Allow returning precompiled views without sources

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

@@ -120,7 +120,14 @@ private GetOrAddResult GetOrAddCore(string relativePath,
                 var fileInfo = _fileProvider.GetFileInfo(relativePath);
                 if (!fileInfo.Exists)
                 {
-                    return null;
+                    // Assigning to IsValidatedPreCompiled is an atomic operation and will result in a safe race
+                    // if it is being concurrently updated and read.
+                    cacheEntry.IsValidatedPreCompiled = true;
+                    return new GetOrAddResult
+                    {
+                        CompilationResult = CompilationResult.Successful(cacheEntry.CompiledType),
+                        CompilerCacheEntry = cacheEntry
+                    };
                 }
 
                 var relativeFileInfo = new RelativeFileInfo(fileInfo, relativePath);

test/Microsoft.AspNet.Mvc.FunctionalTests/PrecompilationTest.cs

@@ -162,6 +162,57 @@ public async Task PrecompiledView_RendersCorrectly()
                 File.WriteAllText(Path.Combine(viewsDirectory, "_GlobalImport.cshtml"), globalContent.TrimEnd(' '));
             }
         }
+
+        [Fact]
+        public async Task PrecompiledView_RendersWithoutSourceFile()
+        {
+            // Arrange
+            IServiceCollection serviceCollection = null;
+            var server = TestHelper.CreateServer(_app, SiteName, services =>
+            {
+                _configureServices(services);
+                serviceCollection = services;
+            });
+            var client = server.CreateClient();
+
+            var serviceProvider = serviceCollection.BuildServiceProvider();
+            var applicationEnvironment = serviceProvider.GetRequiredService<IApplicationEnvironment>();
+
+            var viewsDirectory = Path.Combine(applicationEnvironment.ApplicationBasePath, "Views", "Home");
+            var layoutContent = File.ReadAllText(Path.Combine(viewsDirectory, "Layout.cshtml"));
+            var indexContent = File.ReadAllText(Path.Combine(viewsDirectory, "Index.cshtml"));
+            var viewstartContent = File.ReadAllText(Path.Combine(viewsDirectory, "_ViewStart.cshtml"));
+            var globalContent = File.ReadAllText(Path.Combine(viewsDirectory, "_GlobalImport.cshtml"));
+
+            // We will render a view that writes the fully qualified name of the Assembly containing the type of
+            // the view. If the view is precompiled, this assembly will be PrecompilationWebsite.
+            var assemblyNamePrefix = GetAssemblyNamePrefix();
+
+            try
+            {
+                // Act
+                await DeleteFile(viewsDirectory, "_ViewStart.cshtml");
+                await DeleteFile(viewsDirectory, "_Layout.cshtml");
+                await DeleteFile(viewsDirectory, "Index.cshtml");
+
+                var response = await client.GetAsync("http://localhost/Home/Index");
+                var responseContent = await response.Content.ReadAsStringAsync();
+
+                // Assert
+                Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+                var parsedResponse1 = new ParsedResponse(responseContent);
+                Assert.StartsWith(assemblyNamePrefix, parsedResponse1.ViewStart);
+                Assert.StartsWith(assemblyNamePrefix, parsedResponse1.Layout);
+                Assert.StartsWith(assemblyNamePrefix, parsedResponse1.Index);
+            }
+            finally
+            {
+                File.WriteAllText(Path.Combine(viewsDirectory, "Layout.cshtml"), layoutContent.TrimEnd(' '));
+                File.WriteAllText(Path.Combine(viewsDirectory, "Index.cshtml"), indexContent.TrimEnd(' '));
+                File.WriteAllText(Path.Combine(viewsDirectory, "_ViewStart.cshtml"), viewstartContent.TrimEnd(' '));
+                File.WriteAllText(Path.Combine(viewsDirectory, "_GlobalImport.cshtml"), globalContent.TrimEnd(' '));
+            }
+        }
 
         [Fact]
         public async Task PrecompiledView_UsesCompilationOptionsFromApplication()
@@ -284,6 +335,17 @@ private static async Task<string> TouchFile(string viewsDir, string file)
 
             return path;
         }
+
+        private static async Task<string> DeleteFile(string viewsDir, string file)
+        {
+            var path = Path.Combine(viewsDir, file);
+            File.Delete(path);
+
+            // Delay to allow the file system watcher to catch up.
+            await Task.Delay(_cacheDelayInterval);
+
+            return path;
+        }
 
         private sealed class ParsedResponse
         {

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

@@ -293,7 +293,7 @@ public void GetOrAdd_UsesValueFromCache_IfGlobalHasNotChanged()
         }
 
         [Fact]
-        public void GetOrAdd_ReturnsFileNotFoundResult_IfPrecompiledViewWasRemovedFromFileSystem()
+        public void GetOrAdd_ReturnsPrecompiledView_IfPrecompiledViewWasRemovedFromFileSystem()
         {
             // Arrange
             var precompiledViews = new ViewCollection();
@@ -305,8 +305,8 @@ public void GetOrAdd_ReturnsFileNotFoundResult_IfPrecompiledViewWasRemovedFromFi
                                         compile: _ => { throw new Exception("shouldn't be invoked"); });
 
             // Assert
-            Assert.Same(CompilerCacheResult.FileNotFound, result);
-            Assert.Null(result.CompilationResult);
+            Assert.NotSame(CompilerCacheResult.FileNotFound, result);
+            Assert.NotNull(result.CompilationResult);
         }
 
         [Fact]