TeamCity.MSBuild.Logger/EventContext.cs

// ReSharper disable ClassNeverInstantiated.Global
namespace TeamCity.MSBuild.Logger
{
    using System;
    using JetBrains.Annotations;
    using Microsoft.Build.Framework;

    internal class EventContext : IEventRegistry, IEventContext
    {
        [CanBeNull] private BuildEventArgs _event;

        public IDisposable Register(BuildEventArgs buildEventArgs)
        {
            var prevEvent = _event;
            _event = buildEventArgs;
            return Disposable.Create(() => { _event = prevEvent; });
        }

        public bool TryGetEvent(out BuildEventArgs buildEventArgs)
        {
            if (_event != null)
            {
                buildEventArgs = _event;
                return true;
            }

            buildEventArgs = default;
            return false;
        }
    }
}