Add a feature to disable file watching in Razor pages (#8369)

* Add a feature to disable file watching in Razor pages

Fixes https://github.com/aspnet/Mvc/issues/8362

src/Microsoft.AspNetCore.Mvc.Core/Infrastructure/DefaultActionDescriptorCollectionProvider.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 System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Diagnostics;

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

@@ -159,6 +159,9 @@ namespace Microsoft.Extensions.DependencyInjection
             services.TryAddEnumerable(
                 ServiceDescriptor.Transient<IConfigureOptions<RazorViewEngineOptions>, RazorViewEngineOptionsSetup>());
 
+            services.TryAddEnumerable(
+                ServiceDescriptor.Transient<IPostConfigureOptions<RazorViewEngineOptions>, RazorViewEngineOptionsSetup>());
+
             services.TryAddSingleton<
                 IRazorViewEngineFileProviderAccessor,
                 DefaultRazorViewEngineFileProviderAccessor>();

src/Microsoft.AspNetCore.Mvc.Razor/Internal/RazorViewCompiler.cs

@@ -116,6 +116,8 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             }
         }
 
+        public bool AllowRecompilingViewsOnFileChange { get; set; }
+
         /// <inheritdoc />
         public Task<CompiledViewDescriptor> CompileAsync(string relativePath)
         {
@@ -254,16 +256,9 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 
                 // Used to validate and recompile
                 NormalizedPath = normalizedPath,
-                ExpirationTokens = new List<IChangeToken>(),
-            };
 
-            var checksums = precompiledView.Item.GetChecksumMetadata();
+                ExpirationTokens = GetExpirationTokens(precompiledView),
-            for (var i = 0; i < checksums.Count; i++)
+            };
-            {
-                // We rely on Razor to provide the right set of checksums. Trust the compiler, it has to do a good job,
-                // so it probably will.
-                item.ExpirationTokens.Add(_fileProvider.Watch(checksums[i].Identifier));
-            }
 
             // We also need to create a new descriptor, because the original one doesn't have expiration tokens on
             // it. These will be used by the view location cache, which is like an L1 cache for views (this class is
@@ -282,10 +277,13 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 
         private ViewCompilerWorkItem CreateRuntimeCompilationWorkItem(string normalizedPath)
         {
-            var expirationTokens = new List<IChangeToken>()
+            IList<IChangeToken> expirationTokens = Array.Empty<IChangeToken>();
+
+            if (AllowRecompilingViewsOnFileChange)
             {
-                _fileProvider.Watch(normalizedPath),
+                var changeToken = _fileProvider.Watch(normalizedPath);
-            };
+                expirationTokens = new List<IChangeToken> { changeToken };
+            }
 
             var projectItem = _projectEngine.FileSystem.GetItem(normalizedPath);
             if (!projectItem.Exists)
@@ -313,9 +311,46 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 
             _logger.ViewCompilerFoundFileToCompile(normalizedPath);
 
+            GetChangeTokensFromImports(expirationTokens, projectItem);
+
+            return new ViewCompilerWorkItem()
+            {
+                SupportsCompilation = true,
+
+                NormalizedPath = normalizedPath,
+                ExpirationTokens = expirationTokens,
+            };
+        }
+
+        private IList<IChangeToken> GetExpirationTokens(CompiledViewDescriptor precompiledView)
+        {
+            if (!AllowRecompilingViewsOnFileChange)
+            {
+                return Array.Empty<IChangeToken>();
+            }
+
+            var checksums = precompiledView.Item.GetChecksumMetadata();
+            var expirationTokens = new List<IChangeToken>(checksums.Count);
+
+            for (var i = 0; i < checksums.Count; i++)
+            {
+                // We rely on Razor to provide the right set of checksums. Trust the compiler, it has to do a good job,
+                // so it probably will.
+                expirationTokens.Add(_fileProvider.Watch(checksums[i].Identifier));
+            }
+
+            return expirationTokens;
+        }
+
+        private void GetChangeTokensFromImports(IList<IChangeToken> expirationTokens, RazorProjectItem projectItem)
+        {
+            if (!AllowRecompilingViewsOnFileChange)
+            {
+                return;
+            }
+
             // OK this means we can do compilation. For now let's just identify the other files we need to watch
             // so we can create the cache entry. Compilation will happen after we release the lock.
-
             var importFeature = _projectEngine.ProjectFeatures.OfType<IImportProjectFeature>().FirstOrDefault();
 
             // There should always be an import feature unless someone has misconfigured their RazorProjectEngine.
@@ -330,14 +365,6 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             {
                 expirationTokens.Add(_fileProvider.Watch(physicalImport.FilePath));
             }
-
-            return new ViewCompilerWorkItem()
-            {
-                SupportsCompilation = true,
-
-                NormalizedPath = normalizedPath,
-                ExpirationTokens = expirationTokens,
-            };
         }
 
         protected virtual CompiledViewDescriptor CompileAndEmit(string relativePath)

src/Microsoft.AspNetCore.Mvc.Razor/Internal/RazorViewCompilerProvider.cs

@@ -80,7 +80,10 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 #pragma warning restore CS0618 // Type or member is obsolete
                 feature.ViewDescriptors,
                 _compilationMemoryCacheProvider.CompilationMemoryCache,
-                _logger);
+                _logger)
+            {
+                AllowRecompilingViewsOnFileChange = _viewEngineOptions.AllowRecompilingViewsOnFileChange,
+            };
         }
     }
 }

src/Microsoft.AspNetCore.Mvc.Razor/Properties/AssemblyInfo.cs

@@ -7,3 +7,4 @@ using System.Runtime.CompilerServices;
 
 [assembly: InternalsVisibleTo("Microsoft.AspNetCore.Mvc.Test, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 [assembly: InternalsVisibleTo("Microsoft.AspNetCore.Mvc.Razor.Test, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
+[assembly: InternalsVisibleTo("Microsoft.AspNetCore.Mvc.RazorPages.Test, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]

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

@@ -2,8 +2,10 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.Razor.Compilation;
 using Microsoft.CodeAnalysis;
 using Microsoft.Extensions.FileProviders;
@@ -13,10 +15,21 @@ namespace Microsoft.AspNetCore.Mvc.Razor
     /// <summary>
     /// Provides programmatic configuration for the <see cref="RazorViewEngine"/>.
     /// </summary>
-    public class RazorViewEngineOptions
+    public class RazorViewEngineOptions : IEnumerable<ICompatibilitySwitch>
     {
+        private readonly ICompatibilitySwitch[] _switches;
+        private readonly CompatibilitySwitch<bool> _allowRecompilingViewsOnFileChange;
         private Action<RoslynCompilationContext> _compilationCallback = c => { };
 
