JIT: (bug) Runtime-async version of a Synchronized method releases the monitor twice, replacing the real exception and corrupting the caller's lock #133865

using System;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;

public class Program
{
    [MethodImpl(MethodImplOptions.Synchronized)]
    public Task Ret(Task t) => t;

    static async Task Caller(Program p, Task t)
    {
        await p.Ret(t);
    }

    public static int Main()
    {
        Program p = new Program();
        Task faulted = Task.FromException(new InvalidOperationException("boom"));
        try
        {
            Caller(p, faulted).GetAwaiter().GetResult();
        }
        catch (Exception e)
        {
            Console.WriteLine("caught: " + e.GetType().Name + ": " + e.Message);
        }

        // Second symptom: the extra release drops a lock the caller owns.
        Program p2 = new Program();
        Task faulted2 = Task.FromException(new InvalidOperationException("boom2"));
        lock (p2)
        {
            try
            {
                Caller(p2, faulted2).GetAwaiter().GetResult();
            }
            catch (Exception e)
            {
                Console.WriteLine("caught2: " + e.GetType().Name + ": " + e.Message);
            }
            Console.WriteLine("caller still holds its own lock: " + Monitor.IsEntered(p2));
        }
        return 100;
    }
}