Add compatibility changes to prevent Dialect properties from being null

Author: hazzik

src/NHibernate/Cfg/BindMappingEventArgs.cs

@@ -3,12 +3,16 @@
 
 namespace NHibernate.Cfg
 {
-	public class BindMappingEventArgs: EventArgs
+	public class BindMappingEventArgs : EventArgs
 	{
-		[Obsolete("Please use constructor without a dialect parameter.", true)]
-		public BindMappingEventArgs(Dialect.Dialect dialect, HbmMapping mapping, string fileName) : this(mapping, fileName)
+		//6.0 TODO: Remove
+		internal Lazy<Dialect.Dialect> LazyDialect;
+
+		[Obsolete("Please use constructor without a dialect parameter.")]
+		public BindMappingEventArgs(Dialect.Dialect dialect, HbmMapping mapping, string fileName)
+			: this(mapping, fileName)
 		{
-			Dialect = dialect;
+			LazyDialect = new Lazy<Dialect.Dialect>(() => dialect);
 		}
 
 		public BindMappingEventArgs(HbmMapping mapping, string fileName)
@@ -18,8 +22,8 @@ public BindMappingEventArgs(HbmMapping mapping, string fileName)
 		}
 
 		//Since v5.2
-		[Obsolete("This property will be removed in a future version.", true)]
-		public Dialect.Dialect Dialect { get; }
+		[Obsolete("This property will be removed in a future version.")]
+		public Dialect.Dialect Dialect => LazyDialect.Value;
 		public HbmMapping Mapping { get; }
 		public string FileName { get; }
 	}

src/NHibernate/Cfg/Configuration.cs

@@ -518,11 +518,12 @@ public void AddDeserializedMapping(HbmMapping mappingDocument, string documentFi
 			}
 			try
 			{
-				OnBeforeBindMapping(new BindMappingEventArgs(mappingDocument, documentFileName));
-				Mappings mappings = CreateMappings();
-
+				var dialect = new Lazy<Dialect.Dialect>(() => Dialect.Dialect.GetDialect(properties));
+				OnBeforeBindMapping(new BindMappingEventArgs(mappingDocument, documentFileName) {LazyDialect = dialect});
+				var mappings = CreateMappings();
+				mappings.LazyDialect = dialect;
 				new MappingRootBinder(mappings).Bind(mappingDocument);
-				OnAfterBindMapping(new BindMappingEventArgs(mappingDocument, documentFileName));
+				OnAfterBindMapping(new BindMappingEventArgs(mappingDocument, documentFileName) {LazyDialect = dialect});
 			}
 			catch (Exception e)
 			{
@@ -564,13 +565,11 @@ private void OnBeforeBindMapping(BindMappingEventArgs bindMappingEventArgs)
 		[Obsolete("Please use overload without a dialect parameter.")]
 		public Mappings CreateMappings(Dialect.Dialect dialect)
 		{
-			return CreateMappings();
+			var mappings = CreateMappings();
+			mappings.LazyDialect = new Lazy<Dialect.Dialect>(() => dialect);
+			return mappings;
 		}
 
-		/// <summary>
-		/// Create a new <see cref="Mappings" /> to add classes and collection
-		/// mappings to.
-		/// </summary>
 		public Mappings CreateMappings()
 		{
 			string defaultCatalog = PropertiesHelper.GetString(Environment.DefaultCatalog, properties, null);

src/NHibernate/Cfg/ConfigurationExtensions.cs

@@ -140,6 +140,7 @@ public static Configuration TypeDefinition<TDef>(this Configuration configuratio
 				return configuration;
 			}
 			var mappings = configuration.CreateMappings();
+			mappings.LazyDialect = new Lazy<Dialect.Dialect>(() => Dialect.Dialect.GetDialect(configuration.Properties));
 			mappings.AddTypeDef(tdConfiguration.Alias, typeof(TDef).AssemblyQualifiedName, tdConfiguration.Properties.ToTypeParameters());
 			return configuration;
 		}

src/NHibernate/Cfg/Mappings.cs

@@ -88,6 +88,9 @@ public sealed class PropertyReference
 		/// </summary>
 		protected internal IDictionary<string, TableDescription> tableNameBinding;
 
+		//6.0 TODO: Remove
+		internal Lazy<Dialect.Dialect> LazyDialect;
+
 		//Since v5.2
 		[Obsolete("Please use constructor without a dialect parameter.")]
 		protected internal Mappings(
@@ -138,7 +141,7 @@ protected internal Mappings(
 				defaultSchema,
 				preferPooledValuesLo)
 		{
-			Dialect = dialect;
+			LazyDialect = new Lazy<Dialect.Dialect>(() => dialect);
 		}
 
 		protected internal Mappings(
@@ -235,7 +238,7 @@ public PersistentClass GetClass(string className)
 
 		//Since v5.2
 		[Obsolete("This property will be removed in a future version.")]
-		public Dialect.Dialect Dialect { get; }
+		public Dialect.Dialect Dialect => LazyDialect.Value;
 
 		/// <summary>
 		/// 

src/NHibernate/Cfg/XmlHbmBinding/MappingRootBinder.cs

@@ -9,16 +9,11 @@ namespace NHibernate.Cfg.XmlHbmBinding
 {
 	public class MappingRootBinder : Binder
 	{
-		//Since v5.2
-		[Obsolete("This field will be removed in a future version.")]
-		private readonly Dialect.Dialect dialect;
-
 		//Since v5.2
 		[Obsolete("Please use constructor without a dialect parameter.")]
 		public MappingRootBinder(Mappings mappings, Dialect.Dialect dialect)
 			: this(mappings)
 		{
-			this.dialect = dialect;
 		}
 
 		public MappingRootBinder(Mappings mappings)