+        public RazorViewEngineOptions()
+        {
+            _allowRecompilingViewsOnFileChange = new CompatibilitySwitch<bool>(nameof(AllowRecompilingViewsOnFileChange));
+            _switches = new[]
+            {
+                _allowRecompilingViewsOnFileChange,
+            };
+        }
+
         /// <summary>
         /// Gets a <see cref="IList{IViewLocationExpander}"/> used by the <see cref="RazorViewEngine"/>.
         /// </summary>
@@ -181,5 +194,52 @@ namespace Microsoft.AspNetCore.Mvc.Razor
                 _compilationCallback = value;
             }
         }
+
+        /// <summary>
+        /// Gets or sets a value that determines if Razor files (Razor Views and Razor Pages) are recompiled and updated 
+        /// if files change on disk.
+        /// <para>
+        /// When <see langword="true"/>, MVC will use <see cref="IFileProvider.Watch(string)"/> to watch for changes to 
+        /// Razor files in configured <see cref="IFileProvider"/> instances.
+        /// </para>
+        /// </summary>
+        /// <value>
+        /// The default value is <see langword="true"/> if the version is <see cref = "CompatibilityVersion.Version_2_1" />
+        /// or earlier. If the version is later and <see cref= "IHostingEnvironment.EnvironmentName" /> is <c>Development</c>,
+        /// the default value is <see langword="true"/>. Otherwise, the default value is <see langword="false" />.
+        /// </value>
+        /// <remarks>
+        /// <para>
+        /// This property is associated with a compatibility switch and can provide a different behavior depending on
+        /// the configured compatibility version for the application. See <see cref="CompatibilityVersion"/> for
+        /// guidance and examples of setting the application's compatibility version.
+        /// </para>
+        /// <para>
+        /// Configuring the desired value of the compatibility switch by calling this property's setter will take
+        /// precedence over the value implied by the application's <see cref="CompatibilityVersion"/>.
+        /// </para>
+        /// <para>
+        /// If the application's compatibility version is set to <see cref="CompatibilityVersion.Version_2_1"/> or
+        /// lower then this setting will have the value <see langword="true"/> unless explicitly configured.
+        /// </para>
+        /// <para>
+        /// If the application's compatibility version is set to <see cref="CompatibilityVersion.Version_2_2"/> or
+        /// higher then this setting will have the value <see langword="false"/> unless
+        /// <see cref="IHostingEnvironment.EnvironmentName"/>  is <c>Development</c> or the value is explicitly configured.
+        /// </para>
+        /// </remarks>
+        public bool AllowRecompilingViewsOnFileChange
+        {
+            // Note: When compatibility switches are removed in 3.0, this property should be retained as a regular boolean property.
+            get => _allowRecompilingViewsOnFileChange.Value;
+            set => _allowRecompilingViewsOnFileChange.Value = value;
+        }
+
+        IEnumerator<ICompatibilitySwitch> IEnumerable<ICompatibilitySwitch>.GetEnumerator()
+        {
+            return ((IEnumerable<ICompatibilitySwitch>)_switches).GetEnumerator();
+        }
+
+        IEnumerator IEnumerable.GetEnumerator() => _switches.GetEnumerator();
     }
 }

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

@@ -2,27 +2,45 @@
 // 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 Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
+using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 
-namespace Microsoft.AspNetCore.Mvc.Razor.Internal
+namespace Microsoft.AspNetCore.Mvc.Razor
 {
-    /// <summary>
+    internal class RazorViewEngineOptionsSetup :
-    /// Sets up default options for <see cref="RazorViewEngineOptions"/>.
+        ConfigureCompatibilityOptions<RazorViewEngineOptions>, 
-    /// </summary>
+        IConfigureOptions<RazorViewEngineOptions>
-    public class RazorViewEngineOptionsSetup : IConfigureOptions<RazorViewEngineOptions>
     {
         private readonly IHostingEnvironment _hostingEnvironment;
 
-        /// <summary>
+        public RazorViewEngineOptionsSetup(
-        /// Initializes a new instance of <see cref="RazorViewEngineOptions"/>.
+            IHostingEnvironment hostingEnvironment,
-        /// </summary>
+            ILoggerFactory loggerFactory,
-        /// <param name="hostingEnvironment"><see cref="IHostingEnvironment"/> for the application.</param>
+            IOptions<MvcCompatibilityOptions> compatibilityOptions)
-        public RazorViewEngineOptionsSetup(IHostingEnvironment hostingEnvironment)
+            : base(loggerFactory, compatibilityOptions)
         {
             _hostingEnvironment = hostingEnvironment ?? throw new ArgumentNullException(nameof(hostingEnvironment));
         }
 
+        protected override IReadOnlyDictionary<string, object> DefaultValues
+        {
+            get
+            {
+                var values = new Dictionary<string, object>();
+                if (Version < CompatibilityVersion.Version_2_2)
+                {
+                    // Default to true in 2.1 or earlier. In 2.2, we have to conditionally enable this
+                    // and consequently this switch has no default value.
+                    values[nameof(RazorViewEngineOptions.AllowRecompilingViewsOnFileChange)] = true;
+                }
+
+                return values;
+            }
+        }
+
         public void Configure(RazorViewEngineOptions options)
         {
             if (options == null)
@@ -41,6 +59,11 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             options.AreaViewLocationFormats.Add("/Areas/{2}/Views/{1}/{0}" + RazorViewEngine.ViewExtension);
             options.AreaViewLocationFormats.Add("/Areas/{2}/Views/Shared/{0}" + RazorViewEngine.ViewExtension);
             options.AreaViewLocationFormats.Add("/Views/Shared/{0}" + RazorViewEngine.ViewExtension);
+
+            if (_hostingEnvironment.IsDevelopment())
+            {
+                options.AllowRecompilingViewsOnFileChange = true;
+            }
         }
     }
 }

src/Microsoft.AspNetCore.Mvc.RazorPages/Internal/PageActionDescriptorChangeProvider.cs

