Support Func<> resolution

[pakrym]

No description provided.

[MitchRazga]

@pakrym Is this complete but just not published?

Played around with this branch earlier and Func<> resolution seemed to work as expected. Tests were passing too.

[MitchRazga]

Did run into one issue when multiple constructors use implicit funcs it will always choose the first one defined even if the service is not registered/optional. eg.

using Jab;
using System.Diagnostics;

internal class Program
{
	private static void Main(string[] args)
	{
		using Services services = new();
		IProvider<bool> provider = services.GetService<IProvider<bool>>();
	}
}

[ServiceProvider]
[Singleton(typeof(IProvider<>), typeof(Provider<>))]
//[Singleton(typeof(IService1<>), typeof(Service1<>))]
[Singleton(typeof(IService2<>), typeof(Service2<>))]
internal sealed partial class Services;

public interface IService1<T>;

public class Service1<T> : IService1<T>;

public interface IService2<T>;

public class Service2<T> : IService2<T>;

public interface IProvider<T>;

public class Provider<T> : IProvider<T>
{
	//public Provider(IService1<T> factory) => Debugger.Break();
	public Provider(Func<IService1<T>> factory) => Debugger.Break(); // Always hit even when not the best match
	//public Provider(Func<IService1<T>>? factory = null) => Debugger.Break(); // Same as above. Always hit.

	//public Provider(IService2<T> factory) => Debugger.Break();
	public Provider(Func<IService2<T>> factory) => Debugger.Break(); // Never hit unless moved above other constructors
}

[pakrym]

@MitchRazga this should work reasonably enough but I didn't have time for thorough testing.

I wonder is the constructor selection issue you see if related to funcs or a general bug.

[pakrym]

@eXpl0it3r / @MitchRazga / @sensslen any interest in push this over the finish line? :)

[MitchRazga]

Other than the multiple constructor issue mentioned above, it seemed pretty good as is.

I tried step-through debugging the source generator but still didn't have enough understanding to be able to fix it.

[MitchRazga]

Looks like in SelectConstructor that CanSatisfy always returns false for Func<> and will therefore fallback to the first/shortest constructor.

jab/src/Jab/ServiceProviderBuilder.cs

Lines 801 to 807 in 587703b

	// Pick a shortest candidate just in case we don't find
	// any applicable ctor and need to produce diagnostics
	if (candidate == null ||
	candidate.Parameters.Length > constructor.Parameters.Length)
	{
	candidate = constructor;
	}

jab/src/Jab/ServiceProviderBuilder.cs

Lines 830 to 831 in 587703b

	// Return a candidate so we can produce diagnostics for required services in a simple case
	return selectedCtor ?? candidate;

Might need to something here to first extract the service type from the Func<>

if (genericType != null &&
	SymbolEqualityComparer.Default.Equals(genericType.ConstructedFrom, _knownTypes.FuncType) &&
		genericType.TypeArguments[0] is INamedTypeSymbol funcServiceType)
{
	serviceType = funcServiceType;
}

Did a quick test offline and worked as expected. Tests were still passing too.