurrentThread(), currentDepth);
    }

    public object Create(object request, ISpecimenContext context)
    {
        if (request is SeededRequest)
        {
            int currentDepth = -1;

            var requestsForCurrentThread = this.GetMonitoredRequestsForCurrentThread();
            
            if (requestsForCurrentThread.Count > 0)
            {
                currentDepth = requestsForCurrentThread.Max(x => x.Depth) + 1;
            }

            DepthSeededRequest depthRequest = new DepthSeededRequest(((SeededRequest)request).Request, ((SeededRequest)request).Seed, currentDepth);

            if (depthRequest.Depth >= this.GenerationDepth)
            {
                return HandleGenerationDepthLimitRequest(request, depthRequest.Depth);
            }

            requestsForCurrentThread.Push(depthRequest);
            try
            {
                return this.Builder.Create(request, context);
            }
            finally
            {
                requestsForCurrentThread.Pop();
            }
        }
        else
        {
            return this.Builder.Create(request, context);
        }
    }

    public virtual ISpecimenBuilderNode Compose(
        IEnumerable<ISpecimenBuilder> builders)
    {
        var composedBuilder = ComposeIfMultiple(
            builders);
        return new GenerationDepthGuard(
            composedBuilder,
            this.GenerationDepthHandler,
            this.Comparer,
            this.GenerationDepth);
    }

    internal static ISpecimenBuilder ComposeIfMultiple(IEnumerable<ISpecimenBuilder> builders)
    {
        ISpecimenBuilder singleItem = null;
        List<ISpecimenBuilder> multipleItems = null;
        bool hasItems = false;

        using (var enumerator = builders.GetEnumerator())
        {
            if (enumerator.MoveNext())
            {
                singleItem = enumerator.Current;
                hasItems = true;

                while (enumerator.MoveNext())
                {
                    if (multipleItems == null)
                    {
                        multipleItems = new List<ISpecimenBuilder> { singleItem };
                    }

                    multipleItems.Add(enumerator.Current);
                }
            }
        }

        if (!hasItems)
        {
            return new CompositeSpecimenBuilder();
        }

        if (multipleItems == null)
        {
            return singleItem;
        }

        return new CompositeSpecimenBuilder(multipleItems);
    }

    public virtual IEnumerator<ISpecimenBuilder> GetEnumerator()
    {
        yield return this.Builder;
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return this.GetEnumerator();
    }
}

public class GenerationDepthHandler : IGenerationDepthHandler
{
    public object HandleGenerationDepthLimitRequest(
        object request,
        IEnumerable<object> recordedRequests, int depth)
    {
        return new OmitSpecimen();
    }
}

[zvirja]

@malylemire1 Would you be fine if we postpone this for now and implement it later only if we see a lot of requests for this feature?

I’m sorry we cannot include every desired feature to the core 😟 It’s a bit hard to keep the balance between the provided feature and and the amount of code we maintain here. It looks like it will not be a big problem for you to implement this ad-hoc feature in your solution, so you are not blocked.

Thanks again for your proposal!

[mrukas]

Its sad that this has not been built into the core. I have the exact same problem and have to use the workaround for now.