From 296deea3494941e26fb79c5794ab44fef40bdc0d Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 9 Jul 2025 07:27:12 +0000
Subject: [PATCH 01/10] Initial plan


From 93b15d62694274e90fbad9ebc1d6a03634e9254a Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 9 Jul 2025 07:36:45 +0000
Subject: [PATCH 02/10] Add validation to prevent NotFound and NotFoundPage
 being set simultaneously

Co-authored-by: ilonatommy <32700855+ilonatommy@users.noreply.github.com>
---
 .../Components/src/PublicAPI.Unshipped.txt    |  2 +-
 .../Components/src/Routing/Router.cs          |  7 +-
 .../Components/test/Routing/RouterTest.cs     | 70 +++++++++++++++++++
 3 files changed, 77 insertions(+), 2 deletions(-)

diff --git a/src/Components/Components/src/PublicAPI.Unshipped.txt b/src/Components/Components/src/PublicAPI.Unshipped.txt
index dc07b8afddac..f5e0f10aad7d 100644
--- a/src/Components/Components/src/PublicAPI.Unshipped.txt
+++ b/src/Components/Components/src/PublicAPI.Unshipped.txt
@@ -1,7 +1,7 @@
 #nullable enable
 *REMOVED*Microsoft.AspNetCore.Components.ResourceAsset.ResourceAsset(string! url, System.Collections.Generic.IReadOnlyList<Microsoft.AspNetCore.Components.ResourceAssetProperty!>? properties) -> void
 Microsoft.AspNetCore.Components.ResourceAsset.ResourceAsset(string! url, System.Collections.Generic.IReadOnlyList<Microsoft.AspNetCore.Components.ResourceAssetProperty!>? properties = null) -> void
-Microsoft.AspNetCore.Components.Routing.Router.NotFoundPage.get -> System.Type!
+Microsoft.AspNetCore.Components.Routing.Router.NotFoundPage.get -> System.Type?
 Microsoft.AspNetCore.Components.Routing.Router.NotFoundPage.set -> void
 Microsoft.AspNetCore.Components.Infrastructure.ComponentsMetricsServiceCollectionExtensions
 Microsoft.AspNetCore.Components.NavigationManager.OnNotFound -> System.EventHandler<Microsoft.AspNetCore.Components.Routing.NotFoundEventArgs!>!
diff --git a/src/Components/Components/src/Routing/Router.cs b/src/Components/Components/src/Routing/Router.cs
index eedff373f656..79a48ec9f973 100644
--- a/src/Components/Components/src/Routing/Router.cs
+++ b/src/Components/Components/src/Routing/Router.cs
@@ -77,7 +77,7 @@ static readonly IReadOnlyDictionary<string, object> _emptyParametersDictionary
     /// </summary>
     [Parameter]
     [DynamicallyAccessedMembers(LinkerFlags.Component)]
-    public Type NotFoundPage { get; set; } = default!;
+    public Type? NotFoundPage { get; set; }
 
     /// <summary>
     /// Gets or sets the content to display when a match is found for the requested route.
@@ -141,6 +141,11 @@ public async Task SetParametersAsync(ParameterView parameters)
             throw new InvalidOperationException($"The {nameof(Router)} component requires a value for the parameter {nameof(Found)}.");
         }
 
+        if (NotFound != null && NotFoundPage != null)
+        {
+            throw new InvalidOperationException($"The {nameof(Router)} component cannot have both {nameof(NotFound)} and {nameof(NotFoundPage)} parameters set. Use either {nameof(NotFound)} render fragment or {nameof(NotFoundPage)} component type, but not both.");
+        }
+
         if (NotFoundPage != null)
         {
             if (!typeof(IComponent).IsAssignableFrom(NotFoundPage))
diff --git a/src/Components/Components/test/Routing/RouterTest.cs b/src/Components/Components/test/Routing/RouterTest.cs
index f393a2edccf0..76aece62db60 100644
--- a/src/Components/Components/test/Routing/RouterTest.cs
+++ b/src/Components/Components/test/Routing/RouterTest.cs
@@ -265,6 +265,73 @@ await _renderer.Dispatcher.InvokeAsync(() =>
         Assert.Equal("Not found", renderedFrame.TextContent);
     }
 
