Recursive type substitution in TypeLibrary.MakeGenericType

engine/Sandbox.Reflection/TypeLibrary/TypeDescription.cs

@@ -647,6 +647,31 @@ public Type MakeGenericType( Type[] inargs )
 		if ( genericParams.Length != typeArgs.Length )
 			return null;
 
+
+		// Make a map from generic type parameters to type arguments
+		var substitutions = new Dictionary<Type, Type>();
+		for ( int i = 0; i < genericParams.Length; i++ )
+		{
+			var param = genericParams[i];
+			var arg = typeArgs[i];
+			substitutions.Add( param, arg );
+		}
+
+		// Substitutes generic type parameters in a type definition with type arguments
+		Type Substitute( Type type )
+		{
+			if ( !type.IsGenericType )
+				return type;
+			var genericDefinition = type.GetGenericTypeDefinition();
+			var genericParams = type.GenericTypeArguments;
+			for ( int i = 0; i < genericParams.Length; i++ )
+			{
+				if ( substitutions.TryGetValue( genericParams[i], out var substitutedType ) )
+					genericParams[i] = Substitute( substitutedType );
+			}
+			return genericDefinition.MakeGenericType( genericParams );
+		}
+
 		for ( int i = 0; i < genericParams.Length; i++ )
 		{
 			var param = genericParams[i];
@@ -691,7 +716,7 @@ public Type MakeGenericType( Type[] inargs )
 			var constraints = param.GetGenericParameterConstraints();
 			foreach ( var constraint in constraints )
 			{
-				if ( !constraint.IsAssignableFrom( arg ) )
+				if ( !Substitute( constraint ).IsAssignableFrom( arg ) )
 					return null;
 			}
 		}

engine/Sandbox.Test.Unit/Reflection/TypeLibraryTest.cs

@@ -340,6 +340,12 @@ public interface IConstraintBreaker<T>
 		void DoSomething( T value );
 	}
 
+	public interface IConstraintBreaker2<T, T2, T3>
+	{
+		void DoSomething( T value );
+		void DoSomething2( T2 value );
+		void DoSomething3( T3 value );
+	}
 
 
 	/// <summary>
@@ -360,6 +366,25 @@ public void ObeyGenericConstraints()
 									.CreateGeneric<IConstraintBreaker<TypeWrapper>>( [typeof( TypeWrapper )] );
 		Assert.IsNull( badboy );
 	}
+
+
+	/// <summary>
+	/// 
+	/// </summary>
+	[TestMethod]
+	public void ObeyRecursiveGenericConstraints()
+	{
+		var tl = new Sandbox.Internal.TypeLibrary();
+		tl.AddAssembly( ThisAssembly, true );
+
+		var goodboy = tl.GetType( typeof( ConstraintBreaker2<> ) )
+									.CreateGeneric<ConstraintBreaker2TypeErased>( [typeof( ConstraintBreaker2Inner )] );
+		Assert.IsNotNull( goodboy );
+
+		var badboy = tl.GetType( typeof( ConstraintBreaker2<> ) )
+									.CreateGeneric<ConstraintBreaker2TypeErased>( [typeof( TypeWrapper )] );
+		Assert.IsNull( badboy );
+	}
 }
 
 [Expose, MyType]
@@ -379,3 +404,40 @@ public void DoSomething( T value )
 
 	}
 }
+
+
+public class ConstraintBreaker2Inner :
+	IConstraintBreaker2<
+		ConstraintBreaker2Inner,
+		ConstraintBreaker2Inner,
+		ConstraintBreaker2Inner
+	>
+{
+	public void DoSomething( ConstraintBreaker2Inner value )
+	{
+
+	}
+
+	public void DoSomething2( ConstraintBreaker2Inner value )
+	{
+
+	}
+
+	public void DoSomething3( ConstraintBreaker2Inner value )
+	{
+
+	}
+}
+
+public class ConstraintBreaker2TypeErased { }
+
+[Expose]
+public class ConstraintBreaker2<T> : ConstraintBreaker2TypeErased where T : IConstraintBreaker2<T, T, T>
+{
+	public void DoSomething( T value )
+	{
+		value.DoSomething( value );
+		value.DoSomething2( value );
+		value.DoSomething3( value );
+	}
+}