Add support for IServiceProviderIsService (#54047)

* Add support for IServiceProviderIsService
- This optional service lets consumers query to see if a service is resolvable without side effects (not having to explicitly resolve the service).
- Added new spec tests to verify the baseline behavior based on IServiceCollection features.
- Handle built in services as part of IsServce
- Special case built in services as part of the IsService check
- Make the tests part of the core DI tests and enable skipping via a property

Co-authored-by: Travis Illig <tillig@paraesthesia.com>

Author: davidfowl

src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.cs

@@ -36,6 +36,10 @@ public partial interface IServiceProviderFactory<TContainerBuilder> where TConta
         TContainerBuilder CreateBuilder(Microsoft.Extensions.DependencyInjection.IServiceCollection services);
         System.IServiceProvider CreateServiceProvider(TContainerBuilder containerBuilder);
     }
+    public partial interface IServiceProviderIsService
+    {
+        bool IsService(System.Type serviceType);
+    }
     public partial interface IServiceScope : System.IDisposable
     {
         System.IServiceProvider ServiceProvider { get; }

src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/IServiceProviderIsService.cs

@@ -0,0 +1,20 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+namespace Microsoft.Extensions.DependencyInjection
+{
+    /// <summary>
+    /// Optional service used to determine if the specified type is available from the <see cref="IServiceProvider"/>.
+    /// </summary>
+    public interface IServiceProviderIsService
+    {
+        /// <summary>
+        /// Determines if the specified service type is available from the <see cref="IServiceProvider"/>.
+        /// </summary>
+        /// <param name="serviceType">An object that specifies the type of service object to test.</param>
+        /// <returns>true if the specified service is a available, false if it is not.</returns>
+        bool IsService(Type serviceType);
+    }
+}

src/libraries/Microsoft.Extensions.DependencyInjection.Specification.Tests/src/ServiceProviderIsServiceSpecificationTests.cs

