Added logging for precompiled views in RazorViewEngine

Addresses #5462

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

@@ -59,7 +59,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 
             foreach (var item in views)
             {
-                var cacheEntry = new CompilerCacheResult(item.Key, new CompilationResult(item.Value));
+                var cacheEntry = new CompilerCacheResult(item.Key, new CompilationResult(item.Value), isPrecompiled: true);
                 _cache.Set(GetNormalizedPath(item.Key), Task.FromResult(cacheEntry));
             }
         }

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

@@ -27,6 +27,19 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
         {
         }
 
+        /// <summary>
+        /// Initializes a new instance of <see cref="CompilerCacheResult"/> with the specified
+        /// <see cref="Compilation.CompilationResult"/>.
+        /// </summary>
+        /// <param name="relativePath">Path of the view file relative to the application base.</param>
+        /// <param name="compilationResult">The <see cref="Compilation.CompilationResult"/>.</param>
+        /// <param name="isPrecompiled"><c>true</c> if the view is precompiled, <c>false</c> otherwise.</param>
+        public CompilerCacheResult(string relativePath, CompilationResult compilationResult, bool isPrecompiled)
+            : this(relativePath, compilationResult, EmptyArray<IChangeToken>.Instance)
+        {
+            IsPrecompiled = isPrecompiled;
+        }
+
         /// <summary>
         /// Initializes a new instance of <see cref="CompilerCacheResult"/> with the specified
         /// <see cref="Compilation.CompilationResult"/>.
@@ -51,9 +64,10 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 
             var propertyBindExpression = Expression.Bind(pathProperty, Expression.Constant(relativePath));
             var objectInitializeExpression = Expression.MemberInit(newExpression, propertyBindExpression);
-            PageFactory =  Expression
+            PageFactory = Expression
                 .Lambda<Func<IRazorPage>>(objectInitializeExpression)
                 .Compile();
+            IsPrecompiled = false;
         }
 
         /// <summary>
@@ -71,6 +85,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 
             ExpirationTokens = expirationTokens;
             PageFactory = null;
+            IsPrecompiled = false;
         }
 
         /// <summary>
@@ -87,5 +102,10 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
         /// Gets a delegate that creates an instance of the <see cref="IRazorPage"/>.
         /// </summary>
         public Func<IRazorPage> PageFactory { get; }
+
+        /// <summary>
+        /// Gets a value that determines if the view is precompiled.
+        /// </summary>
+        public bool IsPrecompiled { get; }
     }
 }

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

@@ -62,7 +62,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             var result = CompilerCache.GetOrAdd(relativePath, _compileDelegate);
             if (result.Success)
             {
-                return new RazorPageFactoryResult(result.PageFactory, result.ExpirationTokens);
+                return new RazorPageFactoryResult(result.PageFactory, result.ExpirationTokens, result.IsPrecompiled);
             }
             else
             {

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

@@ -19,6 +19,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 
         private static readonly Action<ILogger, string, string, Exception> _viewLookupCacheMiss;
         private static readonly Action<ILogger, string, string, Exception> _viewLookupCacheHit;
+        private static readonly Action<ILogger, string, Exception> _precompiledViewFound;
 
         static MvcRazorLoggerExtensions()
         {
@@ -42,6 +43,11 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
                 2,
                 "View lookup cache hit for view '{ViewName}' in controller '{ControllerName}'.");
 
+            _precompiledViewFound = LoggerMessage.Define<string>(
+                LogLevel.Debug,
+                3,
+                "Using precompiled view for '{RelativePath}'.");
+
             _generatedCodeToAssemblyCompilationStart = LoggerMessage.Define<string>(
                 LogLevel.Debug,
                 1,
@@ -79,6 +85,11 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             _viewLookupCacheHit(logger, viewName, controllerName, null);
         }
 
+        public static void PrecompiledViewFound(this ILogger logger, string relativePath)
+        {
+            _precompiledViewFound(logger, relativePath, null);
+        }
+
         public static void GeneratedCodeToAssemblyCompilationStart(this ILogger logger, string filePath)
         {
             _generatedCodeToAssemblyCompilationStart(logger, filePath, null);

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

@@ -26,6 +26,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
 
             ExpirationTokens = expirationTokens;
             RazorPageFactory = null;
+            IsPrecompiled = false;
         }
 
