Replaced an unintended NullReferenceException when a partial view could not be located and introduced a ViewNotFoundException instead

Conflicts:
	src/Nancy.Tests.Functional/Tests/PartialViewTests.cs
	src/Nancy.ViewEngines.Razor/HtmlHelpers.cs

Author: dwonisch

src/Nancy.Tests.Functional/Modules/RazorTestModule.cs

@@ -24,6 +24,13 @@ public RazorTestModule()
 
                 return serialized;
             };
+
+            Get["/razor-partialnotfound"] = _ =>
+            {
+                this.ViewBag.Name = "Bob";
+
+                return View["RazorPageWithUnknownPartial"];
+            };
         }
     }
 }

src/Nancy.Tests.Functional/Nancy.Tests.Functional.csproj

@@ -155,6 +155,9 @@
   </ItemGroup>
   <ItemGroup>
     <None Include="packages.config" />
+    <None Include="Views\RazorPageWithUnknownPartial.cshtml">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
     <None Include="Views\_PartialTest.cshtml">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>

src/Nancy.Tests.Functional/Tests/PartialViewTests.cs

@@ -1,9 +1,10 @@
 namespace Nancy.Tests.Functional.Tests
 {
     using System;
-    using Bootstrapper;
-    using Modules;
-    using Testing;
+    using Nancy.Bootstrapper;
+    using Nancy.Testing;
+    using Nancy.Tests.Functional.Modules;
+    using Nancy.ViewEngines;
     using Xunit;
 
     public class PartialViewTests
@@ -41,5 +42,16 @@ public void When_Using_Partial_View_Then_First_Index_Of_ViewStart_Should_Equal_L
             // If the index is not the same then the string occurs twice...
             Assert.Equal(firstIndex, lastIndex);
         }
+
+        [Fact]
+        public void When_Partial_View_Could_Not_Be_Found_An_Meaningful_Exception_Should_Be_Thrown()
+        {
+            Assert.Throws<ViewNotFoundException>(() =>
+            {
+                var response = this.browser.Get(@"/razor-partialnotfound");
+
+                response.Body.AsString();
+            });
+        }
     }
 }

src/Nancy.Tests.Functional/Views/RazorPageWithUnknownPartial.cshtml

@@ -0,0 +1,5 @@
+@inherits Nancy.ViewEngines.Razor.NancyRazorViewBase<dynamic>
+
+Hello @ViewBag.Name
+
+@Html.Partial("_UnknownPartialTest.cshtml")

src/Nancy.ViewEngines.Razor/HtmlHelpers.cs

@@ -2,7 +2,8 @@
 {
     using System;
     using System.IO;
-    using Nancy.Security;
+    using System.Linq;
+    using System.Security.Claims;
 
     /// <summary>
     /// Helpers to generate html content.
@@ -76,6 +77,10 @@ public IHtmlString Partial(string viewName, dynamic modelForPartial)
         {
             var view = this.RenderContext.LocateView(viewName, modelForPartial);
 
+            if (view == null) {
+                throw new ViewNotFoundException(viewName, Engine.Extensions.ToArray());
+            }
+
             var response = this.Engine.RenderView(view, modelForPartial, this.RenderContext, true);
             Action<Stream> action = response.Contents;
             var mem = new MemoryStream();

src/Nancy/ViewEngines/ViewNotFoundException.cs

@@ -39,6 +39,23 @@ public ViewNotFoundException(string viewName, string[] availableViewEngineExtens
                     Environment.NewLine);
         }
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ViewNotFoundException"/>.
+        /// </summary>
+        /// <param name="viewName">The name of the view that was being located.</param>
+        /// <param name="availableViewEngineExtensions">List of available view extensions that can be rendered by the available view engines.</param>
+        public ViewNotFoundException(string viewName, string[] availableViewEngineExtensions)
+        {
+            this.ViewName = viewName;
+            this.AvailableViewEngineExtensions = availableViewEngineExtensions;
+
+            this.message = String.Format(
+                    "Unable to locate view '{0}'{2}Currently available view engine extensions: {1}{2}",
+                    this.ViewName,
+                    string.Join(",", this.AvailableViewEngineExtensions),
+                    Environment.NewLine);
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="ViewNotFoundException"/>
         /// </summary>