Improve ViewLocalizer resource look-up semantics:

- Always prepend with application name and let underlying `IStringLocalizerFactory` do the name gymnastics
- Use ExecutingFilePath instead of view name
- Trim off the file extension (so your resource doesn't have to have ".cshtml" in its name)
- Improved doc comments
- Added tests to cover ViewLocalizer behavior
- #3718
- #2767

src/Microsoft.AspNet.Mvc.Localization/IViewLocalizer.cs

@@ -4,7 +4,7 @@
 namespace Microsoft.AspNet.Mvc.Localization
 {
     /// <summary>
-    /// A service that provides localized strings for views.
+    /// Represents a type that provides HTML-aware localization for views.
     /// </summary>
     public interface IViewLocalizer : IHtmlLocalizer
     {

src/Microsoft.AspNet.Mvc.Localization/ViewLocalizer.cs

@@ -3,7 +3,9 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Globalization;
+using System.IO;
 using Microsoft.AspNet.Mvc.Rendering;
 using Microsoft.AspNet.Mvc.ViewFeatures.Internal;
 using Microsoft.Extensions.Localization;
@@ -12,7 +14,8 @@ using Microsoft.Extensions.PlatformAbstractions;
 namespace Microsoft.AspNet.Mvc.Localization
 {
     /// <summary>
-    /// A <see cref="IHtmlLocalizer"/> implementation that provides localized strings for views.
+    /// An <see cref="IViewLocalizer"/> implementation that derives the resource location from the executing view's
+    /// file path.
     /// </summary>
     public class ViewLocalizer : IViewLocalizer, ICanHasViewContext
     {
@@ -93,12 +96,30 @@ namespace Microsoft.AspNet.Mvc.Localization
                 throw new ArgumentNullException(nameof(viewContext));
             }
 
-            var baseName = viewContext.View.Path.Replace('/', '.').Replace('\\', '.');
-            if (baseName.StartsWith(".", StringComparison.OrdinalIgnoreCase))
+            // Given a view path "/Views/Home/Index.cshtml" we want a baseName like "MyApplication.Views.Home.Index"
+
+            var path = viewContext.ExecutingFilePath;
+
+            if (string.IsNullOrEmpty(path))
             {
-                baseName = baseName.Substring(1);
+                path = viewContext.View.Path;
             }
 
+            // Trim the file extension from the end of the path
+            if (!string.IsNullOrEmpty(path) && Path.HasExtension(path))
+            {
+                var extension = Path.GetExtension(path);
+                path = path.Substring(0, path.Length - extension.Length);
+            }
+
+            Debug.Assert(!string.IsNullOrEmpty(path), "Couldn't determine a path for the view");
+
+            var baseName = path.Replace('/', '.').Replace('\\', '.');
+            baseName = baseName.TrimStart('.');
+
+            // Prepend the application name
+            baseName = _applicationName + "." + baseName;
+
             _localizer = _localizerFactory.Create(baseName, _applicationName);
         }
     }

test/Microsoft.AspNet.Mvc.Localization.Test/ViewLocalizerTest.cs

@@ -16,6 +16,39 @@ namespace Microsoft.AspNet.Mvc.Localization.Test
 {
     public class ViewLocalizerTest
     {
+        [Theory]
+        [InlineData("TestApplication", "Views/Home/Index.cshtml", "Views/Home/Index.cshtml", "TestApplication.Views.Home.Index")]
+        [InlineData("TestApplication.Web", "Views/Home/Index.cshtml", "Views/Home/Index.cshtml", "TestApplication.Web.Views.Home.Index")]
+        [InlineData("TestApplication", "Views/Home/Index.cshtml", "Views/Shared/_Layout.cshtml", "TestApplication.Views.Shared._Layout")]
+        [InlineData("TestApplication", "Views/Home/Index.cshtml", "Views/Shared/_MyPartial.cshtml", "TestApplication.Views.Shared._MyPartial")]
+        [InlineData("TestApplication", "Views/Home/Index.cshtml", "Views/Home/_HomePartial.cshtml", "TestApplication.Views.Home._HomePartial")]
+        [InlineData("TestApplication", "Views/Home/Index.cshtml", null, "TestApplication.Views.Home.Index")]
+        [InlineData("TestApplication", "Views/Home/Index.txt", null, "TestApplication.Views.Home.Index")]
+        [InlineData("TestApplication", "Views/Home/Index.cshtml", "", "TestApplication.Views.Home.Index")]
+        [InlineData("TestApplication", "Views/Home/Index.txt", "", "TestApplication.Views.Home.Index")]
+        public void ViewLocalizer_LooksForCorrectResourceBaseNameLocation(string appName, string viewPath, string executingPath, string expectedBaseName)
+        {
+            // Arrange
+            var applicationEnvironment = new Mock<IApplicationEnvironment>();
+            applicationEnvironment.Setup(a => a.ApplicationName).Returns(appName);
+            var htmlLocalizerFactory = new Mock<IHtmlLocalizerFactory>(MockBehavior.Loose);
+            var view = new Mock<IView>();
+            view.Setup(v => v.Path).Returns(viewPath);
+            var viewContext = new ViewContext();
+            viewContext.ExecutingFilePath = executingPath;
+            viewContext.View = view.Object;
+            var viewLocalizer = new ViewLocalizer(htmlLocalizerFactory.Object, applicationEnvironment.Object);
+
+            // Act
+            viewLocalizer.Contextualize(viewContext);
+
+            // Assert
+            htmlLocalizerFactory.Verify(h => h.Create(
+                It.Is<string>(baseName => baseName == expectedBaseName),
+                It.Is<string>(location => location == appName)
+            ));
+        }
+
         [Fact]
         public void ViewLocalizer_UseIndexer_ReturnsLocalizedHtmlString()
         {
@@ -29,7 +62,7 @@ namespace Microsoft.AspNet.Mvc.Localization.Test
             htmlLocalizer.Setup(h => h["Hello"]).Returns(localizedString);
 
             var htmlLocalizerFactory = new Mock<IHtmlLocalizerFactory>();
-            htmlLocalizerFactory.Setup(h => h.Create("example", "TestApplication"))
+            htmlLocalizerFactory.Setup(h => h.Create("TestApplication.example", "TestApplication"))
                 .Returns(htmlLocalizer.Object);
 
             var viewLocalizer = new ViewLocalizer(htmlLocalizerFactory.Object, applicationEnvironment.Object);
@@ -62,7 +95,7 @@ namespace Microsoft.AspNet.Mvc.Localization.Test
 
             var htmlLocalizerFactory = new Mock<IHtmlLocalizerFactory>();
             htmlLocalizerFactory.Setup(
-                h => h.Create("example", "TestApplication")).Returns(htmlLocalizer.Object);
+                h => h.Create("TestApplication.example", "TestApplication")).Returns(htmlLocalizer.Object);
 
             var viewLocalizer = new ViewLocalizer(htmlLocalizerFactory.Object, applicationEnvironment.Object);