         /// <summary>
@@ -37,6 +38,21 @@ namespace Microsoft.AspNetCore.Mvc.Razor
         public RazorPageFactoryResult(
             Func<IRazorPage> razorPageFactory,
             IList<IChangeToken> expirationTokens)
+            : this(razorPageFactory, expirationTokens, isPrecompiled: false)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of <see cref="RazorPageFactoryResult"/> with the
+        /// specified <see cref="IRazorPage"/> factory.
+        /// </summary>
+        /// <param name="razorPageFactory">The <see cref="IRazorPage"/> factory.</param>
+        /// <param name="expirationTokens">One or more <see cref="IChangeToken"/> instances.</param>
+        /// <param name="isPrecompiled"><c>true</c> if the view is precompiled, <c>false</c> otherwise.</param>
+        public RazorPageFactoryResult(
+            Func<IRazorPage> razorPageFactory,
+            IList<IChangeToken> expirationTokens,
+            bool isPrecompiled)
         {
             if (razorPageFactory == null)
             {
@@ -50,6 +66,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
 
             RazorPageFactory = razorPageFactory;
             ExpirationTokens = expirationTokens;
+            IsPrecompiled = isPrecompiled;
         }
 
         /// <summary>
@@ -68,5 +85,10 @@ namespace Microsoft.AspNetCore.Mvc.Razor
         /// Gets a value that determines if the page was successfully located.
         /// </summary>
         public bool Success => RazorPageFactory != null;
+
+        /// <summary>
+        /// Gets a value that determines if the view is precompiled.
+        /// </summary>
+        public bool IsPrecompiled { get; }
     }
 }

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

@@ -395,7 +395,8 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             return ViewLookupCache.Set<ViewLocationCacheResult>(cacheKey, cacheResult, cacheEntryOptions);
         }
 
-        private ViewLocationCacheResult CreateCacheResult(
+        // Internal for unit testing
+        internal ViewLocationCacheResult CreateCacheResult(
             HashSet<IChangeToken> expirationTokens,
             string relativePath,
             bool isMainPage)
@@ -415,6 +416,10 @@ namespace Microsoft.AspNetCore.Mvc.Razor
                 var viewStartPages = isMainPage ?
                     GetViewStartPages(relativePath, expirationTokens) :
                     EmptyArray<ViewLocationCacheItem>.Instance;
+                if (factoryResult.IsPrecompiled)
+                {
+                    _logger.PrecompiledViewFound(relativePath);
+                }
 
                 return new ViewLocationCacheResult(
                     new ViewLocationCacheItem(factoryResult.RazorPageFactory, relativePath),

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

@@ -241,6 +241,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 
             // Assert
             Assert.True(result.Success);
+            Assert.True(result.IsPrecompiled);
             Assert.IsType<PreCompile>(result.PageFactory());
         }
 

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

@@ -1283,6 +1283,35 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Test
             Assert.Equal(expected, result.SearchedLocations);
         }
 
+        [Fact]
+        public void CreateCacheResult_LogsPrecompiledViewFound()
+        {
+            // Arrange
+            var sink = new TestSink();
+            var loggerFactory = new TestLoggerFactory(sink, enabled: true);
+
+            var relativePath = "/Views/Foo/details.cshtml";
+            var pageFactory = new Mock<IRazorPageFactoryProvider>();
+            pageFactory
+                .Setup(p => p.CreateFactory(relativePath))
+                .Returns(new RazorPageFactoryResult(() => Mock.Of<IRazorPage>(), new IChangeToken[0], isPrecompiled: true))
+                .Verifiable();
+
+            var viewEngine = new RazorViewEngine(
+                pageFactory.Object,
+                Mock.Of<IRazorPageActivator>(),
+                new HtmlTestEncoder(),
+                GetOptionsAccessor(expanders: null),
+                loggerFactory);
+
+            // Act
+            var result = viewEngine.CreateCacheResult(null, relativePath, false);
+
+            // Assert
+            var logMessage = Assert.Single(sink.Writes);
+            Assert.Equal($"Using precompiled view for '{relativePath}'.", logMessage.State.ToString());
+        }
+
         [Theory]
         [InlineData("/Test-View.cshtml")]
         [InlineData("~/Test-View.CSHTML")]