Make RazorViewEngineOptions.FileProvider a list instead of a single item

Fixes #3806

samples/EmbeddedViewSample.Web/Startup.cs

@@ -20,10 +20,12 @@ namespace EmbeddedViewSample.Web
 
             services.Configure<RazorViewEngineOptions>(options =>
             {
+                options.FileProviders.Clear();
+
                 // Base namespace matches the resources added to the assembly from the EmbeddedResources folder.
-                options.FileProvider = new EmbeddedFileProvider(
+                options.FileProviders.Add(new EmbeddedFileProvider(
                     GetType().GetTypeInfo().Assembly,
-                    baseNamespace: "EmbeddedViewSample.Web.EmbeddedResources");
+                    baseNamespace: "EmbeddedViewSample.Web.EmbeddedResources"));
             });
         }
 

src/Microsoft.AspNet.Mvc.Razor/Compilation/DefaultCompilerCacheProvider.cs

@@ -13,11 +13,10 @@ namespace Microsoft.AspNet.Mvc.Razor.Compilation
         /// <summary>
         /// Initializes a new instance of <see cref="DefaultCompilerCacheProvider"/>.
         /// </summary>
-        /// <param name="optionsAccessor">An accessor to the <see cref="RazorViewEngineOptions"/>.</param>
+        /// <param name="fileProviderAccessor">The <see cref="IRazorViewEngineFileProviderAccessor"/>.</param>
-        public DefaultCompilerCacheProvider(IOptions<RazorViewEngineOptions> mvcViewOptions)
+        public DefaultCompilerCacheProvider(IRazorViewEngineFileProviderAccessor fileProviderAccessor)
         {
-            var fileProvider = mvcViewOptions.Value.FileProvider;
+            Cache = new CompilerCache(fileProviderAccessor.FileProvider);
-            Cache = new CompilerCache(fileProvider);
         }
 
         /// <inheritdoc />

src/Microsoft.AspNet.Mvc.Razor/Compilation/PrecompiledViewsCompilerCacheProvider.cs

@@ -33,16 +33,16 @@ namespace Microsoft.AspNet.Mvc.Razor.Compilation
         /// <summary>
         /// Initializes a new instance of <see cref="DefaultCompilerCacheProvider"/>.
         /// </summary>
-        /// <param name="loaderContextAccessor">The <see cref="IAssemblyLoadContextAccessor"/>.</param>
+        /// <param name="loadContextAccessor">The <see cref="IAssemblyLoadContextAccessor"/>.</param>
-        /// <param name="optionsAccessor">An accessor to the <see cref="RazorViewEngineOptions"/>.</param>
+        /// <param name="fileProviderAccessor">The <see cref="IRazorViewEngineFileProviderAccessor"/>.</param>
         /// <param name="assemblies"><see cref="Assembly"/> instances to scan for precompiled views.</param>
         public PrecompiledViewsCompilerCacheProvider(
             IAssemblyLoadContextAccessor loadContextAccessor,
-            IOptions<RazorViewEngineOptions> mvcViewOptions,
+            IRazorViewEngineFileProviderAccessor fileProviderAccessor,
             IEnumerable<Assembly> assemblies)
         {
             _loadContextAccessor = loadContextAccessor;
-            _fileProvider = mvcViewOptions.Value.FileProvider;
+            _fileProvider = fileProviderAccessor.FileProvider;
             _createCache = CreateCache;
             _assemblies = assemblies.ToArray();
         }

src/Microsoft.AspNet.Mvc.Razor/Compilation/RazorCompilationService.cs

@@ -27,17 +27,15 @@ namespace Microsoft.AspNet.Mvc.Razor.Compilation
         /// </summary>
         /// <param name="compilationService">The <see cref="ICompilationService"/> to compile generated code.</param>
         /// <param name="razorHost">The <see cref="IMvcRazorHost"/> to generate code from Razor files.</param>
-        /// <param name="viewEngineOptions">
+        /// <param name="fileProviderAccessor">The <see cref="IRazorViewEngineFileProviderAccessor"/>.</param>
-        /// The <see cref="IFileProvider"/> to read Razor files referenced in error messages.
-        /// </param>
         public RazorCompilationService(
             ICompilationService compilationService,
             IMvcRazorHost razorHost,
-            IOptions<RazorViewEngineOptions> viewEngineOptions)
+            IRazorViewEngineFileProviderAccessor fileProviderAccessor)
         {
             _compilationService = compilationService;
             _razorHost = razorHost;
-            _fileProvider = viewEngineOptions.Value.FileProvider;
+            _fileProvider = fileProviderAccessor.FileProvider;
         }
 