@@ -0,0 +1,127 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Microsoft.Extensions.DependencyInjection.Specification.Fakes;
+using Xunit;
+
+namespace Microsoft.Extensions.DependencyInjection.Specification
+{
+    public abstract partial class DependencyInjectionSpecificationTests
+    {
+        public virtual bool SupportsIServiceProviderIsService => true;
+
+        [Fact]
+        public void ExplictServiceRegisterationWithIsService()
+        {
+            if (!SupportsIServiceProviderIsService)
+            {
+                return;
+            }
+
+            // Arrange
+            var collection = new TestServiceCollection();
+            collection.AddTransient(typeof(IFakeService), typeof(FakeService));
+            var provider = CreateServiceProvider(collection);
+
+            // Act
+            var serviceProviderIsService = provider.GetService<IServiceProviderIsService>();
+
+            // Assert
+            Assert.NotNull(serviceProviderIsService);
+            Assert.True(serviceProviderIsService.IsService(typeof(IFakeService)));
+            Assert.False(serviceProviderIsService.IsService(typeof(FakeService)));
+        }
+
+        [Fact]
+        public void OpenGenericsWithIsService()
+        {
+            if (!SupportsIServiceProviderIsService)
+            {
+                return;
+            }
+
+            // Arrange
+            var collection = new TestServiceCollection();
+            collection.AddTransient(typeof(IFakeOpenGenericService<>), typeof(FakeOpenGenericService<>));
+            var provider = CreateServiceProvider(collection);
+
+            // Act
+            var serviceProviderIsService = provider.GetService<IServiceProviderIsService>();
+
+            // Assert
+            Assert.NotNull(serviceProviderIsService);
+            Assert.True(serviceProviderIsService.IsService(typeof(IFakeOpenGenericService<IFakeService>)));
+            Assert.False(serviceProviderIsService.IsService(typeof(IFakeOpenGenericService<>)));
+        }
+
+        [Fact]
+        public void ClosedGenericsWithIsService()
+        {
+            if (!SupportsIServiceProviderIsService)
+            {
+                return;
+            }
+
+            // Arrange
+            var collection = new TestServiceCollection();
+            collection.AddTransient(typeof(IFakeOpenGenericService<IFakeService>), typeof(FakeOpenGenericService<IFakeService>));
+            var provider = CreateServiceProvider(collection);
+
+            // Act
+            var serviceProviderIsService = provider.GetService<IServiceProviderIsService>();
+
+            // Assert
+            Assert.NotNull(serviceProviderIsService);
+            Assert.True(serviceProviderIsService.IsService(typeof(IFakeOpenGenericService<IFakeService>)));
+        }
+
+        [Fact]
+        public void IEnumerableWithIsServiceAlwaysReturnsTrue()
+        {
+            if (!SupportsIServiceProviderIsService)
+            {
+                return;
+            }
+
+            // Arrange
+            var collection = new TestServiceCollection();
+            collection.AddTransient(typeof(IFakeService), typeof(FakeService));
+            var provider = CreateServiceProvider(collection);
+
+            // Act
+            var serviceProviderIsService = provider.GetService<IServiceProviderIsService>();
+
+            // Assert
+            Assert.NotNull(serviceProviderIsService);
+            Assert.True(serviceProviderIsService.IsService(typeof(IEnumerable<IFakeService>)));
+            Assert.True(serviceProviderIsService.IsService(typeof(IEnumerable<FakeService>)));
+            Assert.False(serviceProviderIsService.IsService(typeof(IEnumerable<>)));
+        }
+
+        [Fact]
+        public void BuiltInServicesWithIsServiceReturnsTrue()
+        {
+            if (!SupportsIServiceProviderIsService)
+            {
+                return;
+            }
+
+            // Arrange
+            var collection = new TestServiceCollection();
+            collection.AddTransient(typeof(IFakeService), typeof(FakeService));
+            var provider = CreateServiceProvider(collection);
+
+            // Act
+            var serviceProviderIsService = provider.GetService<IServiceProviderIsService>();
+
+            // Assert
+            Assert.NotNull(serviceProviderIsService);
+            Assert.True(serviceProviderIsService.IsService(typeof(IServiceProvider)));
+            Assert.True(serviceProviderIsService.IsService(typeof(IServiceScopeFactory)));
+            Assert.True(serviceProviderIsService.IsService(typeof(IServiceProviderIsService)));
+        }
+    }
+}

src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/CallSiteFactory.cs

@@ -12,7 +12,7 @@
 
 namespace Microsoft.Extensions.DependencyInjection.ServiceLookup
 {
-    internal sealed class CallSiteFactory
+    internal sealed class CallSiteFactory : IServiceProviderIsService
     {
         private const int DefaultSlot = 0;
         private readonly ServiceDescriptor[] _descriptors;
@@ -441,6 +441,38 @@ public void Add(Type type, ServiceCallSite serviceCallSite)
             _callSiteCache[new ServiceCacheKey(type, DefaultSlot)] = serviceCallSite;
         }
 
+        public bool IsService(Type serviceType)
+        {
+            if (serviceType is null)
+            {
+                throw new ArgumentNullException(nameof(serviceType));
+            }
+
+            // Querying for an open generic should return false (they aren't resolvable)
+            if (serviceType.IsGenericTypeDefinition)
+            {
+                return false;
+            }
+
+            if (_descriptorLookup.ContainsKey(serviceType))
+            {
+                return true;
+            }
+
+            if (serviceType.IsConstructedGenericType && serviceType.GetGenericTypeDefinition() is Type genericDefinition)
+            {
+                // We special case IEnumerable since it isn't explicitly registered in the container
+                // yet we can manifest instances of it when requested.
+                return genericDefinition == typeof(IEnumerable<>) || _descriptorLookup.ContainsKey(genericDefinition);
+            }
+
+            // These are the built in service types that aren't part of the list of service descriptors
+            // If you update these make sure to also update the code in ServiceProvider.ctor
+            return serviceType == typeof(IServiceProvider) ||
+                   serviceType == typeof(IServiceScopeFactory) ||
+                   serviceType == typeof(IServiceProviderIsService);
+        }
+
         private struct ServiceDescriptorCacheItem
         {
             private ServiceDescriptor _item;

src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceProvider.cs

@@ -38,8 +38,11 @@ internal ServiceProvider(IEnumerable<ServiceDescriptor> serviceDescriptors, Serv
 
