Revive DefaultAssemblyProviderTests

Partial fix for https://github.com/aspnet/Mvc/issues/4140

src/Microsoft.AspNetCore.Mvc.Core/Infrastructure/DefaultAssemblyProvider.cs

@@ -25,9 +25,17 @@ namespace Microsoft.AspNetCore.Mvc.Infrastructure
         /// </summary>
         /// <param name="environment">The <see cref="IApplicationEnvironment"/>.</param>
         public DefaultAssemblyProvider(IApplicationEnvironment environment)
+            : this(
+                  Assembly.Load(new AssemblyName(environment.ApplicationName)),
+                  DependencyContext.Load(Assembly.Load(new AssemblyName(environment.ApplicationName))))
         {
-            _entryAssembly = Assembly.Load(new AssemblyName(environment.ApplicationName));
-            _dependencyContext = DependencyContext.Load(_entryAssembly);
+        }
+
+        // Internal for unit testing.
+        internal DefaultAssemblyProvider(Assembly entryAssembly, DependencyContext dependencyContext)
+        {
+            _entryAssembly = entryAssembly;
+            _dependencyContext = dependencyContext;
         }
 
         /// <summary>
@@ -78,7 +86,8 @@ namespace Microsoft.AspNetCore.Mvc.Infrastructure
         /// while ignoring MVC assemblies.
         /// </summary>
         /// <returns>A set of <see cref="Library"/>.</returns>
-        protected virtual IEnumerable<RuntimeLibrary> GetCandidateLibraries()
+        // Internal for unit testing
+        protected internal virtual IEnumerable<RuntimeLibrary> GetCandidateLibraries()
         {
             if (ReferenceAssemblies == null)
             {

test/Microsoft.AspNetCore.Mvc.Core.Test/Infrastructure/DefaultAssemblyProviderTests.cs