+    [Fact]
+    public async Task ThrowsIfBothNotFoundAndNotFoundPageAreSet()
+    {
+        // Arrange
+        var parameters = new Dictionary<string, object>
+        {
+            { nameof(Router.AppAssembly), typeof(RouterTest).Assembly },
+            { nameof(Router.NotFound), (RenderFragment)(builder => builder.AddContent(0, "Custom content")) },
+            { nameof(Router.NotFoundPage), typeof(TestNotFoundPageComponent) },
+        };
+
+        // Act & Assert
+        var exception = await Assert.ThrowsAsync<InvalidOperationException>(async () =>
+            await _renderer.Dispatcher.InvokeAsync(() =>
+                _router.SetParametersAsync(ParameterView.FromDictionary(parameters))));
+
+        Assert.Contains("cannot have both NotFound and NotFoundPage parameters set", exception.Message);
+    }
+
+    [Fact]
+    public async Task UsesNotFoundPageIfSpecified()
+    {
+        // Arrange
+        _navigationManager.NotifyLocationChanged("https://www.example.com/subdir/nonexistent", false);
+        var parameters = new Dictionary<string, object>
+        {
+            { nameof(Router.AppAssembly), typeof(RouterTest).Assembly },
+            { nameof(Router.NotFoundPage), typeof(TestNotFoundPageComponent) },
+        };
+
+        // Act
+        await _renderer.Dispatcher.InvokeAsync(() =>
+            _router.SetParametersAsync(ParameterView.FromDictionary(parameters)));
+
+        // Assert
+        var batch = _renderer.Batches.First();
+        var renderedFrame = batch.ReferenceFrames.Skip(1).First(); // Skip the RouteView frame
+        Assert.Equal(RenderTreeFrameType.Attribute, renderedFrame.FrameType);
+        Assert.Equal(nameof(RouteView.RouteData), renderedFrame.AttributeName);
+        var routeData = (RouteData)renderedFrame.AttributeValue;
+        Assert.Equal(typeof(TestNotFoundPageComponent), routeData.PageType);
+    }
+
+    [Fact]
+    public async Task UsesNotFoundPageOverNotFound()
+    {
+        // Arrange - This test verifies that if only NotFoundPage is set (not both), it takes precedence over default
+        _navigationManager.NotifyLocationChanged("https://www.example.com/subdir/nonexistent", false);
+        var parameters = new Dictionary<string, object>
+        {
+            { nameof(Router.AppAssembly), typeof(RouterTest).Assembly },
+            { nameof(Router.NotFoundPage), typeof(TestNotFoundPageComponent) },
+        };
+
+        // Act
+        await _renderer.Dispatcher.InvokeAsync(() =>
+            _router.SetParametersAsync(ParameterView.FromDictionary(parameters)));
+
+        // Assert
+        var batch = _renderer.Batches.First();
+        var renderedFrame = batch.ReferenceFrames.Skip(1).First(); // Skip the RouteView frame
+        Assert.Equal(RenderTreeFrameType.Attribute, renderedFrame.FrameType);
+        Assert.Equal(nameof(RouteView.RouteData), renderedFrame.AttributeName);
+        var routeData = (RouteData)renderedFrame.AttributeValue;
+        Assert.Equal(typeof(TestNotFoundPageComponent), routeData.PageType);
+    }
+
     internal class TestNavigationManager : NavigationManager
     {
         public TestNavigationManager() =>
@@ -306,4 +373,7 @@ public class MatchAnythingComponent : ComponentBase { }
 
     [Route("a/b/c")]
     public class MultiSegmentRouteComponent : ComponentBase { }
+
+    [Route("/not-found")]
+    public class TestNotFoundPageComponent : ComponentBase { }
 }

From 935a879a3d506e318631560c060abcbc4843dd1c Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 9 Jul 2025 07:53:09 +0000
Subject: [PATCH 03/10] Remove all tests as requested - keep only validation
 logic

Co-authored-by: ilonatommy <32700855+ilonatommy@users.noreply.github.com>
---
 .../Components/test/Routing/RouterTest.cs     | 70 -------------------
 1 file changed, 70 deletions(-)

diff --git a/src/Components/Components/test/Routing/RouterTest.cs b/src/Components/Components/test/Routing/RouterTest.cs
index 76aece62db60..f393a2edccf0 100644
--- a/src/Components/Components/test/Routing/RouterTest.cs
+++ b/src/Components/Components/test/Routing/RouterTest.cs
@@ -265,73 +265,6 @@ await _renderer.Dispatcher.InvokeAsync(() =>
         Assert.Equal("Not found", renderedFrame.TextContent);
     }
 
