CS8600: Should report on methods that returns ConfiguredTaskAwaitable

[skarllot]

Version Used: Visual Studio 2019 Version 16.3.5

Steps to Reproduce:

static class TaskExtensions
{
    public static ConfiguredTaskAwaitable<TResult> NoSync<TResult>(this Task<TResult> task)
    {
        return task.ConfigureAwait(false);
    }
}

class Request
{
    public string? Name { get; }
    public Task<string?> GetName() => Task.FromResult(Name);
}

class Handler
{
    public async Task Handle(Request request)
    {
        string a = request.Name;    // <-- CS8600
        string b = await request.GetName().ConfigureAwait(false);    // <-- CS8600
        string c = await request.GetName().NoSync();    // <-- No warning here
    }
}

Expected Behavior:
CS8600 to be reported when using NoSync method extension.

Actual Behavior:
CS8600 is not reported when using NoSync method extension.

[skarllot]

Can I include a unit test for this case?

[jcouv]

@skarllot Sorry for late reply. Sure, feel free to add a unittest. It could go in NullableReferenceTypeTest.cs

[skarllot]

I wrote the tests and appears that the analyzer on master already fixed that issue.

[RikkiGibson]

Probably the same root cause as #40452, where awaiting a call to a nullable-reinterred generic method such as NoSync would cause us to analyze using the originally inferred type arguments (i.e. type arguments that are unaware of nullability).