From 8e9f7fac3083cac3f412e30075d5f1069c681e69 Mon Sep 17 00:00:00 2001
From: Dan H <dan.r.hartley@gmail.com>
Date: Wed, 15 Jun 2022 22:32:48 +0100
Subject: [PATCH] Fixing issue where validation was applied to the
 ServiceDescriptor by the Azure Function Host DI container.

---
 .../ServiceCollectionExtensions.Decoration.cs |  2 +-
 src/Scrutor/ServiceDescriptorExtensions.cs    |  9 +++++---
 test/Scrutor.Tests/DecorationTests.cs         | 21 +++++++++++++++++++
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/src/Scrutor/ServiceCollectionExtensions.Decoration.cs b/src/Scrutor/ServiceCollectionExtensions.Decoration.cs
index 55375e5f..f53dfea3 100644
--- a/src/Scrutor/ServiceCollectionExtensions.Decoration.cs
+++ b/src/Scrutor/ServiceCollectionExtensions.Decoration.cs
@@ -263,7 +263,7 @@ public static bool TryDecorate(this IServiceCollection services, DecorationStrat
             var decoratedType = new DecoratedType(serviceDescriptor.ServiceType);
 
             // Insert decorated
-            services.Add(serviceDescriptor.WithServiceType(decoratedType));
+            services.Add(serviceDescriptor.WithDecoratedType(decoratedType));
 
             // Replace decorator
             services[i] = serviceDescriptor.WithImplementationFactory(strategy.CreateDecorator(decoratedType));
diff --git a/src/Scrutor/ServiceDescriptorExtensions.cs b/src/Scrutor/ServiceDescriptorExtensions.cs
index f734fe1d..dd03bf25 100644
--- a/src/Scrutor/ServiceDescriptorExtensions.cs
+++ b/src/Scrutor/ServiceDescriptorExtensions.cs
@@ -8,11 +8,14 @@ internal static class ServiceDescriptorExtensions
     public static ServiceDescriptor WithImplementationFactory(this ServiceDescriptor descriptor, Func<IServiceProvider, object> implementationFactory) => 
         new(descriptor.ServiceType, implementationFactory, descriptor.Lifetime);
 
-    public static ServiceDescriptor WithServiceType(this ServiceDescriptor descriptor, Type serviceType) => descriptor switch
+    public static ServiceDescriptor WithDecoratedType(this ServiceDescriptor descriptor, DecoratedType serviceType) => descriptor switch
     {
-        { ImplementationType: not null } => new ServiceDescriptor(serviceType, descriptor.ImplementationType, descriptor.Lifetime),
+        { ImplementationType: not null } => new ServiceDescriptor(serviceType, descriptor.ImplementationType.ToFactory(), descriptor.Lifetime),
         { ImplementationFactory: not null } => new ServiceDescriptor(serviceType, descriptor.ImplementationFactory, descriptor.Lifetime),
         { ImplementationInstance: not null } => new ServiceDescriptor(serviceType, descriptor.ImplementationInstance),
         _ => throw new ArgumentException($"No implementation factory or instance or type found for {descriptor.ServiceType}.", nameof(descriptor))
-    };
+    };
+
+    private static Func<IServiceProvider, object> ToFactory(this Type serviceType) => 
+        serviceProvider => ActivatorUtilities.CreateInstance(serviceProvider, serviceType);
 }
diff --git a/test/Scrutor.Tests/DecorationTests.cs b/test/Scrutor.Tests/DecorationTests.cs
index c75fdc6b..d7317e5a 100644
--- a/test/Scrutor.Tests/DecorationTests.cs
+++ b/test/Scrutor.Tests/DecorationTests.cs
@@ -229,6 +229,27 @@ public void Issue148_Decorate_IsAbleToDecorateConcreateTypes()
         Assert.NotNull(inner.Dependency);
     }
 
+    [Fact]
+    public void Issue171_Decorate_IsAbleToCreateValidRegistration()
+    {
+        var services = new ServiceCollection();
+
+        services
+            .AddTransient<IDecoratedService, Decorated>()
+            .Decorate<IDecoratedService, Decorator>();
+
+        foreach (var serviceDescriptor in services)
+        {
+            if (serviceDescriptor.ImplementationType != null
+                && serviceDescriptor.ServiceType != serviceDescriptor.ImplementationType)
+            {
+                var implementationTypeInterfaces = serviceDescriptor.ImplementationType.GetInterfaces();
+                var implementationAssignableToServiceType = implementationTypeInterfaces.Any(t => t == serviceDescriptor.ServiceType);
+                Assert.True(implementationAssignableToServiceType);
+            }
+        }
+    }
+
     #region Individual functions tests
 
     [Fact]