         /// <inheritdoc />
@@ -105,9 +103,10 @@ namespace Microsoft.AspNet.Mvc.Razor.Compilation
 
         private DiagnosticMessage CreateDiagnosticMessage(RazorError error, string filePath)
         {
+            var location = error.Location;
             return new DiagnosticMessage(
                 message: error.Message,
-                formattedMessage: $"{error} ({error.Location.LineIndex},{error.Location.CharacterIndex}) {error.Message}",
+                formattedMessage: $"{error} ({location.LineIndex},{location.CharacterIndex}) {error.Message}",
                 filePath: filePath,
                 startLine: error.Location.LineIndex + 1,
                 startColumn: error.Location.CharacterIndex,

src/Microsoft.AspNet.Mvc.Razor/Compilation/RoslynCompilationService.cs

@@ -51,21 +51,21 @@ namespace Microsoft.AspNet.Mvc.Razor.Compilation
         /// Initalizes a new instance of the <see cref="RoslynCompilationService"/> class.
         /// </summary>
         /// <param name="environment">The environment for the executing application.</param>
-        /// <param name="loaderAccessor">
-        /// The accessor for the <see cref="IAssemblyLoadContext"/> used to load compiled assemblies.
-        /// </param>
         /// <param name="libraryExporter">The library manager that provides export and reference information.</param>
         /// <param name="host">The <see cref="IMvcRazorHost"/> that was used to generate the code.</param>
+        /// <param name="optionsAccessor">Accessor to <see cref="RazorViewEngineOptions"/>.</param>
+        /// <param name="fileProviderAccessor">The <see cref="IRazorViewEngineFileProviderAccessor"/>.</param>
         public RoslynCompilationService(
             IApplicationEnvironment environment,
             Extensions.CompilationAbstractions.ILibraryExporter libraryExporter,
             IMvcRazorHost host,
-            IOptions<RazorViewEngineOptions> optionsAccessor)
+            IOptions<RazorViewEngineOptions> optionsAccessor,
+            IRazorViewEngineFileProviderAccessor fileProviderAccessor)
         {
             _environment = environment;
             _libraryExporter = libraryExporter;
             _applicationReferences = new Lazy<List<MetadataReference>>(GetApplicationReferences);
-            _fileProvider = optionsAccessor.Value.FileProvider;
+            _fileProvider = fileProviderAccessor.FileProvider;
             _classPrefix = host.MainClassNamePrefix;
             _compilationCallback = optionsAccessor.Value.CompilationCallback;
             _parseOptions = optionsAccessor.Value.ParseOptions;

src/Microsoft.AspNet.Mvc.Razor/DefaultRazorViewEngineFileProviderAccessor.cs

@@ -0,0 +1,36 @@
+// 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 Microsoft.AspNet.FileProviders;
+using Microsoft.Extensions.Options;
+
+namespace Microsoft.AspNet.Mvc.Razor
+{
+    /// <summary>
+    /// Default implementation of <see cref="IRazorViewEngineFileProviderAccessor"/>.
+    /// </summary>
+    public class DefaultRazorViewEngineFileProviderAccessor : IRazorViewEngineFileProviderAccessor
+    {
+        /// <summary>
+        /// Initializes a new instance of <see cref="DefaultRazorViewEngineFileProviderAccessor"/>.
+        /// </summary>
+        /// <param name="optionsAccessor">Accessor to <see cref="RazorViewEngineOptions"/>.</param>
+        public DefaultRazorViewEngineFileProviderAccessor(IOptions<RazorViewEngineOptions> optionsAccessor)
+        {
+            var fileProviders = optionsAccessor.Value.FileProviders;
+            if (fileProviders.Count == 1)
+            {
+                FileProvider = fileProviders[0];
+            }
+            else
+            {
+                FileProvider = new CompositeFileProvider(fileProviders);
+            }
+        }
+
+        /// <summary>
+        /// Gets the <see cref="IFileProvider"/> used to look up Razor files.
+        /// </summary>
+        public IFileProvider FileProvider { get; }
+    }
+}