@@ -5,6 +5,7 @@ using System;
 using System.Diagnostics;
 using System.Linq;
 using Microsoft.AspNetCore.Mvc.Infrastructure;
+using Microsoft.AspNetCore.Mvc.Razor;
 using Microsoft.AspNetCore.Mvc.Razor.Internal;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.Extensions.FileProviders;
@@ -18,11 +19,13 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
         private readonly IFileProvider _fileProvider;
         private readonly string[] _searchPatterns;
         private readonly string[] _additionalFilesToTrack;
+        private readonly bool _watchForChanges;
 
         public PageActionDescriptorChangeProvider(
             RazorTemplateEngine templateEngine,
             IRazorViewEngineFileProviderAccessor fileProviderAccessor,
-            IOptions<RazorPagesOptions> razorPagesOptions)
+            IOptions<RazorPagesOptions> razorPagesOptions,
+            IOptions<RazorViewEngineOptions> razorViewEngineOptions)
         {
             if (templateEngine == null)
             {
@@ -39,6 +42,13 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 throw new ArgumentNullException(nameof(razorPagesOptions));
             }
 
+            _watchForChanges = razorViewEngineOptions.Value.AllowRecompilingViewsOnFileChange;
+            if (!_watchForChanges)
+            {
+                // No need to do any additional work if we aren't going to be watching for file changes.
+                return;
+            }
+
             _fileProvider = fileProviderAccessor.FileProvider;
 
             var rootDirectory = razorPagesOptions.Value.RootDirectory;
@@ -84,6 +94,11 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
 
         public IChangeToken GetChangeToken()
         {
+            if (!_watchForChanges)
+            {
+                return NullChangeToken.Singleton;
+            }
+
             var changeTokens = new IChangeToken[_additionalFilesToTrack.Length + _searchPatterns.Length];
             for (var i = 0; i < _additionalFilesToTrack.Length; i++)
             {

test/Microsoft.AspNetCore.Mvc.FunctionalTests/RazorFileUpdateTests.cs

@@ -0,0 +1,131 @@
+// 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.Net.Http;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Mvc.Razor;
+using Microsoft.AspNetCore.TestHost;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.FunctionalTests
+{
+    // Verifies that updating Razor files (views and pages) with AllowRecompilingViewsOnFileChange=true works
+    public class RazorFileUpdateTests : IClassFixture<MvcTestFixture<RazorWebSite.Startup>>
+    {
+        public RazorFileUpdateTests(MvcTestFixture<RazorWebSite.Startup> fixture)
+        {
+            var factory = fixture.WithWebHostBuilder(builder =>
+            {
+                builder.UseStartup<RazorWebSite.Startup>();
+                builder.ConfigureTestServices(services =>
+                {
+                    services.Configure<RazorViewEngineOptions>(options => options.AllowRecompilingViewsOnFileChange = true);
+                });
+            });
+            Client = factory.CreateDefaultClient();
+        }
+
+        public HttpClient Client { get; }
+
+        [Fact]
+        public async Task RazorViews_AreUpdatedOnChange()
+        {
+            // Arrange
+            var expected1 = "Original content";
+            var expected2 = "New content";
+            var path = "/Views/UpdateableShared/_Partial.cshtml";
+
+            // Act - 1
+            var body = await Client.GetStringAsync("/UpdateableFileProvider");
+
+            // Assert - 1
+            Assert.Equal(expected1, body.Trim(), ignoreLineEndingDifferences: true);
+
+            // Act - 2
+            await UpdateFile(path, expected2);
+            body = await Client.GetStringAsync("/UpdateableFileProvider");
+
+            // Assert - 2
+            Assert.Equal(expected2, body.Trim(), ignoreLineEndingDifferences: true);
+        }
+
+        [Fact]
+        public async Task RazorViews_AreUpdatedWhenViewImportsChange()
+        {
+            // Arrange
+            var content = "@GetType().Assembly.FullName";
+            await UpdateFile("/Views/UpdateableIndex/Index.cshtml", content);
+            var initial = await Client.GetStringAsync("/UpdateableFileProvider");
+
+            // Act
+            // Trigger a change in ViewImports
+            await UpdateFile("/Views/UpdateableIndex/_ViewImports.cshtml", string.Empty);
+            var updated = await Client.GetStringAsync("/UpdateableFileProvider");
+
+            // Assert
+            Assert.NotEqual(initial, updated);
+        }
+
+        [Fact]
+        public async Task RazorPages_AreUpdatedOnChange()
+        {
+            // Arrange
+            var expected1 = "Original content";
+            var expected2 = "New content";
+
+            // Act - 1
+            var body = await Client.GetStringAsync("/UpdateablePage");
+
+            // Assert - 1
+            Assert.Equal(expected1, body.Trim(), ignoreLineEndingDifferences: true);
+
+            // Act - 2
+            await UpdateRazorPages();
+            await UpdateFile("/Pages/UpdateablePage.cshtml", "@page" + Environment.NewLine + expected2);
+            body = await Client.GetStringAsync("/UpdateablePage");
+
+            // Assert - 2
+            Assert.Equal(expected2, body.Trim(), ignoreLineEndingDifferences: true);
+        }
+
+        [Fact]
+        public async Task RazorPages_AreUpdatedWhenViewImportsChange()
+        {
+            // Arrange
+            var content = "@GetType().Assembly.FullName";
+            await UpdateFile("/Pages/UpdateablePage.cshtml", "@page" + Environment.NewLine + content);
+            var initial = await Client.GetStringAsync("/UpdateablePage");
+
+            // Act
+            // Trigger a change in ViewImports
+            await UpdateRazorPages();
+            await UpdateFile("/Pages/UpdateablePage.cshtml", "@page" + Environment.NewLine + content);
+            var updated = await Client.GetStringAsync("/UpdateablePage");
+
+            // Assert
+            Assert.NotEqual(initial, updated);
+        }
+
+        private async Task UpdateFile(string path, string content)
+        {
+            var updateContent = new FormUrlEncodedContent(new Dictionary<string, string>
+            {
+                { "path", path },
+                { "content", content },
+            });
+
+            var response = await Client.PostAsync($"/UpdateableFileProvider/Update", updateContent);
+            response.EnsureSuccessStatusCode();
+        }
+
+        private async Task UpdateRazorPages()
+        {
+            var response = await Client.PostAsync($"/UpdateableFileProvider/UpdateRazorPages", new StringContent(string.Empty));
+            response.EnsureSuccessStatusCode();
+        }
+    }
+}

test/Microsoft.AspNetCore.Mvc.FunctionalTests/ViewEngineTests.cs

@@ -270,28 +270,6 @@ Hello from Shared/_EmbeddedPartial
             Assert.Equal(expected, body.Trim(), ignoreLineEndingDifferences: true);
         }
 
