Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

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

@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+
+namespace System.Data.Linq.SqlClient {
+    using System.Data.Linq;
+
+	/// <summary>
+	/// Turn CROSS APPLY into CROSS JOIN when the right side 
+	/// of the apply doesn't reference anything on the left side.
+	/// 
+	/// Any query which has a CROSS APPLY which cannot be converted to
+	/// a CROSS JOIN is annotated so that we can give a meaningful
+	/// error message later for SQL2K.
+	/// </summary>
+	internal class SqlCrossApplyToCrossJoin { 
+		internal static SqlNode Reduce(SqlNode node, SqlNodeAnnotations annotations) {
+			Reducer r = new Reducer();
+			r.Annotations = annotations;
+			return r.Visit(node);			
+		}
+
+		class Reducer : SqlVisitor {
+			internal SqlNodeAnnotations Annotations;
+
+			internal override SqlSource VisitJoin(SqlJoin join) {
+				if (join.JoinType == SqlJoinType.CrossApply) {
+					// Look down the left side to see what table aliases are produced.
+					HashSet<SqlAlias> p = SqlGatherProducedAliases.Gather(join.Left);
+					// Look down the right side to see what table aliases are consumed.
+					HashSet<SqlAlias> c = SqlGatherConsumedAliases.Gather(join.Right);
+					// Look at each consumed alias and see if they are mentioned in produced.
+                    if (p.Overlaps(c)) {
+						Annotations.Add(join, new SqlServerCompatibilityAnnotation(Strings.SourceExpressionAnnotation(join.SourceExpression), SqlProvider.ProviderMode.Sql2000));
+						// Can't reduce because this consumed alias is produced on the left.
+						return base.VisitJoin(join);
+					}
+
+					// Can turn this into a CROSS JOIN
+					join.JoinType = SqlJoinType.Cross;
+					return VisitJoin(join);
+				}
+				return base.VisitJoin(join);
+			}
+		}
+	}
+}