src/Microsoft.AspNet.Mvc.Razor/DependencyInjection/MvcRazorMvcCoreBuilderExtensions.cs

@@ -14,7 +14,6 @@ using Microsoft.AspNet.Razor.TagHelpers;
 using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.CompilationAbstractions;
 using Microsoft.Extensions.DependencyInjection.Extensions;
-using Microsoft.Extensions.MemoryPool;
 using Microsoft.Extensions.Options;
 using Microsoft.Extensions.PlatformAbstractions;
 
@@ -130,12 +129,14 @@ namespace Microsoft.Extensions.DependencyInjection
             services.TryAddEnumerable(
                 ServiceDescriptor.Transient<IConfigureOptions<RazorViewEngineOptions>, RazorViewEngineOptionsSetup>());
 
+            services.TryAddSingleton<IRazorViewEngineFileProviderAccessor, DefaultRazorViewEngineFileProviderAccessor>();
+
             services.TryAddSingleton<IRazorViewEngine, RazorViewEngine>();
 
             services.TryAdd(ServiceDescriptor.Singleton<IChunkTreeCache>(serviceProvider =>
             {
-                var cachedFileProvider = serviceProvider.GetRequiredService<IOptions<RazorViewEngineOptions>>();
+                var accessor = serviceProvider.GetRequiredService<IRazorViewEngineFileProviderAccessor>();
-                return new DefaultChunkTreeCache(cachedFileProvider.Value.FileProvider);
+                return new DefaultChunkTreeCache(accessor.FileProvider);
             }));
 
             // Caches compilation artifacts across the lifetime of the application.

src/Microsoft.AspNet.Mvc.Razor/IRazorViewEngineFileProviderAccessor.cs

@@ -0,0 +1,18 @@
+// 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 Microsoft.AspNet.FileProviders;
+
+namespace Microsoft.AspNet.Mvc.Razor
+{
+    /// <summary>
+    /// Accessor to the <see cref="IFileProvider"/> used by <see cref="RazorViewEngine"/>.
+    /// </summary>
+    public interface IRazorViewEngineFileProviderAccessor
+    {
+        /// <summary>
+        /// Gets the <see cref="IFileProvider"/> used to look up Razor files.
+        /// </summary>
+        IFileProvider FileProvider { get; }
+    }
+}

src/Microsoft.AspNet.Mvc.Razor/RazorViewEngineOptions.cs

@@ -14,12 +14,9 @@ namespace Microsoft.AspNet.Mvc.Razor
     /// </summary>
     public class RazorViewEngineOptions
     {
-        private IFileProvider _fileProvider;
-
         private CSharpParseOptions _parseOptions = new CSharpParseOptions(LanguageVersion.CSharp6);
-
+        private CSharpCompilationOptions _compilationOptions =
-        private CSharpCompilationOptions _compilationOptions = new CSharpCompilationOptions(CodeAnalysis.OutputKind.DynamicallyLinkedLibrary);
+            new CSharpCompilationOptions(CodeAnalysis.OutputKind.DynamicallyLinkedLibrary);
-
         private Action<RoslynCompilationContext> _compilationCallback = c => { };
 
         /// <summary>
@@ -29,33 +26,22 @@ namespace Microsoft.AspNet.Mvc.Razor
             = new List<IViewLocationExpander>();
 
