How to implement ECS trigger collisions? (Unity.Physics 0.50)

I haven't seen any decent documentation about it and I haven't found any tutorials with ECS 0.50

It's all here: https://github.com/Unity-Technologies/EntityComponentSystemSamples

(.../triggers)

I suggest downloading the whole repo as there are quite a few interesting samples in there.

TriggerWarningAuthoring.cs:

 using Unity.Collections;
 using Unity.Entities;
 using Unity.Jobs;
 using Unity.Physics;
 using Unity.Physics.Systems;
 using UnityEngine;
 
 public class TriggerWarningAuthoring : MonoBehaviour, IConvertGameObjectToEntity
 {
     [SerializeField] string _message = "How dare you!";
     void IConvertGameObjectToEntity.Convert ( Entity e , EntityManager dst , GameObjectConversionSystem cs )
     {
         if( !enabled ) return;
 
         dst.AddComponentData( e , new TriggerWarning{
             Message = _message
         } );
     }
 }
 
 public struct TriggerWarning : IComponentData
 {
     public FixedString4096Bytes Message;
 }
 
 [Unity.Burst.BurstCompile]
 struct TriggerWarningJob : ITriggerEventsJob
 {
     [ReadOnly] public ComponentDataFromEntity<TriggerWarning> TriggerWarningData;
     public void Execute ( TriggerEvent evt )
     {
         Entity A = evt.EntityA;
         Entity B = evt.EntityB;
 
         if( TriggerWarningData.HasComponent(A) )
             Debug.Log($"a message: {TriggerWarningData[A].Message}");
         
         if( TriggerWarningData.HasComponent(B) );
             Debug.Log($"a message: {TriggerWarningData[B].Message}");
     }
 }
 
 [UpdateInGroup(typeof(FixedStepSimulationSystemGroup))]
 [UpdateAfter(typeof(ExportPhysicsWorld))]
 [UpdateBefore(typeof(EndFramePhysicsSystem))]
 public partial class TwitterSimulationSystem : SystemBase
 {
     StepPhysicsWorld _stepPhysicsWorldSystem;
     protected override void OnCreate ()
     {
         _stepPhysicsWorldSystem = World.GetOrCreateSystem<StepPhysicsWorld>();
 
         RequireForUpdate( GetEntityQuery( new EntityQueryDesc{
             All = new ComponentType[]{ typeof(TriggerWarning) }
         } ) );
     }
     protected override void OnStartRunning()
     {
         base.OnStartRunning();
         this.RegisterPhysicsRuntimeSystemReadOnly();
     }
     protected override void OnUpdate ()
     {
         var job = new TriggerWarningJob
         {
             TriggerWarningData = GetComponentDataFromEntity<TriggerWarning>( isReadOnly:true ) ,
         };
         Dependency = job.Schedule( _stepPhysicsWorldSystem.Simulation , Dependency );
     }
 }