-        [Fact]
-        public async Task RazorViewEngine_UpdatesViewsReferencedViaRelativePathsOnChange()
-        {
-            // Arrange
-            var expected1 = "Original content";
-            var expected2 = "New content";
-
-            // Act - 1
-            var body = await Client.GetStringAsync("/UpdateableFileProvider");
-
-            // Assert - 1
-            Assert.Equal(expected1, body.Trim(), ignoreLineEndingDifferences: true);
-
-            // Act - 2
-            var response = await Client.PostAsync("/UpdateableFileProvider/Update", new StringContent(string.Empty));
-            response.EnsureSuccessStatusCode();
-            body = await Client.GetStringAsync("/UpdateableFileProvider");
-
-            // Assert - 1
-            Assert.Equal(expected2, body.Trim(), ignoreLineEndingDifferences: true);
-        }
-
         [Fact]
         public async Task LayoutValueIsPassedBetweenNestedViewStarts()
         {

test/Microsoft.AspNetCore.Mvc.Razor.Test/Internal/RazorViewCompilerTest.cs

@@ -37,6 +37,25 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             var result1 = await viewCompiler.CompileAsync(path);
             var result2 = await viewCompiler.CompileAsync(path);
 
+            // Assert
+            Assert.Same(result1, result2);
+            Assert.Null(result1.ViewAttribute);
+            Assert.Empty(result1.ExpirationTokens);
+        }
+
+        [Fact]
+        public async Task CompileAsync_ReturnsResultWithExpirationToken_WhenWatchingForFileChanges()
+        {
+            // Arrange
+            var path = "/file/does-not-exist";
+            var fileProvider = new TestFileProvider();
+            var viewCompiler = GetViewCompiler(fileProvider);
+            viewCompiler.AllowRecompilingViewsOnFileChange = true;
+
+            // Act
+            var result1 = await viewCompiler.CompileAsync(path);
+            var result2 = await viewCompiler.CompileAsync(path);
+
             // Assert
             Assert.Same(result1, result2);
             Assert.Null(result1.ViewAttribute);
@@ -57,6 +76,24 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             // Act
             var result = await viewCompiler.CompileAsync(path);
 
+            // Assert
+            Assert.NotNull(result.ViewAttribute);
+            Assert.Empty(result.ExpirationTokens);
+        }
+
+        [Fact]
+        public async Task CompileAsync_AddsChangeTokensForViewStartsIfFileExists_WhenWatchingForFileChanges()
+        {
+            // Arrange
+            var path = "/file/exists/FilePath.cshtml";
+            var fileProvider = new TestFileProvider();
+            fileProvider.AddFile(path, "Content");
+            var viewCompiler = GetViewCompiler(fileProvider);
+            viewCompiler.AllowRecompilingViewsOnFileChange = true;
+
+            // Act
+            var result = await viewCompiler.CompileAsync(path);
+
             // Assert
             Assert.NotNull(result.ViewAttribute);
             Assert.Collection(
@@ -92,13 +129,40 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
         }
 
         [Fact]
-        public async Task CompileAsync_InvalidatesCache_IfChangeTokenExpires()
+        public async Task CompileAsync_DoesNotInvalidCache_IfChangeTokenChanges()
         {
             // Arrange
             var path = "/Views/Home/Index.cshtml";
             var fileProvider = new TestFileProvider();
             var fileInfo = fileProvider.AddFile(path, "some content");
             var viewCompiler = GetViewCompiler(fileProvider);
+            var changeToken = fileProvider.Watch(path);
+
+            // Act 1
+            var result1 = await viewCompiler.CompileAsync(path);
+
+            // Assert 1
+            Assert.NotNull(result1.ViewAttribute);
+
+            // Act 2
+            fileProvider.DeleteFile(path);
+            fileProvider.GetChangeToken(path).HasChanged = true;
+            viewCompiler.Compile = _ => throw new Exception("Can't call me");
+            var result2 = await viewCompiler.CompileAsync(path);
+
+            // Assert 2
+            Assert.Same(result1, result2);
+        }
+
+        [Fact]
+        public async Task CompileAsync_InvalidatesCache_IfChangeTokenExpires_WhenWatchingForFileChanges()
+        {
+            // Arrange
+            var path = "/Views/Home/Index.cshtml";
+            var fileProvider = new TestFileProvider();
+            var fileInfo = fileProvider.AddFile(path, "some content");
+            var viewCompiler = GetViewCompiler(fileProvider);
+            viewCompiler.AllowRecompilingViewsOnFileChange = true;
 
             // Act 1
             var result1 = await viewCompiler.CompileAsync(path);
@@ -125,6 +189,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             var fileProvider = new TestFileProvider();
             var fileInfo = fileProvider.AddFile(path, "some content");
             var viewCompiler = GetViewCompiler(fileProvider);
+            viewCompiler.AllowRecompilingViewsOnFileChange = true;
             var expected2 = new CompiledViewDescriptor();
 
             // Act 1
@@ -151,6 +216,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             var fileProvider = new TestFileProvider();
             var fileInfo = fileProvider.AddFile(path, "some content");
             var viewCompiler = GetViewCompiler(fileProvider);
+            viewCompiler.AllowRecompilingViewsOnFileChange = true;
             var expected2 = new CompiledViewDescriptor();
 
             // Act 1
@@ -327,6 +393,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             };
 
             var viewCompiler = GetViewCompiler(fileProvider, precompiledViews: new[] { precompiledView });
+            viewCompiler.AllowRecompilingViewsOnFileChange = true;
 
             // Act
             var result = await viewCompiler.CompileAsync(path);
@@ -371,7 +438,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
         }
 
         [Fact]
-        public async Task CompileAsync_PrecompiledViewWithChecksum_CanRecompile()
+        public async Task CompileAsync_PrecompiledViewWithChecksum_DoesNotAddExpirationTokens()
         {
             // Arrange
             var path = "/Views/Home/Index.cshtml";
@@ -392,11 +459,43 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 
             var viewCompiler = GetViewCompiler(fileProvider, precompiledViews: new[] { precompiledView });
 
+            // Act
+            var result = await viewCompiler.CompileAsync(path);
+
+            // Assert
+            Assert.Same(precompiledView.Item, result.Item);
+            Assert.Empty(result.ExpirationTokens);
+        }
+
+        [Fact]
+        public async Task CompileAsync_PrecompiledViewWithChecksum_CanRecompile()
+        {
+            // Arrange
+            var path = "/Views/Home/Index.cshtml";
+
+            var fileProvider = new TestFileProvider();
+            var fileInfo = fileProvider.AddFile(path, "some content");
+
+            var expected2 = new CompiledViewDescriptor();
+
+            var precompiledView = new CompiledViewDescriptor
+            {
+                RelativePath = path,
+                Item = new TestRazorCompiledItem(typeof(string), "mvc.1.0.view", path, new object[]
+                {
+                    new RazorSourceChecksumAttribute("SHA1", GetChecksum("some content"), path),
+                }),
+            };
+
+            var viewCompiler = GetViewCompiler(fileProvider, precompiledViews: new[] { precompiledView });
+            viewCompiler.AllowRecompilingViewsOnFileChange = true;
+
             // Act - 1
             var result = await viewCompiler.CompileAsync(path);
 