         /// <summary>
-        /// Gets or sets the <see cref="IFileProvider" /> used by <see cref="RazorViewEngine"/> to locate Razor files on
+        /// Gets the sequence of <see cref="IFileProvider" /> instances used by <see cref="RazorViewEngine"/> to
-        /// disk.
+        /// locate Razor files.
         /// </summary>
         /// <remarks>
-        /// At startup, this is initialized to an instance of <see cref="PhysicalFileProvider"/> that is rooted at the
+        /// At startup, this is initialized to include an instance of <see cref="PhysicalFileProvider"/> that is
-        /// application root.
+        /// rooted at the application root.
         /// </remarks>
-        public IFileProvider FileProvider
+        public IList<IFileProvider> FileProviders { get; } = new List<IFileProvider>();
-        {
-            get { return _fileProvider; }
-
-            set
-            {
-                if (value == null)
-                {
-                    throw new ArgumentNullException(nameof(value));
-                }
-
-                _fileProvider = value;
-            }
-        }
 
         /// <summary>
         /// Gets or sets the callback that is used to customize Razor compilation
         /// to change compilation settings you can update <see cref="RoslynCompilationContext.Compilation"/> property.
-        /// Customizations made here would not reflect in tooling (Intellisense).
         /// </summary>
+        /// <remarks>
+        /// Customizations made here would not reflect in tooling (Intellisense).
+        /// </remarks>
         public Action<RoslynCompilationContext> CompilationCallback
         {
             get { return _compilationCallback; }
@@ -65,6 +51,7 @@ namespace Microsoft.AspNet.Mvc.Razor
                 {
                     throw new ArgumentNullException(nameof(value));
                 }
+
                 _compilationCallback = value;
             }
         }
@@ -81,6 +68,7 @@ namespace Microsoft.AspNet.Mvc.Razor
                 {
                     throw new ArgumentNullException(nameof(value));
                 }
+
                 _parseOptions = value;
             }
         }
@@ -97,9 +85,9 @@ namespace Microsoft.AspNet.Mvc.Razor
                 {
                     throw new ArgumentNullException(nameof(value));
                 }
+
                 _compilationOptions = value;
             }
         }
-
     }
 }

src/Microsoft.AspNet.Mvc.Razor/RazorViewEngineOptionsSetup.cs

@@ -31,7 +31,7 @@ namespace Microsoft.AspNet.Mvc
             IApplicationEnvironment applicationEnvironment,
             IHostingEnvironment hostingEnvironment)
         {
-            razorOptions.FileProvider = new PhysicalFileProvider(applicationEnvironment.ApplicationBasePath);
+            razorOptions.FileProviders.Add(new PhysicalFileProvider(applicationEnvironment.ApplicationBasePath));
 
             var parseOptions = new CSharpParseOptions(LanguageVersion.CSharp6);
             var compilationOptions = new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary);

src/Microsoft.AspNet.Mvc.Razor/project.json

@@ -10,6 +10,7 @@
     "keyFile": "../../tools/Key.snk"
   },
   "dependencies": {
+    "Microsoft.AspNet.FileProviders.Composite": "1.0.0-*",
     "Microsoft.AspNet.Mvc.Razor.Host": "6.0.0-*",
     "Microsoft.AspNet.Mvc.ViewFeatures": "6.0.0-*",
     "Microsoft.AspNet.Razor.Runtime.Precompilation": "4.0.0-*",
@@ -26,8 +27,7 @@
       "type": "build"
     },
     "Microsoft.Dnx.Compilation.CSharp.Common": "1.0.0-*",
-    "Microsoft.Dnx.Compilation.CSharp.Abstractions": "1.0.0-*",
+    "Microsoft.Dnx.Compilation.CSharp.Abstractions": "1.0.0-*"
-    "Microsoft.Extensions.MemoryPool": "1.0.0-*"
   },
   "frameworks": {
     "net451": {

test/Microsoft.AspNet.Mvc.Razor.Test/Compilation/RazorCompilationServiceTest.cs

@@ -38,7 +38,7 @@ namespace Microsoft.AspNet.Mvc.Razor.Compilation
             compiler.Setup(c => c.Compile(relativeFileInfo, It.IsAny<string>()))
                     .Returns(new CompilationResult(typeof(RazorCompilationServiceTest)));
 
