unused-task-warning

When using dependency injection and async-await pattern it is possible to end up with an interface with a method that returns a Task. If this interface method is used in a synchronous method there is a likelihood that it will erroneously be run as a fire and forget method (which will not trigger inbuilt warning CS4014). In this situation this analyser generates a warning.

Can both be used as a Visual Studio extension or preferably as a project analyser available from NuGet.

Example:

using System.Threading.Tasks;

namespace AsyncAwaitProblem
{
	public interface ICallee
	{
		bool ProblemSolved { get; }
		Task SolveProblemAsync();
	}

	public class Callee : ICallee
	{
		public bool ProblemSolved { get; set; }

		public async Task SolveProblemAsync()
		{
			await Task.Delay(10);
			ProblemSolved = true;
		}
	}
	
	public class Caller
	{
		public bool DoCall()
		{
			ICallee xxx = new Callee();

			// This analyser will give a warning at the following line
			xxx.SolveProblemAsync(); // This is most likely an undesired fire and forget. 

			return xxx.ProblemSolved; // Will return false - we expected it to return true
		}
	}
}

Note that this analyser currently only checks for current known awaitable types (ex. types Task, ValueTask and ConfiguredTaskAwaitable (the type returned when using the ConfigureAwait method)). If another 'Awaitable' type is returned this analyser will not give the warning. This might be fixed in a future version.

Available from NuGet here: https://www.nuget.org/packages/Lindhart.Analyser.MissingAwaitWarning/

Available from Visual Studio marketplace here: https://marketplace.visualstudio.com/items?itemName=Lindhart.missingAwaitWarning#overview

For information on how to use analyzers check here: https://docs.microsoft.com/en-us/visualstudio/code-quality/roslyn-analyzers-overview?view=vs-2019