fix: non-generic handler extending generic handler

Author: GerardSmit

src/Directory.Build.props

@@ -1,8 +1,8 @@
 <Project>
 
     <PropertyGroup>
-        <Version>1.0.0-alpha.22</Version>
-        <PackageVersion>1.0.0-alpha.22</PackageVersion>
+        <Version>1.0.0-alpha.23</Version>
+        <PackageVersion>1.0.0-alpha.23</PackageVersion>
         <Authors>Zapto</Authors>
         <RepositoryUrl>https://github.com/zapto-dev/Mediator</RepositoryUrl>
         <Copyright>Copyright © 2025 Zapto</Copyright>

src/Mediator.DependencyInjection/Generic/Handlers/GenericNotificationHandler.cs

@@ -102,7 +102,10 @@ public async ValueTask<bool> Handle(IServiceProvider provider, TNotification not
                 continue;
             }
 
-            var type = registration.HandlerType.MakeGenericType(arguments);
+            var type = registration.HandlerType.IsGenericType
+                ? registration.HandlerType.MakeGenericType(arguments)
+                : registration.HandlerType;
+            
             var handler = _serviceProvider.GetRequiredService(type);
 
             await ((INotificationHandler<TNotification>)handler!).Handle(provider, notification, ct);

src/Mediator.DependencyInjection/Generic/Handlers/GenericRequestHandler.cs

@@ -94,7 +94,10 @@ public async ValueTask<TResponse> Handle(IServiceProvider provider, TRequest req
                 continue;
             }
 
-            var type = registration.HandlerType.MakeGenericType(arguments);
+            var type = registration.HandlerType.IsGenericType
+                ? registration.HandlerType.MakeGenericType(arguments)
+                : registration.HandlerType;
+
             var handler = (IRequestHandler<TRequest, TResponse>) _serviceProvider.GetRequiredService(type);
 
             _cache.RequestHandlerType = type;

src/Mediator.DependencyInjection/Generic/Handlers/GenericStreamRequestHandler.cs

@@ -88,7 +88,10 @@ public IAsyncEnumerable<TResponse> Handle(IServiceProvider provider, TRequest re
                 continue;
             }
 
-            var type = registration.HandlerType.MakeGenericType(arguments);
+            var type = registration.HandlerType.IsGenericType
+                ? registration.HandlerType.MakeGenericType(arguments)
+                : registration.HandlerType;
+
             var handler = (IStreamRequestHandler<TRequest, TResponse>) _serviceProvider.GetRequiredService(type);
 
             _cache.RequestHandlerType = type;

tests/Mediator.DependencyInjection.Tests/Generics/NotificationGenericTest.cs

@@ -19,6 +19,7 @@ public async Task Valid()
 			{
 				b.AddNotificationHandler(typeof(GenericNotificationHandler<>));
 				b.AddNotificationHandler(typeof(GenericNotificationHandler<>));
+				b.AddNotificationHandler<StringGenericNotificationHandler>();
 			})
 			.AddSingleton(result)
 			.BuildServiceProvider();
@@ -27,14 +28,14 @@ await provider
 			.GetRequiredService<IMediator>()
 			.Publish(new GenericNotification<string?>(expected));
 
-		Assert.Equal(2, result.Values.Count);
+		Assert.Equal(3, result.Values.Count);
 		result.Values.Clear();
 
 		await provider
 			.GetRequiredService<IMediator>()
 			.Publish(new GenericNotification<string?>(null));
 
-		Assert.Equal(2, result.Values.Count);
+		Assert.Equal(3, result.Values.Count);
 	}
 
 	[Fact]

tests/Mediator.DependencyInjection.Tests/Generics/Notifications/StringGenericNotificationHandler.cs

@@ -0,0 +1,3 @@
+namespace Mediator.DependencyInjection.Tests.Generics;
+
+public class StringGenericNotificationHandler(Result result) : GenericNotificationHandler<string>(result);