-            var razorService = new RazorCompilationService(compiler.Object, host.Object, GetOptions());
+            var razorService = new RazorCompilationService(compiler.Object, host.Object, GetFileProviderAccessor());
 
             // Act
             razorService.Compile(relativeFileInfo);
@@ -70,7 +70,7 @@ namespace Microsoft.AspNet.Mvc.Razor.Compilation
 
             var compiler = new Mock<ICompilationService>(MockBehavior.Strict);
             var relativeFileInfo = new RelativeFileInfo(fileInfo.Object, @"Views\index\home.cshtml");
-            var razorService = new RazorCompilationService(compiler.Object, host.Object, GetOptions());
+            var razorService = new RazorCompilationService(compiler.Object, host.Object, GetFileProviderAccessor());
 
             // Act
             var result = razorService.Compile(relativeFileInfo);
@@ -111,7 +111,7 @@ namespace Microsoft.AspNet.Mvc.Razor.Compilation
             compiler.Setup(c => c.Compile(relativeFileInfo, code))
                     .Returns(compilationResult)
                     .Verifiable();
-            var razorService = new RazorCompilationService(compiler.Object, host.Object, GetOptions());
+            var razorService = new RazorCompilationService(compiler.Object, host.Object, GetFileProviderAccessor());
 
             // Act
             var result = razorService.Compile(relativeFileInfo);
@@ -136,7 +136,7 @@ namespace Microsoft.AspNet.Mvc.Razor.Compilation
             var razorService = new RazorCompilationService(
                 Mock.Of<ICompilationService>(),
                 Mock.Of<IMvcRazorHost>(),
-                GetOptions(fileProvider));
+                GetFileProviderAccessor(fileProvider));
             var errors = new[]
             {
                 new RazorError("message-1", new SourceLocation(1, 2, 17), length: 1),
@@ -211,15 +211,11 @@ namespace Microsoft.AspNet.Mvc.Razor.Compilation
                     new ChunkTree());
         }
 
-        private static IOptions<RazorViewEngineOptions> GetOptions(IFileProvider fileProvider = null)
+        private static IRazorViewEngineFileProviderAccessor GetFileProviderAccessor(IFileProvider fileProvider = null)
         {
-            var razorViewEngineOptions = new RazorViewEngineOptions
+            var options = new Mock<IRazorViewEngineFileProviderAccessor>();
-            {
+            options.SetupGet(o => o.FileProvider)
-                FileProvider = fileProvider ?? new TestFileProvider()
+                .Returns(fileProvider ?? new TestFileProvider());
-            };
-            var options = new Mock<IOptions<RazorViewEngineOptions>>();
-            options.SetupGet(o => o.Value)
-                .Returns(razorViewEngineOptions);
 
             return options.Object;
         }

test/Microsoft.AspNet.Mvc.Razor.Test/Compilation/RoslynCompilationServiceTest.cs

@@ -2,11 +2,9 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Runtime.Versioning;
 using Microsoft.AspNet.FileProviders;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Text;
-using Microsoft.Dnx.Runtime;
 using Microsoft.Extensions.CompilationAbstractions;
 using Microsoft.Extensions.Options;
 using Microsoft.Extensions.PlatformAbstractions;
@@ -35,7 +33,8 @@ public class MyTestType  {}";
                 applicationEnvironment,
                 libraryExporter,
                 mvcRazorHost.Object,
-                GetOptions());
+                GetOptions(),
+                GetFileProviderAccessor());
             var relativeFileInfo = new RelativeFileInfo(
                 new TestFileInfo { PhysicalPath = "SomePath" },
                 "some-relative-path");
@@ -66,7 +65,8 @@ this should fail";
                 applicationEnvironment,
                 libraryExporter,
                 mvcRazorHost,
-                GetOptions(fileProvider));
+                GetOptions(),
+                GetFileProviderAccessor(fileProvider));
             var relativeFileInfo = new RelativeFileInfo(fileInfo, "some-relative-path");
 
