Fixing IServiceProvider.GetService implementation (fixes #376) (#377)

* Fixing IServiceProvider.GetService implementation (fixes #376)

* Added a configuration option to restore the old behavior if necessary

src/Ninject.Test/Integration/StandardKernelTests.cs

@@ -567,7 +567,40 @@ public void ItCanBeResolved()
             }
         }
     }
-
+
+    public class WhenServiceIsResolvedThroughServiceProviderInterface : StandardKernelContext
+    {
+        [Fact]
+        public void ItResolvesBoundService()
+        {
+            this.kernel.Bind<IWeapon>().To<Sword>();
+
+            var provider = this.kernel as IServiceProvider;
+            provider.GetService(typeof(IWeapon)).Should().NotBeNull();
+        }
+
+        [Fact]
+        public void ItReturnsNullWhenServiceIsNotConfigured()
+        {
+            var provider = this.kernel as IServiceProvider;
+            provider.GetService(typeof(Samurai)).Should().BeNull();
+        }
+
+        [Fact]
+        public void ItThrowsWhenServiceIsNotConfiguredAndSettingThrowOnGetServiceNotFound()
+        {
+            using (var kernel = new StandardKernel(new NinjectSettings
+            {
+                ThrowOnGetServiceNotFound = true
+            }))
+            {
+                var provider = kernel as IServiceProvider;
+                Action resolveAction = () => provider.GetService(typeof(Samurai));
+                resolveAction.Should().Throw<ActivationException>();
+            }
+        }
+    }
+
     public class InitializableA : IInitializable
     {
         public static int Count = 0;

src/Ninject/INinjectSettings.cs

@@ -123,5 +123,13 @@ public interface INinjectSettings
         /// is <see langword="true"/>.
         /// </value>
         bool PropertyInjection { get; set; }
+
+        /// <summary>
+        /// Gets or sets a value indicating whether the old (&lt;= 3.3.4) behavior of <see cref="IServiceProvider.GetService(Type)"/>
+        /// should be used which thorows an exception if the requested service cannot be found. Note that the documentation
+        /// of that method https://docs.microsoft.com/en-us/dotnet/api/system.iserviceprovider.getservice?view=netframework-4.6.2
+        /// states that the method should return <see langword="null"/> if there is no such service.
+        /// </summary>
+        bool ThrowOnGetServiceNotFound { get; set; }
     }
 }

src/Ninject/NinjectSettings.cs

@@ -166,5 +166,13 @@ public NinjectSettings()
         /// is <see langword="true"/>.
         /// </value>
         public bool PropertyInjection { get; set; }
+
+        /// <summary>
+        /// Gets or sets a value indicating whether the old (&lt;= 3.3.4) behavior of <see cref="IServiceProvider.GetService(Type)"/>
+        /// should be used which thorows an exception if the requested service cannot be found. Note that the documentation
+        /// of that method https://docs.microsoft.com/en-us/dotnet/api/system.iserviceprovider.getservice?view=netframework-4.6.2
+        /// states that the method should return <see langword="null"/> if there is no such service.
+        /// </summary>
+        public bool ThrowOnGetServiceNotFound { get; set; }
     }
 }

src/Ninject/ReadOnlyKernel.cs

@@ -246,7 +246,9 @@ public object GetService(Type serviceType)
         {
             Ensure.ArgumentNotNull(serviceType, nameof(serviceType));
 
-            return this.Get(serviceType);
+            return this.settings.ThrowOnGetServiceNotFound
+                ? this.Get(serviceType)
+                : this.TryGet(serviceType);
         }
 
         /// <summary>