From 9fe480f73524d6cd0024af679efff4adf8ae4080 Mon Sep 17 00:00:00 2001
From: Pranav K <prkrishn@hotmail.com>
Date: Wed, 19 Apr 2017 16:09:03 -0700
Subject: [PATCH] Add LazyReferenceMetadataFeature

---
 .../MvcRazorMvcCoreBuilderExtensions.cs       |  9 ++----
 .../Internal/LazyMetadataReferenceFeature.cs  | 28 +++++++++++++++++++
 .../Internal/RazorReferenceManager.cs         |  9 +++---
 3 files changed, 36 insertions(+), 10 deletions(-)
 create mode 100644 src/Microsoft.AspNetCore.Mvc.Razor/Internal/LazyMetadataReferenceFeature.cs

diff --git a/src/Microsoft.AspNetCore.Mvc.Razor/DependencyInjection/MvcRazorMvcCoreBuilderExtensions.cs b/src/Microsoft.AspNetCore.Mvc.Razor/DependencyInjection/MvcRazorMvcCoreBuilderExtensions.cs
index c7875c3b22..27a255d387 100644
--- a/src/Microsoft.AspNetCore.Mvc.Razor/DependencyInjection/MvcRazorMvcCoreBuilderExtensions.cs
+++ b/src/Microsoft.AspNetCore.Mvc.Razor/DependencyInjection/MvcRazorMvcCoreBuilderExtensions.cs
@@ -155,13 +155,13 @@ namespace Microsoft.Extensions.DependencyInjection
             // creating the singleton RazorViewEngine instance.
             services.TryAddTransient<IRazorPageFactoryProvider, DefaultRazorPageFactoryProvider>();
 
-
             //
             // Razor compilation infrastructure
             //
             services.TryAddSingleton<RazorProject, DefaultRazorProject>();
             services.TryAddSingleton<RazorTemplateEngine, MvcRazorTemplateEngine>();
             services.TryAddSingleton<RazorCompiler>();
+            services.TryAddSingleton<LazyMetadataReferenceFeature>();
 
             services.TryAddSingleton<RazorEngine>(s =>
             {
@@ -171,11 +171,8 @@ namespace Microsoft.Extensions.DependencyInjection
 
                     b.Features.Add(new Microsoft.CodeAnalysis.Razor.DefaultTagHelperFeature());
 
-                    var referenceManager = s.GetRequiredService<RazorReferenceManager>();
-                    b.Features.Add(new Microsoft.CodeAnalysis.Razor.DefaultMetadataReferenceFeature()
-                    {
-                        References = referenceManager.CompilationReferences.ToArray(),
-                    });
+                    var metadataReferenceFeature = s.GetRequiredService<LazyMetadataReferenceFeature>();
+                    b.Features.Add(metadataReferenceFeature);
                 });
             });
 
diff --git a/src/Microsoft.AspNetCore.Mvc.Razor/Internal/LazyMetadataReferenceFeature.cs b/src/Microsoft.AspNetCore.Mvc.Razor/Internal/LazyMetadataReferenceFeature.cs
new file mode 100644
index 0000000000..c9c040a812
--- /dev/null
+++ b/src/Microsoft.AspNetCore.Mvc.Razor/Internal/LazyMetadataReferenceFeature.cs
@@ -0,0 +1,28 @@
+// 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.Collections.Generic;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Razor;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.Internal
+{
+    public class LazyMetadataReferenceFeature : IMetadataReferenceFeature
+    {
+        private readonly RazorReferenceManager _referenceManager;
+
+        public LazyMetadataReferenceFeature(RazorReferenceManager referenceManager)
+        {
+            _referenceManager = referenceManager;
+        }
+
+        /// <remarks>
+        /// Invoking <see cref="RazorReferenceManager.CompilationReferences"/> ensures that compilation
+        /// references are lazily evaluated.
+        /// </remarks>
+        public IReadOnlyList<MetadataReference> References => _referenceManager.CompilationReferences;
+
+        public RazorEngine Engine { get; set; }
+    }
+}
diff --git a/src/Microsoft.AspNetCore.Mvc.Razor/Internal/RazorReferenceManager.cs b/src/Microsoft.AspNetCore.Mvc.Razor/Internal/RazorReferenceManager.cs
index 2e21de7705..4d5338ae5e 100644
--- a/src/Microsoft.AspNetCore.Mvc.Razor/Internal/RazorReferenceManager.cs
+++ b/src/Microsoft.AspNetCore.Mvc.Razor/Internal/RazorReferenceManager.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.Collections.Generic;
+using System.Linq;
 using System.Threading;
 using Microsoft.AspNetCore.Mvc.ApplicationParts;
 using Microsoft.AspNetCore.Mvc.Razor.Compilation;
@@ -16,7 +17,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
         private readonly IList<MetadataReference> _additionalMetadataReferences;
         private object _compilationReferencesLock = new object();
         private bool _compilationReferencesInitialized;
-        private IList<MetadataReference> _compilationReferences;
+        private IReadOnlyList<MetadataReference> _compilationReferences;
 
         public RazorReferenceManager(
             ApplicationPartManager partManager,
@@ -26,7 +27,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             _additionalMetadataReferences = optionsAccessor.Value.AdditionalCompilationReferences;
         }
 
-        public IList<MetadataReference> CompilationReferences
+        public IReadOnlyList<MetadataReference> CompilationReferences
         {
             get
             {
@@ -38,7 +39,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             }
         }
 
-        private IList<MetadataReference> GetCompilationReferences()
+        private IReadOnlyList<MetadataReference> GetCompilationReferences()
         {
             var feature = new MetadataReferenceFeature();
             _partManager.PopulateFeature(feature);
@@ -46,7 +47,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 
             if (_additionalMetadataReferences.Count == 0)
             {
-                return applicationReferences;
+                return applicationReferences.ToArray();
             }
 
             var compilationReferences = new List<MetadataReference>(applicationReferences.Count + _additionalMetadataReferences.Count);