Use attributes for application part discovery (#10271)

* Use attributes for application part discovery

Fixes #4332

Author: pranavkm

eng/SharedFramework.External.props

@@ -56,9 +56,6 @@
     <ExternalAspNetCoreAppReference Include="System.Security.Cryptography.Xml"                             Version="$(SystemSecurityCryptographyXmlPackageVersion)" />
     <ExternalAspNetCoreAppReference Include="System.Threading.Channels"                                    Version="$(SystemThreadingChannelsPackageVersion)" />
 
-    <!-- Dependencies from dotnet/core-setup -->
-    <ExternalAspNetCoreAppReference Include="Microsoft.Extensions.DependencyModel"                         Version="$(MicrosoftExtensionsDependencyModelPackageVersion)" />
-
     <!--
       Transitive dependencies of other assemblies in the shared framework. These are listed separately and should not be included directly
       when setting `<Reference>`. These are listed for the purpose of tests and servicing builds only.

src/Mvc/Mvc.Core/ref/Microsoft.AspNetCore.Mvc.Core.csproj

@@ -15,7 +15,6 @@
     <Reference Include="Microsoft.AspNetCore.Routing.Abstractions"  />
     <Reference Include="Microsoft.AspNetCore.Routing"  />
     <Reference Include="Microsoft.Extensions.DependencyInjection"  />
-    <Reference Include="Microsoft.Extensions.DependencyModel"  />
     <Reference Include="Microsoft.Extensions.FileProviders.Abstractions"  />
     <Reference Include="Microsoft.Extensions.Logging.Abstractions"  />
     <Reference Include="Microsoft.Extensions.ParameterDefaultValue.Sources"  />

src/Mvc/Mvc.Core/ref/Microsoft.AspNetCore.Mvc.Core.netcoreapp3.0.cs

@@ -1547,6 +1547,12 @@ public abstract partial class ApplicationPart
         protected ApplicationPart() { }
         public abstract string Name { get; }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Assembly, AllowMultiple=true)]
+    public sealed partial class ApplicationPartAttribute : System.Attribute
+    {
+        public ApplicationPartAttribute(string assemblyName) { }
+        public string AssemblyName { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
+    }
     public abstract partial class ApplicationPartFactory
     {
         protected ApplicationPartFactory() { }
@@ -1560,13 +1566,12 @@ public ApplicationPartManager() { }
         public System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.ApplicationParts.IApplicationFeatureProvider> FeatureProviders { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
         public void PopulateFeature<TFeature>(TFeature feature) { }
     }
-    public partial class AssemblyPart : Microsoft.AspNetCore.Mvc.ApplicationParts.ApplicationPart, Microsoft.AspNetCore.Mvc.ApplicationParts.IApplicationPartTypeProvider, Microsoft.AspNetCore.Mvc.ApplicationParts.ICompilationReferencesProvider
+    public partial class AssemblyPart : Microsoft.AspNetCore.Mvc.ApplicationParts.ApplicationPart, Microsoft.AspNetCore.Mvc.ApplicationParts.IApplicationPartTypeProvider
     {
         public AssemblyPart(System.Reflection.Assembly assembly) { }
         public System.Reflection.Assembly Assembly { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
         public override string Name { get { throw null; } }
         public System.Collections.Generic.IEnumerable<System.Reflection.TypeInfo> Types { get { throw null; } }
-        public System.Collections.Generic.IEnumerable<string> GetReferencePaths() { throw null; }
     }
     public partial class DefaultApplicationPartFactory : Microsoft.AspNetCore.Mvc.ApplicationParts.ApplicationPartFactory
     {

src/Mvc/Mvc.Core/src/ApplicationParts/ApplicationAssembliesProvider.cs

@@ -0,0 +1,33 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.AspNetCore.Mvc.ApplicationParts
+{
+    /// <summary>
+    /// Specifies an assembly to be added as an <see cref="ApplicationPart" />.
+    /// <para>
+    /// In the ordinary case, MVC will generate <see cref="ApplicationPartAttribute" />
+    /// instances on the entry assembly for each dependency that references MVC.
+    /// Each of these assemblies is treated as an <see cref="ApplicationPart" />.
+    /// </para>
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
+    public sealed class ApplicationPartAttribute : Attribute
+    {
+        /// <summary>
+        /// Initializes a new instance of <see cref="ApplicationPartAttribute" />.
+        /// </summary>
+        /// <param name="assemblyName">The assembly name.</param>
+        public ApplicationPartAttribute(string assemblyName)
+        {
+            AssemblyName = assemblyName ?? throw new ArgumentNullException(nameof(assemblyName));
+        }
+
+        /// <summary>
+        /// Gets the assembly name.
+        /// </summary>
+        public string AssemblyName { get; }
+    }
+}