Do not re-discover runtime compiled RazorPage files for precompiled Razor Pages.

Fixes #6718

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

@@ -9,7 +9,6 @@ using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.Razor;
 using Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure;
 using Microsoft.Extensions.Internal;
-using Microsoft.Extensions.Options;
 
 namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
 {

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

@@ -1,6 +1,7 @@
 // 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;
 using Microsoft.AspNetCore.Mvc.ApplicationModels;
 using Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure;
 using Microsoft.AspNetCore.Razor.Language;
@@ -25,7 +26,10 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
             _logger = loggerFactory.CreateLogger<RazorProjectPageRouteModelProvider>();
         }
         
-        public int Order => -1000;
+        /// <remarks>
+        /// Ordered to execute after <see cref="CompiledPageRouteModelProvider"/>.
+        /// </remarks>
+        public int Order => -1000 + 10; 
 
         public void OnProvidersExecuted(PageRouteModelProviderContext context)
         {
@@ -47,6 +51,13 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                     continue;
                 }
 
+                if (IsAlreadyRegistered(context, item))
+                {
+                    // The CompiledPageRouteModelProvider (or another provider) already registered a PageRoute for this path.
+                    // Don't register a duplicate entry for this route.
+                    continue;
+                }
+
                 var routeModel = new PageRouteModel(
                     relativePath: item.CombinedPath,
                     viewEnginePath: item.FilePathWithoutExtension);
@@ -55,5 +66,20 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 context.RouteModels.Add(routeModel);
             }
         }
+
+        private bool IsAlreadyRegistered(PageRouteModelProviderContext context, RazorProjectItem projectItem)
+        {
+            for (var i = 0; i < context.RouteModels.Count; i++)
+            {
+                var routeModel = context.RouteModels[i];
+                if (string.Equals(routeModel.ViewEnginePath, projectItem.FilePathWithoutExtension, StringComparison.OrdinalIgnoreCase) &&
+                    string.Equals(routeModel.RelativePath, projectItem.CombinedPath, StringComparison.OrdinalIgnoreCase))
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
     }
 }

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

@@ -176,5 +176,40 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                     Assert.Equal("/Pages/Index.cshtml", model.RelativePath);
                 });
         }
+
+        [Fact]
+        public void OnProvidersExecuting_DoesNotAddPageDirectivesIfItAlreadyExists()
+        {
+            // Arrange
+            var fileProvider = new TestFileProvider();
+            var file1 = fileProvider.AddFile("/Pages/Home.cshtml", "@page");
+            var file2 = fileProvider.AddFile("/Pages/Test.cshtml", "@page");
+
+            var dir1 = fileProvider.AddDirectoryContent("/Pages", new IFileInfo[] { file1, file2 });
+            fileProvider.AddDirectoryContent("/", new[] { dir1 });
+
+            var project = new TestRazorProject(fileProvider);
+
+            var optionsManager = new TestOptionsManager<RazorPagesOptions>();
+            optionsManager.Value.RootDirectory = "/";
+            var provider = new RazorProjectPageRouteModelProvider(project, optionsManager, NullLoggerFactory.Instance);
+            var context = new PageRouteModelProviderContext();
+            var pageModel = new PageRouteModel("/Pages/Test.cshtml", "/Pages/Test");
+            context.RouteModels.Add(pageModel);
+
+            // Act
+            provider.OnProvidersExecuting(context);
+
+            // Assert
+            Assert.Collection(context.RouteModels,
+                model => Assert.Same(pageModel, model),
+                model =>
+                {
+                    Assert.Equal("/Pages/Home.cshtml", model.RelativePath);
+                    Assert.Equal("/Pages/Home", model.ViewEnginePath);
+                    Assert.Collection(model.Selectors,
+                        selector => Assert.Equal("Pages/Home", selector.AttributeRouteModel.Template));
+                });
+        }
     }
 }