             // Assert - 1
             Assert.Same(precompiledView.Item, result.Item);
+            Assert.NotEmpty(result.ExpirationTokens);
 
             // Act - 2
             fileInfo.Content = "some other content";
@@ -427,6 +526,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             };
 
             var viewCompiler = GetViewCompiler(fileProvider, precompiledViews: new[] { precompiledView });
+            viewCompiler.AllowRecompilingViewsOnFileChange = true;
 
             // Act - 1
             var result = await viewCompiler.CompileAsync(path);
@@ -463,6 +563,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             };
 
             var viewCompiler = GetViewCompiler(fileProvider, precompiledViews: new[] { precompiledView });
+            viewCompiler.AllowRecompilingViewsOnFileChange = true;
             viewCompiler.Compile = _ => expected1;
 
             // Act - 1
@@ -504,6 +605,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             };
 
             var viewCompiler = GetViewCompiler(fileProvider, precompiledViews: new[] { precompiledView });
+            viewCompiler.AllowRecompilingViewsOnFileChange = true;
 
             // Act - 1
             var result = await viewCompiler.CompileAsync(path);

test/Microsoft.AspNetCore.Mvc.Razor.Test/Internal/RazorViewEngineOptionsSetupTest.cs

@@ -2,7 +2,11 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
+using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.FileProviders;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
 using Moq;
 using Xunit;
 
@@ -19,7 +23,8 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             var hostingEnv = new Mock<IHostingEnvironment>();
             hostingEnv.SetupGet(e => e.ContentRootFileProvider)
                 .Returns(expected);
-            var optionsSetup = new RazorViewEngineOptionsSetup(hostingEnv.Object);
+
+            var optionsSetup = GetSetup(hostingEnvironment: hostingEnv.Object);
 
             // Act
             optionsSetup.Configure(options);
@@ -28,5 +33,128 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             var fileProvider = Assert.Single(options.FileProviders);
             Assert.Same(expected, fileProvider);
         }
+
+        [Fact]
+        public void PostConfigure_SetsAllowRecompilingViewsOnFileChange_For21()
+        {
+            // Arrange
+            var options = new RazorViewEngineOptions();
+            var optionsSetup = GetSetup(CompatibilityVersion.Version_2_1);
+
+            // Act
+            optionsSetup.Configure(options);
+            optionsSetup.PostConfigure(string.Empty, options);
+
+            // Assert
+            Assert.True(options.AllowRecompilingViewsOnFileChange);
+        }
+
+        [Theory]
+        [InlineData(CompatibilityVersion.Version_2_2)]
+        [InlineData(CompatibilityVersion.Latest)]
+        public void PostConfigure_SetsAllowRecompilingViewsOnFileChange_InDevelopmentMode(CompatibilityVersion compatibilityVersion)
+        {
+            // Arrange
+            var options = new RazorViewEngineOptions();
+            var hostingEnv = Mock.Of<IHostingEnvironment>(env => env.EnvironmentName == EnvironmentName.Development);
+            var optionsSetup = GetSetup(compatibilityVersion, hostingEnv);
+
+            // Act
+            optionsSetup.Configure(options);
+            optionsSetup.PostConfigure(string.Empty, options);
+
+            // Assert
+            Assert.True(options.AllowRecompilingViewsOnFileChange);
+        }
+
+        [Theory]
+        [InlineData(CompatibilityVersion.Version_2_2)]
+        [InlineData(CompatibilityVersion.Latest)]
+        public void PostConfigure_DoesNotSetAllowRecompilingViewsOnFileChange_WhenNotInDevelopment(CompatibilityVersion compatibilityVersion)
+        {
+            // Arrange
+            var options = new RazorViewEngineOptions();
+            var hostingEnv = Mock.Of<IHostingEnvironment>(env => env.EnvironmentName == EnvironmentName.Staging);
+            var optionsSetup = GetSetup(compatibilityVersion, hostingEnv);
+
+            // Act
+            optionsSetup.Configure(options);
+            optionsSetup.PostConfigure(string.Empty, options);
+
+            // Assert
+            Assert.False(options.AllowRecompilingViewsOnFileChange);
+        }
+
+        [Fact]
+        public void RazorViewEngineOptionsSetup_DoesNotOverwriteAllowRecompilingViewsOnFileChange_In21CompatMode()
+        {
+            // Arrange
+            var hostingEnv = Mock.Of<IHostingEnvironment>(env => env.EnvironmentName == EnvironmentName.Staging);
+            var compatibilityVersion = new MvcCompatibilityOptions { CompatibilityVersion = CompatibilityVersion.Version_2_1 };
+            var optionsSetup = GetSetup(CompatibilityVersion.Version_2_1, hostingEnv);
+            var serviceProvider = new ServiceCollection()
+                .AddOptions()
+                .AddSingleton<IConfigureOptions<RazorViewEngineOptions>>(optionsSetup)
+                .Configure<RazorViewEngineOptions>(o => o.AllowRecompilingViewsOnFileChange = false)
+                .BuildServiceProvider();
+
+            // Act
+            var options = serviceProvider.GetRequiredService<IOptions<RazorViewEngineOptions>>();
+
+            // Assert
+            Assert.False(options.Value.AllowRecompilingViewsOnFileChange);
+        }
+
+        [Fact]
+        public void RazorViewEngineOptionsSetup_ConfiguresAllowRecompilingViewsOnFileChange()
+        {
+            // Arrange
+            var hostingEnv = Mock.Of<IHostingEnvironment>(env => env.EnvironmentName == EnvironmentName.Production);
+            var compatibilityVersion = new MvcCompatibilityOptions { CompatibilityVersion = CompatibilityVersion.Version_2_2 };
+            var optionsSetup = GetSetup(CompatibilityVersion.Version_2_2, hostingEnv);
+            var serviceProvider = new ServiceCollection()
+                .AddOptions()
+                .AddSingleton<IConfigureOptions<RazorViewEngineOptions>>(optionsSetup)
+                .BuildServiceProvider();
+
+            // Act
+            var options = serviceProvider.GetRequiredService<IOptions<RazorViewEngineOptions>>();
+
+            // Assert
+            Assert.False(options.Value.AllowRecompilingViewsOnFileChange);
+        }
+
+        [Fact]
+        public void RazorViewEngineOptionsSetup_DoesNotOverwriteAllowRecompilingViewsOnFileChange()
+        {
+            // Arrange
+            var hostingEnv = Mock.Of<IHostingEnvironment>(env => env.EnvironmentName == EnvironmentName.Production);
+            var optionsSetup = GetSetup(CompatibilityVersion.Version_2_2, hostingEnv);
+            var serviceProvider = new ServiceCollection()
+                .AddOptions()
+                .AddSingleton<IConfigureOptions<RazorViewEngineOptions>>(optionsSetup)
+                .Configure<RazorViewEngineOptions>(o => o.AllowRecompilingViewsOnFileChange = true)
+                .BuildServiceProvider();
+
+            // Act
+            var options = serviceProvider.GetRequiredService<IOptions<RazorViewEngineOptions>>();
+
+            // Assert
+            Assert.True(options.Value.AllowRecompilingViewsOnFileChange);
+        }
+
+        private static RazorViewEngineOptionsSetup GetSetup(
+            CompatibilityVersion compatibilityVersion = CompatibilityVersion.Latest,
+            IHostingEnvironment hostingEnvironment = null)
+        {
+            hostingEnvironment = hostingEnvironment ?? Mock.Of<IHostingEnvironment>();
+            var compatibilityOptions = new MvcCompatibilityOptions { CompatibilityVersion = compatibilityVersion };
+
+            return new RazorViewEngineOptionsSetup(
+                hostingEnvironment,
+                NullLoggerFactory.Instance,
+                Options.Create(compatibilityOptions));
+        }
+
     }
 }

