Removing potential breaking changes

Author: fredericDelaporte

src/NHibernate/Engine/ISessionImplementor.cs

@@ -16,17 +16,24 @@
 
 namespace NHibernate.Engine
 {
-	// TODO: Convert to interface methods in 6.0
+	// 6.0 TODO: Convert to interface methods
 	internal static class SessionImplementorExtensions
 	{
 		internal static IDisposable BeginContext(this ISessionImplementor session)
 		{
-			return (session as AbstractSessionImpl)?.BeginContext();
+			if (session == null)
+				return null;
+			return (session as AbstractSessionImpl)?.BeginContext() ?? new SessionIdLoggingContext(session.SessionId);
 		}
 
 		internal static IDisposable BeginProcess(this ISessionImplementor session)
 		{
-			return (session as AbstractSessionImpl)?.BeginProcess();
+			if (session == null)
+				return null;
+			return (session as AbstractSessionImpl)?.BeginProcess() ??
+				// This method has only replaced bare call to setting the id, so this fallback is enough for avoiding a
+				// breaking change in case in custom session implementation is used.
+				new SessionIdLoggingContext(session.SessionId);
 		}
 	}
 
@@ -36,6 +43,7 @@ internal static IDisposable BeginProcess(this ISessionImplementor session)
 	/// </summary>
 	public partial interface ISessionImplementor
 	{
+		// 5.1 TODO: obsolete Initialize, it has no more usages.
 		/// <summary>
 		/// Initialize the session after its construction was complete
 		/// </summary>

src/NHibernate/Event/IEventSource.cs

@@ -40,12 +40,12 @@ public partial interface IEventSource : ISessionImplementor, ISession
 		/// <summary> Cascade delete an entity instance</summary>
 		void Delete(string entityName, object child, bool isCascadeDeleteEnabled, ISet<object> transientEntities);
 
+		// 6.0 TODO: yield null if already suspended.
 		/// <summary>
 		/// Suspend auto-flushing, yielding a disposable to dispose when auto flush should be restored. Supports
 		/// being called multiple times.
 		/// </summary>
-		/// <returns>A disposable to dispose when auto flush should be restored if it was not already suspended,
-		/// <see langword="null" /> otherwise.</returns>
+		/// <returns>A disposable to dispose when auto flush should be restored.</returns>
 		IDisposable SuspendAutoFlush();
 	}
 }

src/NHibernate/Impl/SessionImpl.cs

@@ -54,7 +54,7 @@ public sealed partial class SessionImpl : AbstractSessionImpl, IEventSource, ISe
 		private readonly ActionQueue actionQueue;
 
 		[NonSerialized]
-		private bool _suspendAutoFlush;
+		private int _suspendAutoFlushCount;
 
 		private readonly ConnectionManager connectionManager;
 
@@ -893,12 +893,12 @@ public void Delete(string entityName, object child, bool isCascadeDeleteEnabled,
 		}
 
 		/// <inheritdoc/>
-		public bool AutoFlushSuspended => _suspendAutoFlush;
+		public bool AutoFlushSuspended => _suspendAutoFlushCount > 0;
 
 		/// <inheritdoc/>
 		public IDisposable SuspendAutoFlush()
 		{
-			return _suspendAutoFlush ? null : new SuspendAutoFlushHelper(this);
+			return new SuspendAutoFlushHelper(this);
 		}
 
 		private sealed class SuspendAutoFlushHelper : IDisposable
@@ -908,14 +908,14 @@ private sealed class SuspendAutoFlushHelper : IDisposable
 			public SuspendAutoFlushHelper(SessionImpl session)
 			{
 				_session = session;
-				_session._suspendAutoFlush = true;
+				_session._suspendAutoFlushCount++;
 			}
 
 			public void Dispose()
 			{
 				if (_session == null)
 					throw new ObjectDisposedException("The auto-flush suspension helper has been disposed already");
-				_session._suspendAutoFlush = false;
+				_session._suspendAutoFlushCount --;
 				_session = null;
 			}
 		}
@@ -977,7 +977,7 @@ public void PersistOnFlush(object obj)
 
 		public override string BestGuessEntityName(object entity)
 		{
-			using (BeginProcess())
+			using (BeginContext())
 			{
 				if (entity.IsProxy())
 				{

src/NHibernate/Impl/StatelessSessionImpl.cs

@@ -358,7 +358,7 @@ public override FlushMode FlushMode
 
 		public override string BestGuessEntityName(object entity)
 		{
-			using (BeginProcess())
+			using (BeginContext())
 			{
 				if (entity.IsProxy())
 				{