TRLS008: Result is double-wrapped

Cause

A Result<Result<T>> type is detected, indicating that a Result is wrapped inside another Result.

Rule Description

Result<Result<T>> is almost always unintended and indicates a logic error. This typically happens when:

Using Map instead of Bind when the transformation returns a Result
Manually wrapping a Result in another Result

How to Fix Violations

Use Bind instead of Map

// ❌ Bad - Creates Result<Result<Customer>>
return emailResult.Map(email => Customer.Create(email));
//                                      ^^^^^^^^^^^^^^^^^^^
//                             Returns Result<Customer>

// ✅ Good - Flattens to Result<Customer>
return emailResult.Bind(email => Customer.Create(email));

Don't wrap existing Results

// ❌ Bad - Double wrapping
Result<Customer> customerResult = GetCustomer();
Result<Result<Customer>> wrapped = Result.Success(customerResult); // Wrong!

// ✅ Good - Return the Result directly
Result<Customer> customerResult = GetCustomer();
return customerResult;

Example

public Result<Order> CreateOrder(string emailStr, decimal amount)
{
    // ❌ Bad - Result<Result<Order>>
    var result = Email.TryCreate(emailStr)
        .Map(email => Order.Create(email, amount));
    //  ^^^                ^^^^^^^^^^^^^^^^^^^
    //  Map           Returns Result<Order>
    // Result is: Result<Result<Order>>

    // ✅ Good - Result<Order>
    var result = Email.TryCreate(emailStr)
        .Bind(email => Order.Create(email, amount));
    //  ^^^^
    //  Bind flattens the Result
}

When to Suppress Warnings

Do not suppress this warning. Result<Result<T>> is never the correct type.

If you have a legitimate case (extremely rare), restructure your code to use Bind or unwrap one layer.

TRLS002 - Use Bind instead of Map when lambda returns Result
TRLS012 - Maybe is double-wrapped

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