TRLS014 — Use async method variant for async lambda

• Severity: Warning
• Category: Trellis

What it detects

Flags synchronous Trellis methods such as Map, Bind, Tap, Ensure, and TapOnFailure when any supplied lambda or method group does async work.

Why it matters

The sync method treats the returned Task or ValueTask as just another value. The async work does not get awaited by the Trellis pipeline.

Warning

This rule covers three cases: async lambdas, non-async lambdas whose converted return type is Task or ValueTask, and method groups returning Task or ValueTask.

Bad example

using System.Threading.Tasks;
using Trellis;

static class Example
{
    public static Result<Task<int>> Bad()
    {
        var result = Result.Success("Ada");
        return result.Map(LookupLengthAsync);
    }

    static Task<int> LookupLengthAsync(string value) =>
        Task.FromResult(value.Length);
}

Good example

using System.Threading.Tasks;
using Trellis;

static class Example
{
    public static Task<Result<int>> Good()
    {
        var result = Result.Success("Ada");
        return result.MapAsync(LookupLengthAsync);
    }

    static Task<int> LookupLengthAsync(string value) =>
        Task.FromResult(value.Length);
}

Code fix available

Yes — renames the sync API to the matching async API, such as MapAsync, BindAsync, TapAsync, EnsureAsync, or TapOnFailureAsync.

Configuration

Use standard Roslyn configuration if you need to suppress this rule in a specific scope.

dotnet_diagnostic.TRLS014.severity = none

#pragma warning disable TRLS014
// Intentional: documented exception or test-only pattern.
#pragma warning restore TRLS014

Tip

If the callback does async work, move to the matching async API immediately instead of returning a Task from the sync overload.