System.BadImageFormatException: Bad IL Format when monitoring events on .NET Core 3.0-preview5

Description

FluentAssertions throws a BadImageFormatException when invoking a monitored event. This only occurs in the .NET Core 3.0 preview.

Complete minimal example reproducing the issue

[TestClass]
public class Repro
{
   public delegate void EventDelegate();

   public class Tester
   {
      public event EventDelegate TestEventDelegate;
      public event EventHandler TestEventHandler;

      public void RaiseEventDelegate()
      {
         TestEventDelegate?.Invoke();
      }

      public void RaiseEventHandler()
      {
         TestEventHandler?.Invoke( this, EventArgs.Empty );
      }
   }

   [TestMethod]
   public void TestRaiseEventDelegate()
   {
      var tester  = new Tester();
      var monitor = tester.Monitor();

      tester.RaiseEventDelegate();

      monitor.Should().Raise( nameof( Tester.TestEventDelegate ) );
   }

   [TestMethod]
   public void RaiseEventEventHandler()
   {
      var tester  = new Tester();
      var monitor = tester.Monitor();

      tester.RaiseEventHandler();

      monitor.Should().Raise( nameof( Tester.TestEventHandler ) );
   }
}

Expected behavior:

EventHandlerFactory should emit a handler that does not cause a BadImageFormatException to be thrown.

Actual behavior:

A BadImageFormatException is thrown when the event is invoked.

Versions

• Which version of Fluent Assertions are you using? FluentAssertions v5.6.0 via NuGet

• Which .NET runtime and version are you targeting? .NET Core 3.0-preview5

Additional Information

Have not looked into it. The exception is thrown immediately upon invoking the event. Bug does not occur in earlier versions of .NET Core (tested with 2.2).

[jnyrup]

Got it working by altering EventHandlerFactory.GenerateHandler in one of two ways:

a) Change from IEventRecorder to EventRecorder

MethodInfo methodToCall = typeof(IEventRecorder).GetMethod("RecordEvent",
    BindingFlags.Instance | BindingFlags.Public);

into

MethodInfo methodToCall = typeof(EventRecorder).GetMethod("RecordEvent",
    BindingFlags.Instance | BindingFlags.Public);

or b) change from OpCodes.Call to OpCodes.CallVirt

ilGen.EmitCall(OpCodes.Call, methodToCall, null);

into

ilGen.EmitCall(OpCodes.CallVirt, methodToCall, null);

[Wildenhaus]

Interface method calls will always be virtual, and the JIT can’t inline those, so technically Call should have been Callvirt (or IEventRecorder should have been strongly typed) in the first place.

~I’m not sure what has changed, but given the fix @jnyrup has found, I would assume that it has to do with more rigorous code checking on the part of RyuJIT.~

See dotnet/coreclr #24330