Add simple backtracking support to pattern matching.

NRefactory/ICSharpCode.NRefactory/CSharp/Ast/AstNodeCollection.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using ICSharpCode.NRefactory.CSharp.PatternMatching;
 
@@ -156,29 +157,44 @@ namespace ICSharpCode.NRefactory.CSharp
 		
 		internal bool DoMatch(AstNodeCollection<T> other, Match match)
 		{
-			AstNode cur1 = this.node.FirstChild;
-			AstNode cur2 = other.node.FirstChild;
-			while (true) {
+			Stack<AstNode> patternStack = new Stack<AstNode>();
+			Stack<Pattern.PossibleMatch> stack = new Stack<Pattern.PossibleMatch>();
+			patternStack.Push(this.node.FirstChild);
+			stack.Push(new Pattern.PossibleMatch(other.node.FirstChild, match.CheckPoint()));
+			while (stack.Count > 0) {
+				AstNode cur1 = patternStack.Pop();
+				AstNode cur2 = stack.Peek().NextOther;
+				match.RestoreCheckPoint(stack.Pop().Checkpoint);
+				bool success = true;
+				while (cur1 != null && success) {
 					while (cur1 != null && cur1.Role != role)
 						cur1 = cur1.NextSibling;
 					while (cur2 != null && cur2.Role != role)
 						cur2 = cur2.NextSibling;
-				if (cur1 == null || cur2 == null)
+					if (cur1 == null)
 						break;
+					
 					Pattern pattern = cur1 as Pattern;
 					if (pattern == null && cur1.NodeType == NodeType.Pattern)
 						pattern = cur1.GetChildByRole(TypePlaceholder.ChildRole) as Pattern;
 					if (pattern != null) {
-					if (!pattern.DoMatchCollection(role, ref cur2, match))
-						return false;
+						Debug.Assert(stack.Count == patternStack.Count);
+						success = pattern.DoMatchCollection(role, cur2, match, stack);
+						Debug.Assert(stack.Count >= patternStack.Count);
+						while (stack.Count > patternStack.Count)
+							patternStack.Push(cur1.NextSibling);
 					} else {
-					if (!cur1.DoMatch(cur2, match))
-						return false;
-					cur2 = cur2.NextSibling;
+						success = cur1.DoMatch(cur2, match);
 					}
 					cur1 = cur1.NextSibling;
+					cur2 = cur2.NextSibling;
 				}
-			return cur1 == null && cur2 == null;
+				while (cur2 != null && cur2.Role != role)
+					cur2 = cur2.NextSibling;
+				if (success && cur2 == null)
+					return true;
+			}
+			return false;
 		}
 	}
 }

NRefactory/ICSharpCode.NRefactory/CSharp/Ast/PatternMatching/Backreference.cs

@@ -25,4 +25,28 @@ namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 			return match.Get(referencedGroupName).Last().Match(other) != null;
 		}
 	}
+	
+	/// <summary>
+	/// Matches identifier expressions that have the same identifier as the referenced variable/type definition/method definition.
+	/// </summary>
+	public class IdentifierExpressionBackreference : Pattern
+	{
+		readonly string referencedGroupName;
+		
+		public IdentifierExpressionBackreference(string referencedGroupName)
+		{
+			if (referencedGroupName == null)
+				throw new ArgumentNullException("referencedGroupName");
+			this.referencedGroupName = referencedGroupName;
+		}
+		
+		protected internal override bool DoMatch(AstNode other, Match match)
+		{
+			IdentifierExpression ident = other as IdentifierExpression;
+			if (ident == null || ident.TypeArguments.Any())
+				return false;
+			AstNode referenced = match.Get(referencedGroupName).Last();
+			return ident.Identifier == referenced.GetChildByRole(AstNode.Roles.Identifier).Name;
+		}
+	}
 }

NRefactory/ICSharpCode.NRefactory/CSharp/Ast/PatternMatching/Pattern.cs

@@ -2,6 +2,8 @@
 // This code is distributed under MIT X11 license (for details please see \doc\license.txt)
 
 using System;
+using System.Collections.Generic;
+using System.Diagnostics;
 
 namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 {
@@ -14,11 +16,21 @@ namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 			get { return NodeType.Pattern; }
 		}
 		
-		protected internal virtual bool DoMatchCollection(Role role, ref AstNode other, Match match)
+		internal struct PossibleMatch
 		{
-			bool result = DoMatch(other, match);
-			other = other.NextSibling;
-			return result;
+			public readonly AstNode NextOther; // next node after the last matched node
+			public readonly int Checkpoint; // checkpoint
+			
+			public PossibleMatch(AstNode nextOther, int checkpoint)
+			{
+				this.NextOther = nextOther;
+				this.Checkpoint = checkpoint;
+			}
+		}
+		
+		internal virtual bool DoMatchCollection(Role role, AstNode pos, Match match, Stack<PossibleMatch> backtrackingStack)
+		{
+			return DoMatch(pos, match);
 		}
 		
 		public override S AcceptVisitor<T, S>(IAstVisitor<T, S> visitor, T data)

NRefactory/ICSharpCode.NRefactory/CSharp/Ast/PatternMatching/Repeat.cs

@@ -2,6 +2,7 @@
 // This code is distributed under MIT X11 license (for details please see \doc\license.txt)
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 
 namespace ICSharpCode.NRefactory.CSharp.PatternMatching
@@ -20,24 +21,22 @@ namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 			AddChild(childNode, ElementRole);
 		}
 		
-		protected internal override bool DoMatchCollection(Role role, ref AstNode other, Match match)
+		internal override bool DoMatchCollection(Role role, AstNode pos, Match match, Stack<Pattern.PossibleMatch> backtrackingStack)
 		{
-			Debug.Assert(other != null && other.Role == role);
+			Debug.Assert(pos == null || pos.Role == role);
 			int matchCount = 0;
-			var lastValidCheckpoint = match.CheckPoint();
+			if (this.MinCount <= 0)
+				backtrackingStack.Push(new PossibleMatch(pos, match.CheckPoint()));
 			AstNode element = GetChildByRole(ElementRole);
-			AstNode pos = other;
-			while (pos != null && element.DoMatch(pos, match)) {
+			while (matchCount < this.MaxCount && pos != null && element.DoMatch(pos, match)) {
 				matchCount++;
-				lastValidCheckpoint = match.CheckPoint();
 				do {
 					pos = pos.NextSibling;
 				} while (pos != null && pos.Role != role);
-				// set 'other' (=pointer in collection) to the next node after the valid match
-				other = pos;
+				if (matchCount >= this.MinCount)
+					backtrackingStack.Push(new PossibleMatch(pos, match.CheckPoint()));
 			}
-			match.RestoreCheckPoint(lastValidCheckpoint); // restote old checkpoint after failed match
-			return matchCount >= MinCount && matchCount <= MaxCount;
+			return false; // never do a normal (single-element) match; always make the caller look at the results on the back-tracking stack.
 		}
 		
 		protected internal override bool DoMatch(AstNode other, Match match)
@@ -45,7 +44,7 @@ namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 			if (other == null || other.IsNull)
 				return this.MinCount <= 0;
 			else
-				return GetChildByRole(ElementRole).DoMatch(other, match);
+				return this.MaxCount >= 1 && GetChildByRole(ElementRole).DoMatch(other, match);
 		}
 	}
 }