tree.Root is side effecty

Author: bahusoid

src/NHibernate/Linq/IntermediateHqlTree.cs

@@ -127,6 +127,17 @@ public void AddFromClause(HqlTreeNode from)
 			_root.NodesPreOrder.OfType<HqlFrom>().First().AddChild(from);
 		}
 
+		internal HqlTreeNode GetFromNodeByAlias(string alias) =>
+			_root.NodesPreOrder
+			     .First(x => x.AstNode.Type == HqlSqlWalker.FROM).Children
+			     .First(x => GetNodeAlias(x) == alias);
+
+		private static string GetNodeAlias(HqlTreeNode fromNode) =>
+			fromNode.Children
+			        .Select(x => x.AstNode)
+			        .First(x => x.Type == HqlSqlWalker.ALIAS)
+			        .Text;
+
 		internal HqlRange GetFromRangeClause()
 		{
 			return _root.NodesPreOrder.OfType<HqlFrom>().First().Children.OfType<HqlRange>().FirstOrDefault();

src/NHibernate/Linq/Visitors/QuerySourceLocator.cs

@@ -5,7 +5,6 @@
 
 namespace NHibernate.Linq.Visitors
 {
-
 	public class QuerySourceLocator : NhQueryModelVisitorBase
 	{
 		readonly System.Type _type;

src/NHibernate/Linq/Visitors/ResultOperatorProcessors/ProcessFetch.cs

@@ -16,29 +16,14 @@ public void Process(FetchRequestBase resultOperator, QueryModelVisitor queryMode
 				queryModelVisitor.Model,
 				resultOperator.RelationMember.DeclaringType);
 			var name = queryModelVisitor.VisitorParameters.QuerySourceNamer.GetName(querySource);
-			Process(resultOperator, queryModelVisitor, tree, GetFromNodeByAlias(tree, name), name);
-		}
-
-		private static HqlTreeNode GetFromNodeByAlias(IntermediateHqlTree tree, string alias)
-		{
-			return tree.Root.NodesPreOrder
-				.First(x => x.AstNode.Type == HqlSqlWalker.FROM).Children
-				.First(x => GetNodeAlias(x) == alias);
-		}
-
-		private static string GetNodeAlias(HqlTreeNode fromNode)
-		{
-			return fromNode.Children
-				.Select(x => x.AstNode)
-				.First(x => x.Type == HqlSqlWalker.ALIAS)
-				.Text;
+			Process(resultOperator, queryModelVisitor, tree, tree.GetFromNodeByAlias(name), name);
 		}
 
 		// Since v5.5
 		[Obsolete("This method is not used and will be removed in a future version.")]
 		public void Process(FetchRequestBase resultOperator, QueryModelVisitor queryModelVisitor, IntermediateHqlTree tree, string sourceAlias)
 		{
-			Process(resultOperator, queryModelVisitor, tree, GetFromNodeByAlias(tree, sourceAlias), sourceAlias);
+			Process(resultOperator, queryModelVisitor, tree, tree.GetFromNodeByAlias(sourceAlias), sourceAlias);
 		}
 
 		private void Process(