             // Act
@@ -94,7 +94,8 @@ this should fail";
                 applicationEnvironment,
                 libraryExporter,
                 mvcRazorHost,
-                GetOptions());
+                GetOptions(),
+                GetFileProviderAccessor());
             var relativeFileInfo = new RelativeFileInfo(
                 new TestFileInfo { Content = fileContent },
                 "some-relative-path");
@@ -125,7 +126,7 @@ this should fail";
 
             var mockFileInfo = new Mock<IFileInfo>();
             mockFileInfo.Setup(f => f.CreateReadStream())
-                        .Throws(new Exception());
+                .Throws(new Exception());
             var fileProvider = new TestFileProvider();
             fileProvider.AddFile(path, mockFileInfo.Object);
 
@@ -133,7 +134,8 @@ this should fail";
                 applicationEnvironment,
                 libraryExporter,
                 mvcRazorHost,
-                GetOptions(fileProvider));
+                GetOptions(),
+                GetFileProviderAccessor(fileProvider));
 
             var relativeFileInfo = new RelativeFileInfo(mockFileInfo.Object, path);
 
@@ -163,7 +165,7 @@ public class MyNonCustomDefinedClass {}
             var libraryExporter = CompilationServices.Default.LibraryExporter;
             var mvcRazorHost = new Mock<IMvcRazorHost>();
             mvcRazorHost.SetupGet(m => m.MainClassNamePrefix)
-                        .Returns("My");
+                .Returns("My");
 
             var options = GetOptions();
             options.Value.ParseOptions = options.Value.ParseOptions.WithPreprocessorSymbols("MY_CUSTOM_DEFINE");
@@ -172,7 +174,8 @@ public class MyNonCustomDefinedClass {}
                 applicationEnvironment,
                 libraryExporter,
                 mvcRazorHost.Object,
-                options);
+                options,
+                GetFileProviderAccessor());
             var relativeFileInfo = new RelativeFileInfo(
                 new TestFileInfo { PhysicalPath = "SomePath" },
                 "some-relative-path");
@@ -202,7 +205,8 @@ public class NotRazorPrefixType {}";
                 applicationEnvironment,
                 libraryExporter,
                 mvcRazorHost.Object,
-                GetOptions());
+                GetOptions(),
+                GetFileProviderAccessor());
 
             var relativeFileInfo = new RelativeFileInfo(
                 new TestFileInfo { PhysicalPath = "SomePath" },
@@ -224,17 +228,17 @@ public class NotRazorPrefixType {}";
             var generatedCodeFileName = "Generated Code";
             var fileProvider = new TestFileProvider();
             fileProvider.AddFile(viewPath, "view-content");
-            var options = new Mock<IOptions<RazorViewEngineOptions>>();
+            var options = new RazorViewEngineOptions();
-            options.SetupGet(o => o.Value)
+            options.FileProviders.Add(fileProvider);
-                .Returns(new RazorViewEngineOptions
+            var optionsAccessor = new Mock<IOptions<RazorViewEngineOptions>>();
-                {
+            optionsAccessor.SetupGet(o => o.Value)
-                    FileProvider = fileProvider
+                .Returns(options);
-                });
             var compilationService = new RoslynCompilationService(
                 PlatformServices.Default.Application,
                 CompilationServices.Default.LibraryExporter,
                 Mock.Of<IMvcRazorHost>(),
-                options.Object);
+                optionsAccessor.Object,
+                GetFileProviderAccessor(fileProvider));
 
             var assemblyName = "random-assembly-name";
 
@@ -325,7 +329,8 @@ public class NotRazorPrefixType {}";
                 applicationEnvironment,
                 libraryExporter,
                 mvcRazorHost.Object,
-                GetOptions(callback: c => usedCompilation = c));
+                GetOptions(callback: c => usedCompilation = c),
+                GetFileProviderAccessor());
 
             var relativeFileInfo = new RelativeFileInfo(
                 new TestFileInfo { PhysicalPath = "SomePath" },
@@ -350,13 +355,11 @@ public class NotRazorPrefixType {}";
                 isEnabledByDefault: true);
         }
 