@@ -0,0 +1,220 @@
+// 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;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyModel;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.Infrastructure
+{
+    public class DefaultAssemblyProviderTests
+    {
+        private static readonly Assembly CurrentAssembly = typeof(DefaultAssemblyProviderTests).GetTypeInfo().Assembly;
+
+        [Fact]
+        public void GetCandidateLibraries_IgnoresMvcAssemblies()
+        {
+            // Arrange
+            var expected = GetLibrary("SomeRandomAssembly", "Microsoft.AspNetCore.Mvc.Abstractions");
+            var dependencyContext = new DependencyContext(
+                target: null,
+                runtime: null,
+                compilationOptions: CompilationOptions.Default,
+                compileLibraries: new CompilationLibrary[0],
+                runtimeLibraries: new[]
+                {
+                     GetLibrary("Microsoft.AspNetCore.Mvc.Core"),
+                     GetLibrary("Microsoft.AspNetCore.Mvc"),
+                     GetLibrary("Microsoft.AspNetCore.Mvc.Abstractions"),
+                     expected,
+                });
+            var provider = new DefaultAssemblyProvider(CurrentAssembly, dependencyContext);
+
+            // Act
+            var candidates = provider.GetCandidateLibraries();
+
+            // Assert
+            Assert.Equal(new[] { expected }, candidates);
+        }
+
+        [Fact]
+        public void CandidateAssemblies_ReturnsEntryAssemblyIfDependencyContextIsNull()
+        {
+            // Arrange
+            var provider = new DefaultAssemblyProvider(CurrentAssembly, dependencyContext: null);
+
+            // Act
+            var candidates = provider.CandidateAssemblies;
+
+            // Assert
+            Assert.Equal(new[] { CurrentAssembly }, candidates);
+        }
+
+        [Fact]
+        public void GetCandidateLibraries_ReturnsLibrariesReferencingAnyMvcAssembly()
+        {
+            // Arrange
+            var dependencyContext = new DependencyContext(
+                target: null,
+                runtime: null,
+                compilationOptions: CompilationOptions.Default,
+                compileLibraries: new CompilationLibrary[0],
+                runtimeLibraries: new[]
+                {
+                     GetLibrary("Foo", "Microsoft.AspNetCore.Mvc.Core"),
+                     GetLibrary("Bar", "Microsoft.AspNetCore.Mvc"),
+                     GetLibrary("Qux", "Not.Mvc.Assembly", "Unofficial.Microsoft.AspNetCore.Mvc"),
+                     GetLibrary("Baz", "Microsoft.AspNetCore.Mvc.Abstractions"),
+                });
+            var provider = new DefaultAssemblyProvider(CurrentAssembly, dependencyContext);
+
+            // Act
+            var candidates = provider.GetCandidateLibraries();
+
+            // Assert
+            Assert.Equal(new[] { "Foo", "Bar", "Baz" }, candidates.Select(a => a.PackageName));
+        }
+
+        [Fact]
+        public void GetCandidateLibraries_ReturnsLibrariesReferencingOverriddenAssemblies()
+        {
+            // Arrange
+            var dependencyContext = new DependencyContext(
+                target: null,
+                runtime: null,
+                compilationOptions: CompilationOptions.Default,
+                compileLibraries: new CompilationLibrary[0],
+                runtimeLibraries: new[]
+                {
+                     GetLibrary("Foo", "CustomMvc.Modules"),
+                     GetLibrary("Bar", "CustomMvc.Application.Loader"),
+                     GetLibrary("Baz", "Microsoft.AspNetCore.Mvc.Abstractions"),
+                });
+            var referenceAssemblies = new HashSet<string>
+            {
+                "CustomMvc.Modules",
+                "CustomMvc.Application.Loader"
+            };
+            var assemblyProvider = new OverridenAssemblyProvider(
+                CurrentAssembly,
+                dependencyContext,
+                referenceAssemblies);
+
+            // Act
+            var candidates = assemblyProvider.GetCandidateLibraries();
+
+            // Assert
+            Assert.Equal(new[] { "Foo", "Bar" }, candidates.Select(a => a.PackageName));
+        }
+
+        [Fact]
+        public void GetCandidateLibraries_ReturnsEmptySequenceWhenReferenceAssembliesIsNull()
+        {
+            // Arrange
+            var dependencyContext = new DependencyContext(
+               target: null,
+               runtime: null,
+               compilationOptions: CompilationOptions.Default,
+               compileLibraries: new CompilationLibrary[0],
+               runtimeLibraries: new[]
+               {
+                     GetLibrary("Foo", "CustomMvc.Modules"),
+                     GetLibrary("Bar", "CustomMvc.Application.Loader"),
+                     GetLibrary("Baz", "Microsoft.AspNetCore.Mvc.Abstractions"),
+               });
+            var assemblyProvider = new OverridenAssemblyProvider(
+                CurrentAssembly,
+                dependencyContext,
+                referenceAssemblies: null);
+
+            // Act
+            var candidates = assemblyProvider.GetCandidateLibraries();
+
+            // Assert
+            Assert.Empty(candidates);
+        }
+
+        // This test verifies DefaultAssemblyProvider.ReferenceAssemblies reflects the actual loadable assemblies
+        // of the libraries that Microsoft.AspNetCore.Mvc dependes on.
+        // If we add or remove dependencies, this test should be changed together.
+        [Fact]
+        public void ReferenceAssemblies_ReturnsLoadableReferenceAssemblies()
+        {
+            // Arrange
+            var provider = new TestableAssemblyProvider(CurrentAssembly, dependencyContext: null);
+            var excludeAssemblies = new string[]
+            {
+                "Microsoft.AspNetCore.Mvc.WebApiCompatShim",
+                "Microsoft.AspNetCore.Mvc.TestCommon",
+                "Microsoft.AspNetCore.Mvc.Core.Test",
+                "Microsoft.AspNetCore.Mvc.TestDiagnosticListener.Sources",
+            };
+
+            var additionalAssemblies = new[]
+            {
+                // The following assemblies are not reachable from Microsoft.AspNetCore.Mvc
+                "Microsoft.AspNetCore.Mvc.TagHelpers",
+                "Microsoft.AspNetCore.Mvc.Formatters.Xml",
+            };
+
+            var expected = DependencyContext.Load(CurrentAssembly)
+                .RuntimeLibraries
+                .Where(r => r.PackageName.StartsWith("Microsoft.AspNetCore.Mvc", StringComparison.Ordinal) &&
+                    !excludeAssemblies.Contains(r.PackageName, StringComparer.OrdinalIgnoreCase))
+                .Select(r => r.PackageName)
+                .Concat(additionalAssemblies)
+                .Distinct()
+                .OrderBy(p => p, StringComparer.Ordinal);
+
+            // Act
+            var referenceAssemblies = provider.ReferenceAssemblies.OrderBy(p => p, StringComparer.Ordinal);
+
+            // Assert
+            Assert.Equal(expected, referenceAssemblies);
+        }
+
+        private static RuntimeLibrary GetLibrary(string name, params string[] dependencyNames)
+        {
+            var dependencies = dependencyNames?.Select(d => new Dependency(d, "42.0.0")) ?? new Dependency[0];
+
+            return new RuntimeLibrary(
+                "package",
+                name,
+                "23.0.0",
+                "hash",
+                new[] { $"{name}.dll" },
+                dependencies: dependencies.ToArray(),
+                serviceable: true);
+        }
+
+        private class OverridenAssemblyProvider : DefaultAssemblyProvider
+        {
+            public OverridenAssemblyProvider(
+                Assembly entryAssembly,
+                DependencyContext dependencyContext,
+                HashSet<string> referenceAssemblies)
+                : base(entryAssembly, dependencyContext)
+            {
+                ReferenceAssemblies = referenceAssemblies;
+            }
+
+            protected override HashSet<string> ReferenceAssemblies { get; }
+        }
+
+        private class TestableAssemblyProvider : DefaultAssemblyProvider
+        {
+            public TestableAssemblyProvider(
+                Assembly entryAssembly,
+                DependencyContext dependencyContext)
+                : base(entryAssembly, dependencyContext)
+            {
+            }
+
+            public new HashSet<string> ReferenceAssemblies => base.ReferenceAssemblies;
+        }
+    }
+}

test/Microsoft.AspNetCore.Mvc.Core.Test/project.json

@@ -1,7 +1,8 @@
 {
   "compilationOptions": {
     "warningsAsErrors": true,
-    "keyFile": "../../tools/Key.snk"
+    "keyFile": "../../tools/Key.snk",
+    "preserveCompilationContext": true
   },
   "dependencies": {
     "Microsoft.AspNetCore.Http": "1.0.0-*",