[Fixes issue #1528] default reference assemblies made extensible

- Made ReferenceAssemblies and GetCandidateLibraries virtual
- Added relevant tests

src/Microsoft.AspNet.Mvc.Core/DefaultAssemblyProvider.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Reflection;
 using Microsoft.Framework.Runtime;
@@ -11,8 +12,11 @@ namespace Microsoft.AspNet.Mvc
 {
     public class DefaultAssemblyProvider : IAssemblyProvider
     {
-        // List of Mvc assemblies that we'll use as roots for controller discovery.
-        private static readonly HashSet<string> _mvcAssemblyList = new HashSet<string>(StringComparer.Ordinal)
+        /// <summary>
+        /// Gets the set of assembly names that are used as root for discovery of 
+        /// MVC controllers, view components and views.
+        /// </summary>
+        protected virtual HashSet<string> ReferenceAssemblies { get; } = new HashSet<string>(StringComparer.Ordinal)
         {
             "Microsoft.AspNet.Mvc",
             "Microsoft.AspNet.Mvc.Core",
@@ -29,6 +33,7 @@ namespace Microsoft.AspNet.Mvc
             _libraryManager = libraryManager;
         }
 
+        /// <inheritdoc />
         public IEnumerable<Assembly> CandidateAssemblies
         {
             get
@@ -37,14 +42,24 @@ namespace Microsoft.AspNet.Mvc
             }
         }
 
-        internal IEnumerable<ILibraryInformation> GetCandidateLibraries()
+        /// <summary>
+        /// Returns a list of libraries that references the assemblies in <see cref="ReferenceAssemblies"/>.
+        /// By default it returns all assemblies that reference any of the primary MVC assemblies 
+        /// while ignoring MVC assemblies.
+        /// </summary>
+        /// <returns>A set of <see cref="ILibraryInformation"/>.</returns>
+        protected virtual IEnumerable<ILibraryInformation> GetCandidateLibraries()
         {
+            if (ReferenceAssemblies == null)
+            {
+                return Enumerable.Empty<ILibraryInformation>();
+            }
+
             // GetReferencingLibraries returns the transitive closure of referencing assemblies
-            // for a given assembly. In our case, we'll gather all assemblies that reference
-            // any of the primary Mvc assemblies while ignoring Mvc assemblies.
-            return _mvcAssemblyList.SelectMany(_libraryManager.GetReferencingLibraries)
-                                   .Distinct()
-                                   .Where(IsCandidateLibrary);
+            // for a given assembly.
+            return ReferenceAssemblies.SelectMany(_libraryManager.GetReferencingLibraries)
+                                      .Distinct()
+                                      .Where(IsCandidateLibrary);
         }
 
         private static Assembly Load(AssemblyName assemblyName)
@@ -52,9 +67,10 @@ namespace Microsoft.AspNet.Mvc
             return Assembly.Load(assemblyName);
         }
 
-        private static bool IsCandidateLibrary(ILibraryInformation library)
+        private bool IsCandidateLibrary(ILibraryInformation library)
         {
-            return !_mvcAssemblyList.Contains(library.Name);
+            Debug.Assert(ReferenceAssemblies != null);
+            return !ReferenceAssemblies.Contains(library.Name);
         }
     }
 }

test/Microsoft.AspNet.Mvc.Core.Test/DefaultAssemblyProviderTests.cs

@@ -1,10 +1,8 @@
 // Copyright (c) Microsoft Open Technologies, Inc. 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.Framework.Runtime;
 using Moq;
 using Xunit;
@@ -27,7 +25,7 @@ namespace Microsoft.AspNet.Mvc.Core
                         CreateLibraryInfo("SomeRandomAssembly"),
                    })
                    .Verifiable();
-            var provider = new DefaultAssemblyProvider(manager.Object);
+            var provider = new TestAssemblyProvider(manager.Object);
 
             // Act
             var candidates = provider.GetCandidateLibraries();
@@ -49,7 +47,7 @@ namespace Microsoft.AspNet.Mvc.Core
                    .Returns(new[] { CreateLibraryInfo("Bar") });
             manager.Setup(f => f.GetReferencingLibraries("Microsoft.AspNet.Mvc"))
                    .Returns(new[] { CreateLibraryInfo("Baz") });
-            var provider = new DefaultAssemblyProvider(manager.Object);
+            var provider = new TestAssemblyProvider(manager.Object);
 