test/Microsoft.AspNetCore.Mvc.Razor.Test/RazorViewEngineTest.cs

@@ -8,6 +8,7 @@ using System.Threading;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.Abstractions;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.Razor.Compilation;
 using Microsoft.AspNetCore.Mvc.Razor.Internal;
 using Microsoft.AspNetCore.Mvc.Routing;
@@ -1979,7 +1980,10 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             IEnumerable<string> areaViewLocationFormats = null,
             IEnumerable<string> pageViewLocationFormats = null)
         {
-            var optionsSetup = new RazorViewEngineOptionsSetup(Mock.Of<IHostingEnvironment>());
+            var optionsSetup = new RazorViewEngineOptionsSetup(
+                Mock.Of<IHostingEnvironment>(),
+                NullLoggerFactory.Instance,
+                Options.Create(new MvcCompatibilityOptions()));
 
             var options = new RazorViewEngineOptions();
             optionsSetup.Configure(options);

test/Microsoft.AspNetCore.Mvc.RazorPages.Test/Internal/PageActionDescriptorChangeProviderTest.cs

@@ -30,8 +30,9 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
             var templateEngine = new RazorTemplateEngine(
                 RazorProjectEngine.Create(RazorConfiguration.Default, fileSystem).Engine,
                 fileSystem);
-            var options = Options.Create(new RazorPagesOptions());
+            var razorPageOptions = Options.Create(new RazorPagesOptions());
-            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options);
+            var razorViewEngineOptions = Options.Create(new RazorViewEngineOptions { AllowRecompilingViewsOnFileChange = true });
+            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, razorPageOptions, razorViewEngineOptions);
 
             // Act
             var changeToken = changeProvider.GetChangeToken();
@@ -57,8 +58,9 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 fileSystem);
             var options = Options.Create(new RazorPagesOptions());
             options.Value.RootDirectory = rootDirectory;
+            var razorViewEngineOptions = Options.Create(new RazorViewEngineOptions { AllowRecompilingViewsOnFileChange = true });
 
-            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options);
+            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options, razorViewEngineOptions);
 
             // Act
             var changeToken = changeProvider.GetChangeToken();
@@ -81,7 +83,8 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 RazorProjectEngine.Create(RazorConfiguration.Default, fileSystem).Engine,
                 fileSystem);
             var options = Options.Create(new RazorPagesOptions { AllowAreas = true });
-            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options);
+            var razorViewEngineOptions = Options.Create(new RazorViewEngineOptions { AllowRecompilingViewsOnFileChange = true });
+            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options, razorViewEngineOptions);
 
             // Act
             var changeToken = changeProvider.GetChangeToken();
@@ -104,8 +107,9 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
             templateEngine.Options.ImportsFileName = "_ViewImports.cshtml";
             var options = Options.Create(new RazorPagesOptions());
             options.Value.RootDirectory = "/dir1/dir2";
+            var razorViewEngineOptions = Options.Create(new RazorViewEngineOptions { AllowRecompilingViewsOnFileChange = true });
 
-            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options);
+            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options, razorViewEngineOptions);
 
             // Act & Assert
             var compositeChangeToken = Assert.IsType<CompositeChangeToken>(changeProvider.GetChangeToken());
@@ -131,7 +135,8 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
             options.Value.RootDirectory = "/dir1/dir2";
             options.Value.AllowAreas = true;
 
-            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options);
+            var razorViewEngineOptions = Options.Create(new RazorViewEngineOptions { AllowRecompilingViewsOnFileChange = true });
+            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options, razorViewEngineOptions);
 
             // Act & Assert
             var compositeChangeToken = Assert.IsType<CompositeChangeToken>(changeProvider.GetChangeToken());
@@ -155,8 +160,9 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 fileSystem);
             templateEngine.Options.ImportsFileName = "_ViewImports.cshtml";
             var options = Options.Create(new RazorPagesOptions { AllowAreas = false });
+            var razorViewEngineOptions = Options.Create(new RazorViewEngineOptions { AllowRecompilingViewsOnFileChange = true });
 
-            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options);
+            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options, razorViewEngineOptions);
 
             // Act & Assert
             var compositeChangeToken = Assert.IsType<CompositeChangeToken>(changeProvider.GetChangeToken());
@@ -164,5 +170,27 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 changeToken => Assert.Same(fileProvider.GetChangeToken("/_ViewImports.cshtml"), changeToken),
                 changeToken => Assert.Same(fileProvider.GetChangeToken("/Pages/**/*.cshtml"), changeToken));
         }
+
+        [Fact]
+        public void GetChangeToken_DoesNotWatch_WhenOptionIsReset()
+        {
+            // Arrange
+            var fileProvider = new Mock<IFileProvider>(MockBehavior.Strict);
+            var accessor = Mock.Of<IRazorViewEngineFileProviderAccessor>(a => a.FileProvider == fileProvider.Object);
+
+            var fileSystem = new FileProviderRazorProjectFileSystem(accessor, _hostingEnvironment);
+            var templateEngine = new RazorTemplateEngine(
+                RazorProjectEngine.Create(RazorConfiguration.Default, fileSystem).Engine,
+                fileSystem);
+            templateEngine.Options.ImportsFileName = "_ViewImports.cshtml";
+            var options = Options.Create(new RazorPagesOptions());
+            var razorViewEngineOptions = Options.Create(new RazorViewEngineOptions());
+
+            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, accessor, options, razorViewEngineOptions);
+
+            // Act & Assert
+            var compositeChangeToken = Assert.IsType<NullChangeToken>(changeProvider.GetChangeToken());
+            fileProvider.Verify(f => f.Watch(It.IsAny<string>()), Times.Never());
+        }
     }
 }

test/Microsoft.AspNetCore.Mvc.RazorPages.Test/Internal/RazorPagesRazorViewEngineOptionsSetupTest.cs

