Proposal: IAsyncDisposable.ConfigureAwait(bool continueOnCapturedContext)

[stephentoub]

In https://github.com/dotnet/corefx/issues/32684, @jnm2 highlighted that in addition to ConfigureAwait on IAsyncEnumerable<T> (which we approved), we should also have it on IAsyncDisposable, so that you can write:

await using (asyncDisposable.ConfigureAwait(false))
{
    ...
}

Thus, the proposal is to add:

namespace System.Threading.Tasks
{
    public static class TaskExtensions // already exists and is where we put the extension for IAsyncEnumerable
    {
        public static ConfiguredAsyncDisposable ConfigureAwait(this IAsyncDisposable source, bool continueOnCapturedContext));
        ...
    }
}

namespace System.Runtime.CompilerServices
{
    public readonly struct ConfiguredAsyncDisposable
    {
        public ConfiguredValueTaskAwaitable DisposeAsync();
    }
}

[jcouv]

Hum, there's a compiler issue here too. await using currently only recognizes DisposeAsync that returns ValueTask. I'll loosen that to allow any awaitable.
Filed dotnet/roslyn#32707 (targeting preview3)

[jcouv]

Oops, never mind. It's the same issue we're already tracking (allow pattern-based disposal in async constructs). Tracked by dotnet/roslyn#32316