-        private static IOptions<RazorViewEngineOptions> GetOptions(IFileProvider fileProvider = null,
+        private static IOptions<RazorViewEngineOptions> GetOptions(Action<RoslynCompilationContext> callback = null)
-            Action<RoslynCompilationContext> callback = null)
         {
             var razorViewEngineOptions = new RazorViewEngineOptions
             {
-                FileProvider = fileProvider ?? new TestFileProvider(),
+                CompilationCallback = callback ?? (c => { }),
-                CompilationCallback = callback ?? (c => { })
             };
             var options = new Mock<IOptions<RazorViewEngineOptions>>();
             options
@@ -365,5 +368,14 @@ public class NotRazorPrefixType {}";
 
             return options.Object;
         }
+
+        private IRazorViewEngineFileProviderAccessor GetFileProviderAccessor(IFileProvider fileProvider = null)
+        {
+            var options = new Mock<IRazorViewEngineFileProviderAccessor>();
+            options.SetupGet(o => o.FileProvider)
+                .Returns(fileProvider ?? new TestFileProvider());
+
+            return options.Object;
+        }
     }
 }

test/Microsoft.AspNet.Mvc.Razor.Test/DefaultRazorViewEngineFileProviderAccessorTest.cs

@@ -0,0 +1,67 @@
+// 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 Microsoft.AspNet.FileProviders;
+using Microsoft.AspNet.Mvc.Internal;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+using Moq;
+using Xunit;
+
+namespace Microsoft.AspNet.Mvc.Razor
+{
+    public class DefaultRazorViewEngineFileProviderAccessorTest
+    {
+        [Fact]
+        public void FileProvider_ReturnsInstanceIfExactlyOneFileProviderIsSpecified()
+        {
+            // Arrange
+            var fileProvider = new TestFileProvider();
+            var options = new RazorViewEngineOptions();
+            options.FileProviders.Add(fileProvider);
+            var optionsAccessor = new Mock<IOptions<RazorViewEngineOptions>>();
+            optionsAccessor.SetupGet(o => o.Value).Returns(options);
+            var fileProviderAccessor = new DefaultRazorViewEngineFileProviderAccessor(optionsAccessor.Object);
+
+            // Act
+            var actual = fileProviderAccessor.FileProvider;
+
+            // Assert
+            Assert.Same(fileProvider, actual);
+        }
+
+        [Fact]
+        public void FileProvider_ReturnsCompositeFileProviderIfNoInstancesAreRegistered()
+        {
+            // Arrange
+            var options = new RazorViewEngineOptions();
+            var optionsAccessor = new Mock<IOptions<RazorViewEngineOptions>>();
+            optionsAccessor.SetupGet(o => o.Value).Returns(options);
+            var fileProviderAccessor = new DefaultRazorViewEngineFileProviderAccessor(optionsAccessor.Object);
+
+            // Act
+            var actual = fileProviderAccessor.FileProvider;
+
+            // Assert
+            Assert.IsType<CompositeFileProvider>(actual);
+        }
+
+        [Fact]
+        public void FileProvider_ReturnsCompositeFileProviderIfMoreThanOneInstanceIsRegistered()
+        {
+            // Arrange
+            var options = new RazorViewEngineOptions();
+            options.FileProviders.Add(new TestFileProvider());
+            options.FileProviders.Add(new TestFileProvider());
+            var optionsAccessor = new Mock<IOptions<RazorViewEngineOptions>>();
+            optionsAccessor.SetupGet(o => o.Value).Returns(options);
+            var fileProviderAccessor = new DefaultRazorViewEngineFileProviderAccessor(optionsAccessor.Object);
+
+            // Act
+            var actual = fileProviderAccessor.FileProvider;
+
+            // Assert
+            Assert.IsType<CompositeFileProvider>(actual);
+        }
+    }
+}