             Root = new ServiceProviderEngineScope(this);
             CallSiteFactory = new CallSiteFactory(serviceDescriptors);
+            // The list of built in services that aren't part of the list of service descriptors
+            // keep this in sync with CallSiteFactory.IsService
             CallSiteFactory.Add(typeof(IServiceProvider), new ServiceProviderCallSite());
             CallSiteFactory.Add(typeof(IServiceScopeFactory), new ServiceScopeFactoryCallSite(Root));
+            CallSiteFactory.Add(typeof(IServiceProviderIsService), new ConstantCallSite(typeof(IServiceProviderIsService), CallSiteFactory));
 
             if (options.ValidateScopes)
             {
@@ -111,7 +114,9 @@ internal object GetService(Type serviceType, ServiceProviderEngineScope serviceP
             Func<ServiceProviderEngineScope, object> realizedService = _realizedServices.GetOrAdd(serviceType, _createServiceAccessor);
             OnResolve(serviceType, serviceProviderEngineScope);
             DependencyInjectionEventSource.Log.ServiceResolved(serviceType);
-            return realizedService.Invoke(serviceProviderEngineScope);
+            var result = realizedService.Invoke(serviceProviderEngineScope);
+            System.Diagnostics.Debug.Assert(result is null || CallSiteFactory.IsService(serviceType));
+            return result;
         }
 
         private void ValidateService(ServiceDescriptor descriptor)

src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.External.Tests/Autofac.cs

@@ -9,6 +9,8 @@ namespace Microsoft.Extensions.DependencyInjection.Specification
 {
     public class AutofacDependencyInjectionSpecificationTests : DependencyInjectionSpecificationTests
     {
+        public override bool SupportsIServiceProviderIsService => false;
+
         protected override IServiceProvider CreateServiceProvider(IServiceCollection serviceCollection)
         {
             var builder = new ContainerBuilder();

src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.External.Tests/DryIoc.cs

@@ -7,8 +7,10 @@
 
 namespace Microsoft.Extensions.DependencyInjection.Specification
 {
-    public class DryIocDependencyInjectionSpecificationTests: DependencyInjectionSpecificationTests
+    public class DryIocDependencyInjectionSpecificationTests : DependencyInjectionSpecificationTests
     {
+        public override bool SupportsIServiceProviderIsService => false;
+
         protected override IServiceProvider CreateServiceProvider(IServiceCollection serviceCollection)
         {
             return new Container()

src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.External.Tests/Grace.cs

@@ -9,6 +9,8 @@ namespace Microsoft.Extensions.DependencyInjection.Specification
 {
     public class GraceDependencyInjectionSpecificationTests: SkippableDependencyInjectionSpecificationTests
     {
+        public override bool SupportsIServiceProviderIsService => false;
+
         public override string[] SkippedTests => new[]
         {
             "ResolvesMixedOpenClosedGenericsAsEnumerable",

src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.External.Tests/Lamar.cs

@@ -7,6 +7,8 @@ namespace Microsoft.Extensions.DependencyInjection.Specification
 {
     public class LamarDependencyInjectionSpecificationTests : SkippableDependencyInjectionSpecificationTests
     {
+        public override bool SupportsIServiceProviderIsService => false;
+
         public override string[] SkippedTests => new[]
         {
             "DisposesInReverseOrderOfCreation",

src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.External.Tests/LightInject.cs

@@ -10,6 +10,8 @@ namespace Microsoft.Extensions.DependencyInjection.Specification
 {
     public class LightInjectDependencyInjectionSpecificationTests: DependencyInjectionSpecificationTests
     {
+        public override bool SupportsIServiceProviderIsService => false;
+
         protected override IServiceProvider CreateServiceProvider(IServiceCollection serviceCollection)
         {
             var builder = new ContainerBuilder();