TRLS009: Incorrect async Result usage

Cause

Accessing Task<Result<T>> using blocking calls like .Result or .Wait() instead of using await.

Rule Description

Blocking on async operations can cause:

Deadlocks in UI applications or ASP.NET contexts
Thread pool starvation under load
Poor performance by blocking threads

When working with Task<Result<T>>, always use await to get the Result<T>.

How to Fix Violations

Use await instead of blocking:

// ❌ Bad - Blocking call (can deadlock!)
var result = GetCustomerAsync().Result;

// ✅ Good - Async/await
var result = await GetCustomerAsync();

Examples

Example 1: Accessing .Result

// ❌ Bad
public CustomerDto GetCustomer(Guid id)
{
    var result = customerService.GetCustomerAsync(id).Result;  // Deadlock risk!
    return result.Match(
        onSuccess: c => c.ToDto(),
        onFailure: _ => null);
}

// ✅ Good
public async Task<CustomerDto> GetCustomerAsync(Guid id)
{
    var result = await customerService.GetCustomerAsync(id);
    return result.Match(
        onSuccess: c => c.ToDto(),
        onFailure: _ => null);
}

Example 2: Accessing .Wait()

// ❌ Bad
public void ProcessCustomer(Guid id)
{
    var task = customerService.GetCustomerAsync(id);
    task.Wait();  // Deadlock risk!
    var result = task.Result;
    // ...
}

// ✅ Good
public async Task ProcessCustomerAsync(Guid id)
{
    var result = await customerService.GetCustomerAsync(id);
    // ...
}

Async Best Practices with Result

Use async/await all the way

// ✅ Good - Async all the way
public async Task<IActionResult> CreateCustomer(CreateCustomerDto dto)
{
    return await EmailAddress.TryCreate(dto.Email)
        .BindAsync(email => customerService.CreateAsync(email, dto.Name))
        .MapAsync(customer => customer.ToDto())
        .MatchAsync(
            onSuccess: dto => Ok(dto),
            onFailure: error => BadRequest(error));
}

Use ConfigureAwait in library code

// ✅ Library code - use ConfigureAwait(false)
public async Task<Result<Customer>> GetCustomerAsync(Guid id)
{
    var result = await repository
        .FindByIdAsync(id)
        .ConfigureAwait(false);
    
    return result.ToResult(
        Error.NotFound($"Customer {id} not found"));
}

When to Suppress Warnings

Never suppress this warning. If you absolutely must block (rare cases like Main method or console apps), use explicit synchronous methods instead of blocking on async methods.

None - this is a general async/await best practice.

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