Missing compiler warning for not awaiting Task produced by delegate?

[Youssef1313]

Version Used: main

Steps to Reproduce:

using System;
using System.Threading.Tasks;

internal delegate Task MyDelegate();

public class TestClass
{
    public void M()
    {
        MyDelegate c = async () =>
        {
            await Task.Delay(1);
            throw new Exception();
        };
        // Expecting to see: CS4014
        // warning CS4014: Because this call is not awaited, execution of the current method continues before the call is completed. Consider applying the 'await' operator to the result of the call.
        // But no warning is produced.
        c();
    }
}

If I switch to a local function instead of a delegate, the warning is correctly reported.

using System;
using System.Threading.Tasks;

internal delegate Task MyDelegate();


public class TestClass
{
    public void M()
    {
        async Task c()
        {
            await Task.Delay(1);
            throw new Exception();
        }
        c();
    }
}

[jaredpar]

The compiler is pretty conservative on when it will warn for missing await on a task-like type. The goal is to avoid introducing lots of warnings into code which is not async aware but does use Task APIs; originally a nod to compat with existing code. I'm unsure why the C# team decided to not warn on the first example in C# 5 but at this point there is very little chance that we would change this behavior.

[Youssef1313]

@jaredpar Not even in a warning wave?

[jaredpar]

Not for this. It's a pretty established pattern and code bases are sensitive to this warning.

[Youssef1313]

pretty established pattern

I'm surprised that people ended up doing it intentionally 😮 Exceptions could end up not being observed which is pretty bad. For context, we have had similar cases of Asserts being swallowed due to similar patterns.

FYI @Evangelink. I noticed it while working on microsoft/testfx#4640. The case in this issue isn't going to be caught by the analyzer I did as the delegate itself is async Task, but is called without await.