Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Data.Linq/SqlClient/Query/SqlRemoveConstantOrderBy.cs

@@ -0,0 +1,51 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Data;
+
+namespace System.Data.Linq.SqlClient {
+    using System.Data.Linq;
+
+    /// <summary>
+    /// SQL doesn't allow constants in ORDER BY.
+    /// 
+    /// Worse, an integer constant greater than 0 is treated as ORDER BY ProjectionColumn[i] so the results
+    /// can be unexpected.
+    /// 
+    /// The LINQ semantic for OrderBy(o=>constant) is for it to have no effect on the ordering. We enforce
+    /// that semantic here by removing all constant columns from OrderBy.
+    /// </summary>
+    internal class SqlRemoveConstantOrderBy {
+
+        private class Visitor : SqlVisitor {
+            internal override SqlSelect VisitSelect(SqlSelect select) {
+                int i = 0;
+                List<SqlOrderExpression> orders = select.OrderBy;
+                while (i < orders.Count) {
+                    SqlExpression expr = orders[i].Expression;
+                    while (expr.NodeType == SqlNodeType.DiscriminatedType) {
+                        expr = ((SqlDiscriminatedType)expr).Discriminator;
+                    }
+                    switch (expr.NodeType) {
+                        case SqlNodeType.Value:
+                        case SqlNodeType.Parameter:
+                            orders.RemoveAt(i);
+                            break;
+                        default:
+                            ++i;
+                            break;
+                    }
+                }
+                return base.VisitSelect(select);
+            }
+        }
+
+        /// <summary>
+        /// Remove relative constants from OrderBy.
+        /// </summary>
+        internal static SqlNode Remove(SqlNode node) {
+            return new Visitor().Visit(node);
+        }
+    }
+}