Register right function for Firebird and PostgreSQL (#2556)

Author: bahusoid

src/NHibernate.Test/Async/Legacy/SQLFunctionsTest.cs

@@ -121,8 +121,8 @@ public async Task DialectSQLFunctionsAsync()
 		public async Task LeftAndRightAsync()
 		{
 			//left or right functions are supported by most dialects but not registered.
-			if (!(Dialect is MsSql2000Dialect || Dialect is SQLiteDialect))
-				Assert.Ignore("left or right function is not supported by dialect");
+			AssumeFunctionSupported("left");
+			AssumeFunctionSupported("right");
 
 			using (var s = OpenSession())
 			using (var t = s.BeginTransaction())

src/NHibernate.Test/Legacy/SQLFunctionsTest.cs

@@ -110,8 +110,8 @@ public void DialectSQLFunctions()
 		public void LeftAndRight()
 		{
 			//left or right functions are supported by most dialects but not registered.
-			if (!(Dialect is MsSql2000Dialect || Dialect is SQLiteDialect))
-				Assert.Ignore("left or right function is not supported by dialect");
+			AssumeFunctionSupported("left");
+			AssumeFunctionSupported("right");
 
 			using (var s = OpenSession())
 			using (var t = s.BeginTransaction())

src/NHibernate/Dialect/FirebirdDialect.cs

@@ -525,6 +525,7 @@ private void RegisterStringAndCharFunctions()
 			RegisterFunction("locate", new PositionFunction());
 			RegisterFunction("replace", new StandardSafeSQLFunction("replace", NHibernateUtil.String, 3));
 			RegisterFunction("left", new StandardSQLFunction("left"));
+			RegisterFunction("right", new StandardSQLFunction("right"));
 		}
 
 		private void RegisterBlobFunctions()

src/NHibernate/Dialect/PostgreSQLDialect.cs

@@ -68,6 +68,7 @@ public PostgreSQLDialect()
 			RegisterFunction("iif", new IifSQLFunction());
 			RegisterFunction("replace", new StandardSQLFunction("replace", NHibernateUtil.String));
 			RegisterFunction("left", new SQLFunctionTemplate(NHibernateUtil.String, "substr(?1,1,?2)"));
+			RegisterFunction("right", new SQLFunctionTemplate(NHibernateUtil.String, "substr(?1, length(?1) + 1 -?2)"));
 			RegisterFunction("mod", new ModulusFunctionTemplate(true));
 
 			RegisterFunction("sign", new StandardSQLFunction("sign", NHibernateUtil.Int32));