Pattern Matching Idea

gistfile1.cs

var usingVarDecl = new VariableDeclarationStatement {
	Type = Pattern.Any("type"),
	Variables = {
		Pattern.NamedGroup(
			"variable",
			new VariableInitializer {
				Initializer = Pattern.Any()
			}
		)
	}
};
var usingTryCatch = new TryCatchStatement {
	TryBlock = Pattern.Any("body"),
	FinallyBlock = new BlockStatement {
		Statements = {
			new IfElseStatement {
				Condition = new BinaryOperatorExpression(
					Pattern.NamedGroup("ident", new IdentifierExpression()),
					BinaryOperatorType.InEquality,
					new NullReferenceExpression()
				),
				TrueStatement = new BlockStatement {
					Statements = {
						new ExpressionStatement(Pattern.Backreference("ident").ToExpression().Invoke("Dispose"))
					}
				}
			}
		}
	}
};
foreach (AstNode node in compilationUnit.Descendants.ToArray()) {
	Match m1 = usingVarDecl.Match(node);
	if (m1 == null) continue;
	Match m2 = usingTryCatch.Match(node.NextSibling);
	if (m2 == null) continue;
	if (m1.Single<VariableInitializer>("variable").Identifier == m2.Single<IdentifierExpression>("ident")) {
		BlockStatement body = m2.Single<BlockStatement>("body");
		body.Remove();
		node.NextSibling.Remove();
		node.ReplaceWith(
			varDecl => new UsingStatement {
				ResourceAcquisition = varDecl,
				EmbeddedStatement = body
			});
	}
}