@@ -2,9 +2,10 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.Razor;
-using Microsoft.AspNetCore.Mvc.Razor.Internal;
 using Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure;
+using Microsoft.Extensions.Logging.Abstractions;
 using Microsoft.Extensions.Options;
 using Moq;
 using Xunit;
@@ -186,7 +187,10 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
 
         private static RazorViewEngineOptions GetViewEngineOptions()
         {
-            var defaultSetup = new RazorViewEngineOptionsSetup(Mock.Of<IHostingEnvironment>());
+            var defaultSetup = new RazorViewEngineOptionsSetup(
+                Mock.Of<IHostingEnvironment>(),
+                NullLoggerFactory.Instance,
+                Options.Create(new MvcCompatibilityOptions()));
             var options = new RazorViewEngineOptions();
             defaultSetup.Configure(options);
 

test/Microsoft.AspNetCore.Mvc.Test/IntegrationTest/CompatibilitySwitchIntegrationTest.cs

@@ -1,11 +1,14 @@
 // 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.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Mvc.Formatters;
+using Microsoft.AspNetCore.Mvc.Razor;
 using Microsoft.AspNetCore.Mvc.RazorPages;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.ObjectPool;
 using Microsoft.Extensions.Options;
+using Moq;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Mvc.IntegrationTest
@@ -32,6 +35,7 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTest
             var jsonOptions = services.GetRequiredService<IOptions<MvcJsonOptions>>().Value;
             var razorPagesOptions = services.GetRequiredService<IOptions<RazorPagesOptions>>().Value;
             var apiBehaviorOptions = services.GetRequiredService<IOptions<ApiBehaviorOptions>>().Value;
+            var razorViewEngineOptions = services.GetRequiredService<IOptions<RazorViewEngineOptions>>().Value;
 
             // Assert
             Assert.False(mvcOptions.AllowCombiningAuthorizeFilters);
@@ -44,6 +48,7 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTest
             Assert.Null(mvcOptions.MaxValidationDepth);
             Assert.True(apiBehaviorOptions.SuppressUseValidationProblemDetailsForInvalidModelStateResponses);
             Assert.True(apiBehaviorOptions.SuppressMapClientErrors);
+            Assert.True(razorViewEngineOptions.AllowRecompilingViewsOnFileChange);
         }
 
         [Fact]
@@ -61,6 +66,7 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTest
             var jsonOptions = services.GetRequiredService<IOptions<MvcJsonOptions>>().Value;
             var razorPagesOptions = services.GetRequiredService<IOptions<RazorPagesOptions>>().Value;
             var apiBehaviorOptions = services.GetRequiredService<IOptions<ApiBehaviorOptions>>().Value;
+            var razorViewEngineOptions = services.GetRequiredService<IOptions<RazorViewEngineOptions>>().Value;
 
             // Assert
             Assert.True(mvcOptions.AllowCombiningAuthorizeFilters);
@@ -73,6 +79,7 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTest
             Assert.Null(mvcOptions.MaxValidationDepth);
             Assert.True(apiBehaviorOptions.SuppressUseValidationProblemDetailsForInvalidModelStateResponses);
             Assert.True(apiBehaviorOptions.SuppressMapClientErrors);
+            Assert.True(razorViewEngineOptions.AllowRecompilingViewsOnFileChange);
         }
 
         [Fact]
@@ -90,6 +97,7 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTest
             var jsonOptions = services.GetRequiredService<IOptions<MvcJsonOptions>>().Value;
             var razorPagesOptions = services.GetRequiredService<IOptions<RazorPagesOptions>>().Value;
             var apiBehaviorOptions = services.GetRequiredService<IOptions<ApiBehaviorOptions>>().Value;
+            var razorViewEngineOptions = services.GetRequiredService<IOptions<RazorViewEngineOptions>>().Value;
 
             // Assert
             Assert.True(mvcOptions.AllowCombiningAuthorizeFilters);
@@ -102,6 +110,7 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTest
             Assert.Equal(32, mvcOptions.MaxValidationDepth);
             Assert.False(apiBehaviorOptions.SuppressUseValidationProblemDetailsForInvalidModelStateResponses);
             Assert.False(apiBehaviorOptions.SuppressMapClientErrors);
+            Assert.False(razorViewEngineOptions.AllowRecompilingViewsOnFileChange);
         }
 
         [Fact]
@@ -119,6 +128,7 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTest
             var jsonOptions = services.GetRequiredService<IOptions<MvcJsonOptions>>().Value;
             var razorPagesOptions = services.GetRequiredService<IOptions<RazorPagesOptions>>().Value;
             var apiBehaviorOptions = services.GetRequiredService<IOptions<ApiBehaviorOptions>>().Value;
+            var razorViewEngineOptions = services.GetRequiredService<IOptions<RazorViewEngineOptions>>().Value;
 
             // Assert
             Assert.True(mvcOptions.AllowCombiningAuthorizeFilters);
@@ -131,11 +141,13 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTest
             Assert.Equal(32, mvcOptions.MaxValidationDepth);
             Assert.False(apiBehaviorOptions.SuppressUseValidationProblemDetailsForInvalidModelStateResponses);
             Assert.False(apiBehaviorOptions.SuppressMapClientErrors);
+            Assert.False(razorViewEngineOptions.AllowRecompilingViewsOnFileChange);
         }
 
