From 1dc249bf5c8f46216a871913f6d9931a91c59525 Mon Sep 17 00:00:00 2001
From: Bart Koelman <10324372+bkoelman@users.noreply.github.com>
Date: Wed, 28 Sep 2022 04:39:53 +0200
Subject: [PATCH] Improve error message when duplicate controllers are found,
 to include the fully qualified type names of the conflicting controllers

---
 src/JsonApiDotNetCore/Middleware/JsonApiRoutingConvention.cs | 3 ++-
 .../DuplicateResourceControllerTests.cs                      | 5 ++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/JsonApiDotNetCore/Middleware/JsonApiRoutingConvention.cs b/src/JsonApiDotNetCore/Middleware/JsonApiRoutingConvention.cs
index fe95d93446..58f8d18560 100644
--- a/src/JsonApiDotNetCore/Middleware/JsonApiRoutingConvention.cs
+++ b/src/JsonApiDotNetCore/Middleware/JsonApiRoutingConvention.cs
@@ -78,7 +78,8 @@ public void Apply(ApplicationModel application)
                     {
                         if (_controllerPerResourceTypeMap.ContainsKey(resourceType))
                         {
-                            throw new InvalidConfigurationException($"Multiple controllers found for resource type '{resourceType}'.");
+                            throw new InvalidConfigurationException(
+                                $"Multiple controllers found for resource type '{resourceType}': '{_controllerPerResourceTypeMap[resourceType].ControllerType}' and '{controller.ControllerType}'.");
                         }
 
                         _resourceTypePerControllerTypeMap.Add(controller.ControllerType, resourceType);
diff --git a/test/JsonApiDotNetCoreTests/IntegrationTests/NonJsonApiControllers/DuplicateResourceControllerTests.cs b/test/JsonApiDotNetCoreTests/IntegrationTests/NonJsonApiControllers/DuplicateResourceControllerTests.cs
index b130523588..0f1b1178f4 100644
--- a/test/JsonApiDotNetCoreTests/IntegrationTests/NonJsonApiControllers/DuplicateResourceControllerTests.cs
+++ b/test/JsonApiDotNetCoreTests/IntegrationTests/NonJsonApiControllers/DuplicateResourceControllerTests.cs
@@ -20,6 +20,9 @@ public void Fails_at_startup_when_multiple_controllers_exist_for_same_resource_t
         Action action = () => _ = Factory;
 
         // Assert
-        action.Should().ThrowExactly<InvalidConfigurationException>().WithMessage("Multiple controllers found for resource type 'knownResources'.");
+        InvalidConfigurationException exception = action.Should().ThrowExactly<InvalidConfigurationException>().Which!;
+        exception.Message.Should().StartWith("Multiple controllers found for resource type 'knownResources': ");
+        exception.Message.Should().Contain($"'{typeof(KnownResourcesController).FullName}'");
+        exception.Message.Should().Contain($"'{typeof(DuplicateKnownResourcesController).FullName}'");
     }
 }