Add OptionalNode for pattern matching.

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

@@ -17,6 +17,7 @@ namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 		S VisitChoice(Choice choice, T data);
 		S VisitNamedNode(NamedNode namedNode, T data);
 		S VisitRepeat(Repeat repeat, T data);
+		S VisitOptionalNode(OptionalNode optionalNode, T data);
 		S VisitIdentifierExpressionBackreference(IdentifierExpressionBackreference identifierExpressionBackreference, T data);
 	}
 }

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

@@ -0,0 +1,42 @@
+// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
+// 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
+{
+	public class OptionalNode : Pattern
+	{
+		public static readonly Role<AstNode> ElementRole = new Role<AstNode>("Element", AstNode.Null);
+		
+		public OptionalNode(AstNode childNode)
+		{
+			AddChild(childNode, ElementRole);
+		}
+		
+		public OptionalNode(string groupName, AstNode childNode) : this(new NamedNode(groupName, childNode))
+		{
+		}
+		
+		internal override bool DoMatchCollection(Role role, AstNode pos, Match match, Stack<Pattern.PossibleMatch> backtrackingStack)
+		{
+			backtrackingStack.Push(new PossibleMatch(pos, match.CheckPoint()));
+			return GetChildByRole(ElementRole).DoMatch(pos, match);
+		}
+		
+		protected internal override bool DoMatch(AstNode other, Match match)
+		{
+			if (other == null || other.IsNull)
+				return true;
+			else
+				return GetChildByRole(ElementRole).DoMatch(other, match);
+		}
+		
+		public override S AcceptVisitor<T, S>(IAstVisitor<T, S> visitor, T data)
+		{
+			return ((IPatternAstVisitor<T, S>)visitor).VisitOptionalNode(this, data);
+		}
+	}
+}

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

@@ -74,6 +74,11 @@ namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 			return p != null ? new AttributeSectionPlaceholder(p) : null;
 		}
 		
+		public static implicit operator SwitchSection(Pattern p)
+		{
+			return p != null ? new SwitchSectionPlaceholder(p) : null;
+		}
+		
 		// Make debugging easier by giving Patterns a ToString() implementation
 		public override string ToString()
 		{

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

@@ -181,4 +181,33 @@ namespace ICSharpCode.NRefactory.CSharp.PatternMatching
 			return child.DoMatchCollection(role, pos, match, backtrackingStack);
 		}
 	}
+	
+	sealed class SwitchSectionPlaceholder : SwitchSection
+	{
+		readonly AstNode child;
+		
+		public SwitchSectionPlaceholder(AstNode child)
+		{
+			this.child = child;
+		}
+		
+		public override NodeType NodeType {
+			get { return NodeType.Placeholder; }
+		}
+		
+		public override S AcceptVisitor<T, S>(IAstVisitor<T, S> visitor, T data)
+		{
+			return ((IPatternAstVisitor<T, S>)visitor).VisitPlaceholder(this, child, data);
+		}
+		
+		protected internal override bool DoMatch(AstNode other, Match match)
+		{
+			return child.DoMatch(other, match);
+		}
+		
+		internal override bool DoMatchCollection(Role role, AstNode pos, Match match, Stack<Pattern.PossibleMatch> backtrackingStack)
+		{
+			return child.DoMatchCollection(role, pos, match, backtrackingStack);
+		}
+	}
 }

NRefactory/ICSharpCode.NRefactory/CSharp/OutputVisitor/OutputVisitor.cs

@@ -2170,6 +2170,16 @@ namespace ICSharpCode.NRefactory.CSharp
 			RPar();
 			return EndNode(repeat);
 		}
+		
+		object IPatternAstVisitor<object, object>.VisitOptionalNode(OptionalNode optionalNode, object data)
+		{
+			StartNode(optionalNode);
+			WriteKeyword("optional");
+			LPar();
+			optionalNode.GetChildByRole(OptionalNode.ElementRole).AcceptVisitor(this, data);
+			RPar();
+			return EndNode(optionalNode);
+		}
 		#endregion
 	}
 }

NRefactory/ICSharpCode.NRefactory/ICSharpCode.NRefactory.csproj

@@ -107,6 +107,7 @@
     <Compile Include="CSharp\Ast\PatternMatching\IPatternAstVisitor.cs" />
     <Compile Include="CSharp\Ast\PatternMatching\Match.cs" />
     <Compile Include="CSharp\Ast\PatternMatching\NamedNode.cs" />
+    <Compile Include="CSharp\Ast\PatternMatching\OptionalNode.cs" />
     <Compile Include="CSharp\Ast\PatternMatching\Repeat.cs" />
     <Compile Include="CSharp\Ast\PatternMatching\Pattern.cs" />
     <Compile Include="CSharp\Ast\PatternMatching\Placeholder.cs" />