Allow serving Razor files with leading underscore

Fixes https://github.com/aspnet/Mvc/issues/8617

src/Microsoft.AspNetCore.Mvc.RazorPages/Internal/RazorProjectPageRouteModelProvider.cs

@@ -57,11 +57,6 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
         {
             foreach (var item in _razorFileSystem.EnumerateItems(_pagesOptions.RootDirectory))
             {
-                if (!IsRouteable(item))
-                {
-                    continue;
-                }
-
                 var relativePath = item.CombinedPath;
                 if (context.RouteModels.Any(m => string.Equals(relativePath, m.RelativePath, StringComparison.OrdinalIgnoreCase)))
                 {
@@ -99,11 +94,6 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
         {
             foreach (var item in _razorFileSystem.EnumerateItems(AreaRootDirectory))
             {
-                if (!IsRouteable(item))
-                {
-                    continue;
-                }
-
                 var relativePath = item.CombinedPath;
                 if (context.RouteModels.Any(m => string.Equals(relativePath, m.RelativePath, StringComparison.OrdinalIgnoreCase)))
                 {
@@ -125,11 +115,5 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 }
             }
         }
-
-        private static bool IsRouteable(RazorProjectItem item)
-        {
-            // Pages like _ViewImports should not be routeable.
-            return !item.FileName.StartsWith("_", StringComparison.OrdinalIgnoreCase);
-        }
     }
 }

test/Microsoft.AspNetCore.Mvc.RazorPages.Test/Internal/CompiledPageRouteModelProviderTest.cs

@@ -6,7 +6,6 @@ using System.Collections.Generic;
 using System.Linq;
 using Microsoft.AspNetCore.Mvc.ApplicationModels;
 using Microsoft.AspNetCore.Mvc.ApplicationParts;
-using Microsoft.AspNetCore.Mvc.Razor;
 using Microsoft.AspNetCore.Mvc.Razor.Compilation;
 using Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure;
 using Microsoft.AspNetCore.Razor.Hosting;
@@ -563,6 +562,57 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 });
         }
 
+        [Fact]
+        public void OnProvidersExecuting_AllowsRazorFilesWithUnderscorePrefix()
+        {
+            // Arrange
+            var descriptors = new[]
+            {
+                CreateVersion_2_1_Descriptor("/Pages/_About.cshtml"),
+                CreateVersion_2_1_Descriptor("/Pages/Home.cshtml"),
+            };
+
+            var provider = CreateProvider(descriptors: descriptors);
+            var context = new PageRouteModelProviderContext();
+
+            // Act
+            provider.OnProvidersExecuting(context);
+
+            // Assert
+            Assert.Collection(
+                context.RouteModels,
+                result =>
+                {
+                    Assert.Equal("/Pages/_About.cshtml", result.RelativePath);
+                    Assert.Equal("/_About", result.ViewEnginePath);
+                    Assert.Collection(
+                        result.Selectors,
+                        selector => Assert.Equal("_About", selector.AttributeRouteModel.Template));
+                    Assert.Collection(
+                        result.RouteValues.OrderBy(k => k.Key),
+                        kvp =>
+                        {
+                            Assert.Equal("page", kvp.Key);
+                            Assert.Equal("/_About", kvp.Value);
+                        });
+                },
+                result =>
+                {
+                    Assert.Equal("/Pages/Home.cshtml", result.RelativePath);
+                    Assert.Equal("/Home", result.ViewEnginePath);
+                    Assert.Collection(
+                        result.Selectors,
+                        selector => Assert.Equal("Home", selector.AttributeRouteModel.Template));
+                    Assert.Collection(
+                        result.RouteValues.OrderBy(k => k.Key),
+                        kvp =>
+                        {
+                            Assert.Equal("page", kvp.Key);
+                            Assert.Equal("/Home", kvp.Value);
+                        });
+                });
+        }
+
         [Fact]
         public void GetRouteTemplate_ReturnsPathFromRazorPageAttribute()
         {

test/Microsoft.AspNetCore.Mvc.RazorPages.Test/Internal/RazorProjectPageRouteModelProviderTest.cs

