Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

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

@@ -0,0 +1,68 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace System.Data.Linq.SqlClient
+{
+    /// <summary>
+    /// Find referenced Aliases within a node.
+    /// </summary>
+    internal static class SqlAliasesReferenced
+    {
+        /// <summary>
+        /// Private visitor which walks the tree and looks for referenced aliases.
+        /// </summary>
+        private class Visitor : SqlVisitor {
+            internal IEnumerable<SqlAlias> aliases;
+            internal bool referencesAnyMatchingAliases = false;
+
+            internal override SqlNode Visit(SqlNode node) {
+                // Short-circuit when the answer is alreading known
+                if (this.referencesAnyMatchingAliases) {
+                    return node;
+                }
+                return base.Visit(node);
+            }
+
+            internal SqlAlias VisitAliasConsumed(SqlAlias a) {
+                if (a == null)
+                    return a;
+
+                bool match = false;
+                foreach (SqlAlias alias in aliases)
+                    if (alias == a) {
+                        match = true;
+                        break;
+                    }
+
+                if (match) {
+                    this.referencesAnyMatchingAliases = true;
+                }
+
+                return a;
+            }
+
+            internal override SqlExpression VisitColumn(SqlColumn col) {
+                VisitAliasConsumed(col.Alias);
+                VisitExpression(col.Expression);
+                return col;
+            }
+
+            internal override SqlExpression VisitColumnRef(SqlColumnRef cref) {
+                VisitAliasConsumed(cref.Column.Alias);
+                VisitExpression(cref.Column.Expression);
+                return cref;
+            }
+        }
+
+        /// <summary>
+        /// Returns true iff the given node references any aliases the list of 'aliases'.
+        /// </summary>
+        internal static bool ReferencesAny(SqlNode node, IEnumerable<SqlAlias> aliases) {
+            Visitor visitor = new Visitor();
+            visitor.aliases = aliases;
+            visitor.Visit(node);
+            return visitor.referencesAnyMatchingAliases;
+        }
+    }
+}