Make NHibernateUtil.Initialize / IsInitialized better reusable

- inferred ILazyInitializedCollection from IPersistentCollection
- changed NHibernateUtil.Initialize / IsInitialized to handle ILazyInitializedCollection

Author: DominicUllmann

src/NHibernate.Test/Async/NHSpecificTest/GH1515/Fixture.cs

@@ -0,0 +1,45 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by AsyncGenerator.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+
+using NHibernate.Collection;
+using NSubstitute;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH1515
+{
+	using System.Threading.Tasks;
+	using System.Threading;
+	[TestFixture]
+	public class FixtureAsync
+	{
+
+		[Test]
+		public async Task IntializeForwaredToLazyCollectionAsync()
+		{
+			var collection = Substitute.For<ILazyInitializedCollection>();
+
+			await (NHibernateUtil.InitializeAsync(collection));
+
+			await (collection.Received().ForceInitializationAsync(CancellationToken.None));
+		}
+
+		[Test]
+		public async Task IntializeForwaredToPersistentCollectionAsync()
+		{
+			var collection = Substitute.For<IPersistentCollection>();
+
+			await (NHibernateUtil.InitializeAsync(collection));
+
+			await (collection.Received().ForceInitializationAsync(CancellationToken.None));
+		}
+
+
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH1515/Fixture.cs

@@ -0,0 +1,52 @@
+using NHibernate.Collection;
+using NSubstitute;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH1515
+{
+	[TestFixture]
+	public class Fixture
+	{
+		[Test]
+		public void IsInitializedCallsWasInitializedFromLazyCollection()
+		{
+			var collection = Substitute.For<ILazyInitializedCollection>();
+
+			NHibernateUtil.IsInitialized(collection);
+
+			var assertRes = collection.Received().WasInitialized;
+		}
+
+		[Test]
+		public void IntializeForwaredToLazyCollection()
+		{
+			var collection = Substitute.For<ILazyInitializedCollection>();
+
+			NHibernateUtil.Initialize(collection);
+
+			collection.Received().ForceInitialization();
+		}
+
+		[Test]
+		public void IsInitializedCallsWasInitializedFromPersistentCollection()
+		{
+			var collection = Substitute.For<IPersistentCollection>();
+
+			NHibernateUtil.IsInitialized(collection);
+
+			var assertRes = collection.Received().WasInitialized;
+		}
+
+		[Test]
+		public void IntializeForwaredToPersistentCollection()
+		{
+			var collection = Substitute.For<IPersistentCollection>();
+
+			NHibernateUtil.Initialize(collection);
+
+			collection.Received().ForceInitialization();
+		}
+
+
+	}
+}

src/NHibernate/Async/Collection/AbstractPersistentCollection.cs

@@ -24,7 +24,7 @@ namespace NHibernate.Collection
 {
 	using System.Threading.Tasks;
 	using System.Threading;
-	public abstract partial class AbstractPersistentCollection : IPersistentCollection
+	public abstract partial class AbstractPersistentCollection : IPersistentCollection, ILazyInitializedCollection
 	{
 
 		/// <summary>

src/NHibernate/Async/Collection/ILazyInitializedCollection.cs

@@ -0,0 +1,25 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by AsyncGenerator.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+
+namespace NHibernate.Collection
+{
+	using System.Threading.Tasks;
+	using System.Threading;
+	public partial interface ILazyInitializedCollection
+	{
+
+		/// <summary>
+		/// Force immediate initialization.
+		/// </summary>
+		/// <param name="cancellationToken">A cancellation token that can be used to cancel the work</param>
+		Task ForceInitializationAsync(CancellationToken cancellationToken);
+
+	}
+}

src/NHibernate/Async/NHibernateUtil.cs

@@ -48,11 +48,17 @@ public static partial class NHibernateUtil
 				{
 					return ((INHibernateProxy)proxy).HibernateLazyInitializer.InitializeAsync(cancellationToken);
 				}
-				else if (proxy is IPersistentCollection coll)
+				else if (proxy is ILazyInitializedCollection coll)
 				{
 					return coll.ForceInitializationAsync(cancellationToken);
 				}
+				// 6.0 TODO: remove once IPersistentCollection derives from ILazyInitializedCollection
+				else if (proxy is IPersistentCollection persistent)
+				{
+					return persistent.ForceInitializationAsync(cancellationToken);
+				}
 				return Task.CompletedTask;
+
 			}
 			catch (Exception ex)
 			{

src/NHibernate/Collection/AbstractPersistentCollection.cs

@@ -15,8 +15,9 @@ namespace NHibernate.Collection
 	/// <summary>
 	/// Base class for implementing <see cref="IPersistentCollection"/>.
 	/// </summary>
+	// 6.0 TODO: remove ILazyInitializedCollection once IPersistentCollection derives from it
 	[Serializable]
-	public abstract partial class AbstractPersistentCollection : IPersistentCollection
+	public abstract partial class AbstractPersistentCollection : IPersistentCollection, ILazyInitializedCollection
 	{
 		protected internal static readonly object Unknown = new object(); //place holder
 		protected internal static readonly object NotFound = new object(); //place holder

src/NHibernate/Collection/ILazyInitializedCollection.cs

@@ -0,0 +1,27 @@
+namespace NHibernate.Collection
+{
+	/// <summary>
+	/// This interface allows to check if a lazy collection is already initialized and to force its initialization.
+	/// </summary>
+	/// <remarks>
+	/// This interface is provided to allow implementing lazy initialized collections which do not implement
+	/// <see cref="IPersistentCollection" />.
+	/// That is e.g. needed for NHibernate.Envers which can't load its collections as PersistentCollections.
+	/// </remarks>
+	// 6.0 TODO: set as ancestor of IPersistentCollection
+	public partial interface ILazyInitializedCollection
+	{
+		/// <summary>
+		/// Return <see langword="true"/> if the proxy has already been initialized.
+		/// If <see langword="false"/>, accessing the collection or calling <see cref="ForceInitialization" />
+		/// initializes the collection.
+		/// </summary>
+		bool WasInitialized { get; }
+
+		/// <summary>
+		/// Force immediate initialization.
+		/// </summary>
+		void ForceInitialization();
+
+	}
+}

src/NHibernate/NHibernateUtil.cs

@@ -382,10 +382,16 @@ public static void Initialize(object proxy)
 			{
 				((INHibernateProxy)proxy).HibernateLazyInitializer.Initialize();
 			}
-			else if (proxy is IPersistentCollection coll)
+			else if (proxy is ILazyInitializedCollection coll)
 			{
 				coll.ForceInitialization();
 			}
+			// 6.0 TODO: remove once IPersistentCollection derives from ILazyInitializedCollection
+			else if (proxy is IPersistentCollection persistent)
+			{
+				persistent.ForceInitialization();
+			}
+
 		}
 
 		/// <summary>
@@ -399,9 +405,14 @@ public static bool IsInitialized(object proxy)
 			{
 				return !((INHibernateProxy)proxy).HibernateLazyInitializer.IsUninitialized;
 			}
-			else if (proxy is IPersistentCollection)
+			else if (proxy is ILazyInitializedCollection coll)
+			{
+				return coll.WasInitialized;
+			}
+			// 6.0 TODO: remove once IPersistentCollection derives from ILazyInitializedCollection
+			else if (proxy is IPersistentCollection persistent)
 			{
-				return ((IPersistentCollection)proxy).WasInitialized;
+				return persistent.WasInitialized;
 			}
 			else
 			{