@@ -53,7 +53,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
             fileSystem.Add(new TestRazorProjectItem("/Areas/Products/Pages/Manage/Categories.cshtml", "@page"));
             fileSystem.Add(new TestRazorProjectItem("/Areas/Products/Pages/Index.cshtml", "@page"));
             fileSystem.Add(new TestRazorProjectItem("/Areas/Products/Pages/List.cshtml", "@page \"{sortOrder?}\""));
-            fileSystem.Add(new TestRazorProjectItem("/Areas/Products/Pages/_ViewStart.cshtml", "@page"));
+            fileSystem.Add(new TestRazorProjectItem("/Areas/Products/Pages/_Test.cshtml", "@page"));
 
             var optionsManager = Options.Create(new RazorPagesOptions { AllowAreas = true });
             var provider = new RazorProjectPageRouteModelProvider(fileSystem, optionsManager, NullLoggerFactory.Instance);
@@ -102,6 +102,24 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                       });
                 },
                 model =>
+                {
+                    Assert.Equal("/Areas/Products/Pages/_Test.cshtml", model.RelativePath);
+                    Assert.Equal("/_Test", model.ViewEnginePath);
+                    Assert.Collection(model.Selectors,
+                        selector => Assert.Equal("Products/_Test", selector.AttributeRouteModel.Template));
+                    Assert.Collection(model.RouteValues.OrderBy(k => k.Key),
+                       kvp =>
+                       {
+                           Assert.Equal("area", kvp.Key);
+                           Assert.Equal("Products", kvp.Value);
+                       },
+                       kvp =>
+                       {
+                           Assert.Equal("page", kvp.Key);
+                           Assert.Equal("/_Test", kvp.Value);
+                       });
+                },
+                model =>
                 {
                     Assert.Equal("/Areas/Products/Pages/Manage/Categories.cshtml", model.RelativePath);
                     Assert.Equal("/Manage/Categories", model.ViewEnginePath);
@@ -272,37 +290,13 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 });
         }
 
-        [Fact]
-        public void OnProvidersExecuting_SkipsPagesStartingWithUnderscore()
-        {
-            // Arrange
-            var fileSystem = new VirtualRazorProjectFileSystem();
-            fileSystem.Add(new TestRazorProjectItem("/Pages/Home.cshtml", "@page"));
-            fileSystem.Add(new TestRazorProjectItem("/Pages/_Layout.cshtml", "@page"));
-
-            var optionsManager = Options.Create(new RazorPagesOptions());
-            optionsManager.Value.RootDirectory = "/";
-            var provider = new RazorProjectPageRouteModelProvider(fileSystem, optionsManager, NullLoggerFactory.Instance);
-            var context = new PageRouteModelProviderContext();
-
-            // Act
-            provider.OnProvidersExecuting(context);
-
-            // Assert
-            Assert.Collection(context.RouteModels,
-                model =>
-                {
-                    Assert.Equal("/Pages/Home.cshtml", model.RelativePath);
-                });
-        }
-
         [Fact]
         public void OnProvidersExecuting_DiscoversFilesUnderBasePath()
         {
             // Arrange
             var fileSystem = new VirtualRazorProjectFileSystem();
             fileSystem.Add(new TestRazorProjectItem("/Pages/Index.cshtml", "@page"));
-            fileSystem.Add(new TestRazorProjectItem("/Pages/_Layout.cshtml", "@page"));
+            fileSystem.Add(new TestRazorProjectItem("/Pages/_Layout.cshtml", ""));
             fileSystem.Add(new TestRazorProjectItem("/NotPages/Index.cshtml", "@page"));
             fileSystem.Add(new TestRazorProjectItem("/NotPages/_Layout.cshtml", "@page"));
             fileSystem.Add(new TestRazorProjectItem("/Index.cshtml", "@page"));