fix #436 - Incorrectly deducing that some uses of using, MoveNext() and Current can be rewritten as foreach when they cannot.

ICSharpCode.Decompiler/Ast/Transforms/PatternStatementTransform.cs

@@ -419,6 +419,12 @@ namespace ICSharpCode.Decompiler.Ast.Transforms
 			// We just care that we can move it in front of the loop:
 			if (declarationPoint != loop)
 				return null;
+
+			// Make sure that the enumerator variable is not used inside the body
+			foreach (Statement stmt in m.Get<Statement>("statement")) {
+				if (UsesEnumerator(stmt, enumeratorVar.Name))
+					return null;
+			}
 			
 			BlockStatement newBody = new BlockStatement();
 			foreach (Statement stmt in m.Get<Statement>("variablesInsideLoop"))
@@ -1160,5 +1166,40 @@ namespace ICSharpCode.Decompiler.Ast.Transforms
 			return null;
 		}
 		#endregion
+
+		#region UsesEnumerator helper
+		class UsesEnumeratorVisitor : DepthFirstAstVisitor<bool>
+		{
+			Identifier enumeratorIdentifier;
+			
+			public UsesEnumeratorVisitor(string identifier)
+			{
+				enumeratorIdentifier = Identifier.Create(identifier);
+			}
+
+			protected override bool VisitChildren(AstNode node)
+			{
+				AstNode next;
+				for (var child = node.FirstChild; child != null; child = next) {
+					// Store next to allow the loop to continue
+					// if the visitor removes/replaces child.
+					next = child.NextSibling;
+					if (child.AcceptVisitor(this))
+						return true;
+				}
+				return false;
+			}
+
+			public override bool VisitIdentifier(Identifier identifier)
+			{
+				return identifier.IsMatch(enumeratorIdentifier);
+			}
+		}
+
+		bool UsesEnumerator(Statement statement, string enumeratorVarName)
+		{
+			return statement.AcceptVisitor(new UsesEnumeratorVisitor(enumeratorVarName));
+		}
+		#endregion
 	}
 }