test/Microsoft.AspNet.Mvc.Razor.Test/RazorViewEngineOptionsTest.cs

@@ -1,7 +1,6 @@
 // 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 Microsoft.AspNet.Mvc.Internal;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Options;
@@ -12,18 +11,7 @@ namespace Microsoft.AspNet.Mvc.Razor
     public class RazorViewEngineOptionsTest
     {
         [Fact]
-        public void FileProviderThrows_IfNullIsAssigned()
+        public void AddRazorOptions_ConfiguresOptionsAsExpected()
-        {
-            // Arrange
-            var options = new RazorViewEngineOptions();
-
-            // Act and Assert
-            var ex = Assert.Throws<ArgumentNullException>(() => options.FileProvider = null);
-            Assert.Equal("value", ex.ParamName);
-        }
-
-        [Fact]
-        public void AddRazorOptions_ConfiguresOptionsProperly()
         {
             // Arrange
             var services = new ServiceCollection().AddOptions();
@@ -33,13 +21,13 @@ namespace Microsoft.AspNet.Mvc.Razor
             var builder = new MvcBuilder(services);
             builder.AddRazorOptions(options =>
             {
-                options.FileProvider = fileProvider;
+                options.FileProviders.Add(fileProvider);
             });
             var serviceProvider = services.BuildServiceProvider();
 
             // Assert
             var accessor = serviceProvider.GetRequiredService<IOptions<RazorViewEngineOptions>>();
-            Assert.Same(fileProvider, accessor.Value.FileProvider);
+            Assert.Same(fileProvider, accessor.Value.FileProviders[0]);
         }
     }
 }

test/Microsoft.AspNet.Mvc.Test/RazorViewEngineOptionsSetupTest.cs

@@ -21,18 +21,18 @@ namespace Microsoft.AspNet.Mvc
             var options = new RazorViewEngineOptions();
             var appEnv = new Mock<IApplicationEnvironment>();
             appEnv.SetupGet(e => e.ApplicationBasePath)
-                  .Returns(Directory.GetCurrentDirectory());
+                .Returns(Directory.GetCurrentDirectory());
             var hostingEnv = new Mock<IHostingEnvironment>();
             hostingEnv.SetupGet(e => e.EnvironmentName)
-                  .Returns("Development");
+                .Returns("Development");
             var optionsSetup = new RazorViewEngineOptionsSetup(appEnv.Object, hostingEnv.Object);
 
             // Act
             optionsSetup.Configure(options);
 
             // Assert
-            Assert.NotNull(options.FileProvider);
+            var fileProvider = Assert.Single(options.FileProviders);
-            Assert.IsType<PhysicalFileProvider>(options.FileProvider);
+            Assert.IsType<PhysicalFileProvider>(fileProvider);
         }
 
         [Theory]
@@ -62,7 +62,9 @@ namespace Microsoft.AspNet.Mvc
         [InlineData("Development", OptimizationLevel.Debug)]
         [InlineData("Staging", OptimizationLevel.Release)]
         [InlineData("Production", OptimizationLevel.Release)]
-        public void RazorViewEngineOptionsSetup_SetsOptimizationLevel(string environment, OptimizationLevel expectedOptimizationLevel)
+        public void RazorViewEngineOptionsSetup_SetsOptimizationLevel(
+            string environment,
+            OptimizationLevel expectedOptimizationLevel)
         {
             // Arrange
             var options = new RazorViewEngineOptions();

test/WebSites/RazorPageExecutionInstrumentationWebSite/TestRazorCompilationService.cs

@@ -6,7 +6,6 @@ using System.Text;
 using Microsoft.AspNet.Mvc.Razor;
 using Microsoft.AspNet.Mvc.Razor.Compilation;
 using Microsoft.AspNet.Razor.CodeGenerators;
-using Microsoft.Extensions.Options;
 
 namespace RazorPageExecutionInstrumentationWebSite
 {
@@ -15,8 +14,8 @@ namespace RazorPageExecutionInstrumentationWebSite
         public TestRazorCompilationService(
             ICompilationService compilationService,
             IMvcRazorHost razorHost,
-            IOptions<RazorViewEngineOptions> viewEngineOptions)
+            IRazorViewEngineFileProviderAccessor fileProviderAccessor)
-            : base(compilationService, razorHost, viewEngineOptions)
+            : base(compilationService, razorHost, fileProviderAccessor)
         {
         }