             // Act
             var candidates = provider.GetCandidateLibraries();
@@ -58,11 +56,110 @@ namespace Microsoft.AspNet.Mvc.Core
             Assert.Equal(new[] { "Baz", "Foo", "Bar" }, candidates.Select(a => a.Name));
         }
 
+        [Fact]
+        public void CandidateAssemblies_ReturnsLibrariesReferencingDefaultAssemblies()
+        {
+            // Arrange
+            var defaultProvider = new TestAssemblyProvider(CreateLibraryManager());
+
+            // Act
+            var defaultProviderCandidates = defaultProvider.GetCandidateLibraries();
+
+            // Assert
+            Assert.Equal(new[] { "Baz" }, defaultProviderCandidates.Select(a => a.Name));
+        }
+
+        [Fact]
+        public void CandidateAssemblies_ReturnsLibrariesReferencingOverriddenAssemblies()
+        {
+            // Arrange
+            var overriddenProvider = new OverriddenAssemblyProvider(CreateLibraryManager());
+
+            // Act
+            var overriddenProviderCandidates = overriddenProvider.GetCandidateLibraries();
+
+            // Assert
+            Assert.Equal(new[] { "Foo", "Bar" }, overriddenProviderCandidates.Select(a => a.Name));
+        }
+
+        [Fact]
+        public void CandidateAssemblies_ReturnsEmptySequenceWhenReferenceAssembliesIsNull()
+        {
+            // Arrange
+            var nullProvider = new NullAssemblyProvider(CreateLibraryManager());
+
+            // Act
+            var nullProviderCandidates = nullProvider.GetCandidateLibraries();
+
+            // Assert
+            Assert.Empty(nullProviderCandidates.Select(a => a.Name));
+        }
+
         private static ILibraryInformation CreateLibraryInfo(string name)
         {
             var info = new Mock<ILibraryInformation>();
             info.SetupGet(b => b.Name).Returns(name);
             return info.Object;
         }
+
+        private static ILibraryManager CreateLibraryManager()
+        {
+            var manager = new Mock<ILibraryManager>();
+            manager.Setup(f => f.GetReferencingLibraries(It.IsAny<string>()))
+                  .Returns(Enumerable.Empty<ILibraryInformation>());
+            manager.Setup(f => f.GetReferencingLibraries("Microsoft.AspNet.Mvc.Core"))
+                   .Returns(new[] { CreateLibraryInfo("Baz") });
+            manager.Setup(f => f.GetReferencingLibraries("MyAssembly"))
+                   .Returns(new[] { CreateLibraryInfo("Foo") });
+            manager.Setup(f => f.GetReferencingLibraries("AnotherAssembly"))
+                   .Returns(new[] { CreateLibraryInfo("Bar") });
+            return manager.Object;
+        }
+
+        private class TestAssemblyProvider : DefaultAssemblyProvider
+        {
+            public new IEnumerable<ILibraryInformation> GetCandidateLibraries()
+            {
+                return base.GetCandidateLibraries();
+            }
+
+            public TestAssemblyProvider(ILibraryManager libraryManager) : base(libraryManager)
+            {
+            }
+        }
+
+        private class OverriddenAssemblyProvider : TestAssemblyProvider
+        {
+            protected override HashSet<string> ReferenceAssemblies
+            {
+                get
+                {
+                    return new HashSet<string>
+                    {
+                        "MyAssembly",
+                        "AnotherAssembly"
+                    };
+                }
+            }
+
+            public OverriddenAssemblyProvider(ILibraryManager libraryManager) : base(libraryManager)
+            {
+            }
+        }
+
+        private class NullAssemblyProvider : TestAssemblyProvider
+        {
+            protected override HashSet<string> ReferenceAssemblies
+            {
+                get
+                {
+                    return null;
+                }
+            }
+
+            public NullAssemblyProvider(ILibraryManager libraryManager) : base(libraryManager)
+            {
+            }
+        }
     }
 }