         // This just does the minimum needed to be able to resolve these options.
         private static void AddHostingServices(IServiceCollection serviceCollection)
         {
+            serviceCollection.AddSingleton(Mock.Of<IHostingEnvironment>());
             serviceCollection.AddLogging();
             serviceCollection.AddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();
         }

test/WebSites/RazorPagesWebSite/NonWatchingPhysicalFileProvider.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 System;
+using Microsoft.Extensions.FileProviders;
+using Microsoft.Extensions.Primitives;
+
+namespace RazorPagesWebSite
+{
+    public class NonWatchingPhysicalFileProvider : PhysicalFileProvider, IFileProvider
+    {
+        public NonWatchingPhysicalFileProvider(string root) : base(root)
+        {
+        }
+
+        IChangeToken IFileProvider.Watch(string filter) => throw new ArgumentException("This method should not be called.");
+    }
+}

test/WebSites/RazorPagesWebSite/StartupWithBasePath.cs

@@ -3,6 +3,7 @@
 
 using Microsoft.AspNetCore.Authentication.Cookies;
 using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.DependencyInjection;
 using RazorPagesWebSite.Conventions;
@@ -11,11 +12,18 @@ namespace RazorPagesWebSite
 {
     public class StartupWithBasePath
     {
+        private readonly IHostingEnvironment _hostingEnvironment;
+
+        public StartupWithBasePath(IHostingEnvironment hostingEnvironment)
+        {
+            _hostingEnvironment = hostingEnvironment;
+        }
+
         public void ConfigureServices(IServiceCollection services)
         {
             services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
                 .AddCookie(options => options.LoginPath = "/Login");
-            services.AddMvc()
+            var builder = services.AddMvc()
                 .AddCookieTempDataProvider()
                 .AddRazorPagesOptions(options =>
                 {
@@ -27,6 +35,14 @@ namespace RazorPagesWebSite
                     options.Conventions.Add(new CustomModelTypeConvention());
                 })
                 .SetCompatibilityVersion(CompatibilityVersion.Latest);
+
+            // Ensure we don't have code paths that call IFileProvider.Watch in the default code path.
+            // Comment this code block if you happen to run this site in Development.
+            builder.AddRazorOptions(options =>
+            {
+                options.FileProviders.Clear();
+                options.FileProviders.Add(new NonWatchingPhysicalFileProvider(_hostingEnvironment.ContentRootPath));
+            });
         }
 
         public void Configure(IApplicationBuilder app)

test/WebSites/RazorWebSite/Controllers/UpdateableFileProviderController.cs

@@ -10,9 +10,16 @@ namespace RazorWebSite
         public IActionResult Index() => View("/Views/UpdateableIndex/Index.cshtml");
 
         [HttpPost]
-        public IActionResult Update([FromServices] UpdateableFileProvider fileProvider)
+        public IActionResult Update([FromServices] UpdateableFileProvider fileProvider, string path, string content)
         {
-            fileProvider.UpdateContent("/Views/UpdateableShared/_Partial.cshtml", "New content");
+            fileProvider.UpdateContent(path, content);
+            return Ok();
+        }
+
+        [HttpPost]
+        public IActionResult UpdateRazorPages([FromServices] UpdateableFileProvider fileProvider)
+        {
+            fileProvider.CancelRazorPages();
             return Ok();
         }
     }

test/WebSites/RazorWebSite/Services/UpdateableFileProvider.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.IO;
 using System.Text;
@@ -13,8 +14,14 @@ namespace RazorWebSite
 {
     public class UpdateableFileProvider : IFileProvider
     {
+        public CancellationTokenSource _pagesTokenSource = new CancellationTokenSource();
+
         private readonly Dictionary<string, TestFileInfo> _content = new Dictionary<string, TestFileInfo>()
         {
+            {
+                "/Views/UpdateableIndex/_ViewImports.cshtml",
+                new TestFileInfo(string.Empty)
+            },
             {
                 "/Views/UpdateableIndex/Index.cshtml",
                 new TestFileInfo(@"@Html.Partial(""../UpdateableShared/_Partial.cshtml"")")
@@ -23,9 +30,21 @@ namespace RazorWebSite
                 "/Views/UpdateableShared/_Partial.cshtml",
                 new TestFileInfo("Original content")
             },
+            {
+                "/Pages/UpdateablePage.cshtml",
+                new TestFileInfo("@page" + Environment.NewLine + "Original content")
+            },
         };
 
-        public IDirectoryContents GetDirectoryContents(string subpath) => new NotFoundDirectoryContents();
+        public IDirectoryContents GetDirectoryContents(string subpath)
+        {
+            if (subpath == "/Pages")
+            {
+                return new PagesDirectoryContents();
+            }
+
+            return new NotFoundDirectoryContents();
+        }
 
         public void UpdateContent(string subpath, string content)
         {
@@ -34,10 +53,16 @@ namespace RazorWebSite
             _content[subpath] = new TestFileInfo(content);
         }
 
+        public void CancelRazorPages()
+        {
+            var oldToken = _pagesTokenSource;
+            _pagesTokenSource = new CancellationTokenSource();
+            oldToken.Cancel();
+        }
+
         public IFileInfo GetFileInfo(string subpath)
         {
-            TestFileInfo fileInfo;
+            if (!_content.TryGetValue(subpath, out var fileInfo))
-            if (!_content.TryGetValue(subpath, out fileInfo))
             {
                 fileInfo = new TestFileInfo(null);
             }
@@ -47,8 +72,12 @@ namespace RazorWebSite
 
         public IChangeToken Watch(string filter)
         {
-            TestFileInfo fileInfo;
+            if (filter == "/Pages/**/*.cshtml")
-            if (_content.TryGetValue(filter, out fileInfo))
+            {
+                return new CancellationChangeToken(_pagesTokenSource.Token);
+            }
+
+            if (_content.TryGetValue(filter, out var fileInfo))
             {
                 return fileInfo.ChangeToken;
             }
@@ -71,7 +100,7 @@ namespace RazorWebSite
             public bool IsDirectory => false;
             public DateTimeOffset LastModified => DateTimeOffset.MinValue;
             public long Length => -1;
-            public string Name => null;
+            public string Name { get; set; }
             public string PhysicalPath => null;
             public CancellationTokenSource TokenSource { get; } = new CancellationTokenSource();
             public CancellationChangeToken ChangeToken { get; }
@@ -81,5 +110,23 @@ namespace RazorWebSite
                 return new MemoryStream(Encoding.UTF8.GetBytes(_content));
             }
         }
+
+        private class PagesDirectoryContents : IDirectoryContents
+        {
+            public bool Exists => true;
+
+            public IEnumerator<IFileInfo> GetEnumerator()
+            {
+                var file = new TestFileInfo("@page" + Environment.NewLine + "Original content")
+                {
+                    Name = "UpdateablePage.cshtml"
+                };
+
+                var files = new List<IFileInfo> {  file };
+                return files.GetEnumerator();
+            }
+
+            IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+        }
     }
 }