Ref struct in scanned assembly results in app crash at startup, if sa…

…gas are present (#7196)

* Fix ref struct scan for sagas (#7187)

* Prevent saga conventions from throwing on ref struct

* Better test

* Tweaks

---------

Co-authored-by: Mike Minutillo <mike.minutillo@particular.net>

* Handle .net framework

* Workaround for missing strongly typed check

* Update src/NServiceBus.Core/Sagas/Sagas.cs

Co-authored-by: Daniel Marbach <daniel.marbach@openplace.net>

* Use string equals

* Avoid null check

---------

Co-authored-by: Mike Minutillo <mike.minutillo@particular.net>
Co-authored-by: Daniel Marbach <daniel.marbach@openplace.net>

src/NServiceBus.AcceptanceTests/Core/Conventions/When_scanning_an_assembly_containing_a_ref_struct_and_sagas_enabled.cs

@@ -0,0 +1,57 @@
+namespace NServiceBus.AcceptanceTests.Core.Conventions
+{
+    using System;
+    using System.Threading.Tasks;
+    using AcceptanceTesting;
+    using EndpointTemplates;
+    using NServiceBus.AcceptanceTesting.Customization;
+    using NUnit.Framework;
+
+    public class When_scanning_an_assembly_containing_a_ref_struct_and_sagas_enabled : NServiceBusAcceptanceTest
+    {
+        [Test]
+        public void It_should_not_throw_an_exception()
+            => Assert.DoesNotThrowAsync(
+                () => Scenario.Define<ScenarioContext>()
+                    .WithEndpoint<EndpointWithASaga>()
+                    .Run()
+            );
+
+        // HINT: This will get picked up by the AssemblyRouteSource created by the routing call below
+        // Even though it is not a message type, it is still checked by passing it to conventions.
+        // The conventions added by Sagas were throwing an exception when passed a ref struct.
+        // See https://github.com/Particular/NServiceBus/issues/7179 for details.
+        ref struct RefStruct
+        {
+        }
+
+        class EndpointWithASaga : EndpointConfigurationBuilder
+        {
+            public EndpointWithASaga() => EndpointSetup<DefaultServer>(cfg => cfg
+                .ConfigureTransport()
+                .Routing()
+                .RouteToEndpoint(
+                    typeof(RefStruct).Assembly,
+                    Conventions.EndpointNamingConvention(typeof(EndpointWithASaga))
+                )
+            );
+            class RealSagaToSetUpConventions : Saga<RealSagaToSetUpConventions.RealSagaToSetUpConventionsSagaData>, IAmStartedByMessages<SomeMessage>
+            {
+                public Task Handle(SomeMessage message, IMessageHandlerContext context) => Task.CompletedTask;
+
+                protected override void ConfigureHowToFindSaga(SagaPropertyMapper<RealSagaToSetUpConventionsSagaData> mapper)
+                    => mapper.MapSaga(saga => saga.BusinessId).ToMessage<SomeMessage>(msg => msg.BusinessId);
+
+                public class RealSagaToSetUpConventionsSagaData : ContainSagaData
+                {
+                    public virtual Guid BusinessId { get; set; }
+                }
+            }
+        }
+
+        public class SomeMessage : IMessage
+        {
+            public Guid BusinessId { get; set; }
+        }
+    }
+}

src/NServiceBus.Core/Sagas/Sagas.cs

@@ -98,6 +98,13 @@ static bool IsCompatible(Type t, Type source)
 
         static bool IsTypeATimeoutHandledByAnySaga(Type type, IEnumerable<Type> sagas)
         {
+            // MakeGenericType() throws an exception if passed a ref struct type
+            // Messages cannot be ref struct types
+            if (type.CustomAttributes.Any(a => string.Equals(a.AttributeType.FullName, "System.Runtime.CompilerServices.IsByRefLikeAttribute")))
+            {
+                return false;
+            }
+
             var timeoutHandler = typeof(IHandleTimeouts<>).MakeGenericType(type);
             var messageHandler = typeof(IHandleMessages<>).MakeGenericType(type);