-    [Fact]
-    public async Task ThrowsIfBothNotFoundAndNotFoundPageAreSet()
-    {
-        // Arrange
-        var parameters = new Dictionary<string, object>
-        {
-            { nameof(Router.AppAssembly), typeof(RouterTest).Assembly },
-            { nameof(Router.NotFound), (RenderFragment)(builder => builder.AddContent(0, "Custom content")) },
-            { nameof(Router.NotFoundPage), typeof(TestNotFoundPageComponent) },
-        };
-
-        // Act & Assert
-        var exception = await Assert.ThrowsAsync<InvalidOperationException>(async () =>
-            await _renderer.Dispatcher.InvokeAsync(() =>
-                _router.SetParametersAsync(ParameterView.FromDictionary(parameters))));
-
-        Assert.Contains("cannot have both NotFound and NotFoundPage parameters set", exception.Message);
-    }
-
-    [Fact]
-    public async Task UsesNotFoundPageIfSpecified()
-    {
-        // Arrange
-        _navigationManager.NotifyLocationChanged("https://www.example.com/subdir/nonexistent", false);
-        var parameters = new Dictionary<string, object>
-        {
-            { nameof(Router.AppAssembly), typeof(RouterTest).Assembly },
-            { nameof(Router.NotFoundPage), typeof(TestNotFoundPageComponent) },
-        };
-
-        // Act
-        await _renderer.Dispatcher.InvokeAsync(() =>
-            _router.SetParametersAsync(ParameterView.FromDictionary(parameters)));
-
-        // Assert
-        var batch = _renderer.Batches.First();
-        var renderedFrame = batch.ReferenceFrames.Skip(1).First(); // Skip the RouteView frame
-        Assert.Equal(RenderTreeFrameType.Attribute, renderedFrame.FrameType);
-        Assert.Equal(nameof(RouteView.RouteData), renderedFrame.AttributeName);
-        var routeData = (RouteData)renderedFrame.AttributeValue;
-        Assert.Equal(typeof(TestNotFoundPageComponent), routeData.PageType);
-    }
-
-    [Fact]
-    public async Task UsesNotFoundPageOverNotFound()
-    {
-        // Arrange - This test verifies that if only NotFoundPage is set (not both), it takes precedence over default
-        _navigationManager.NotifyLocationChanged("https://www.example.com/subdir/nonexistent", false);
-        var parameters = new Dictionary<string, object>
-        {
-            { nameof(Router.AppAssembly), typeof(RouterTest).Assembly },
-            { nameof(Router.NotFoundPage), typeof(TestNotFoundPageComponent) },
-        };
-
-        // Act
-        await _renderer.Dispatcher.InvokeAsync(() =>
-            _router.SetParametersAsync(ParameterView.FromDictionary(parameters)));
-
-        // Assert
-        var batch = _renderer.Batches.First();
-        var renderedFrame = batch.ReferenceFrames.Skip(1).First(); // Skip the RouteView frame
-        Assert.Equal(RenderTreeFrameType.Attribute, renderedFrame.FrameType);
-        Assert.Equal(nameof(RouteView.RouteData), renderedFrame.AttributeName);
-        var routeData = (RouteData)renderedFrame.AttributeValue;
-        Assert.Equal(typeof(TestNotFoundPageComponent), routeData.PageType);
-    }
-
     internal class TestNavigationManager : NavigationManager
     {
         public TestNavigationManager() =>
@@ -373,7 +306,4 @@ public class MatchAnythingComponent : ComponentBase { }
 
     [Route("a/b/c")]
     public class MultiSegmentRouteComponent : ComponentBase { }
-
-    [Route("/not-found")]
-    public class TestNotFoundPageComponent : ComponentBase { }
 }

From 4bef8cc28e9b210c7c8a23a2186a8f048e679a2f Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 9 Jul 2025 08:26:16 +0000
Subject: [PATCH 04/10] Replace exception with warning logging for
 NotFound/NotFoundPage validation

Co-authored-by: ilonatommy <32700855+ilonatommy@users.noreply.github.com>
---
 .../Components/src/Routing/Router.cs          | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/Components/Components/src/Routing/Router.cs b/src/Components/Components/src/Routing/Router.cs
index 79a48ec9f973..7a5599fcefb3 100644
--- a/src/Components/Components/src/Routing/Router.cs
+++ b/src/Components/Components/src/Routing/Router.cs
@@ -70,6 +70,7 @@ static readonly IReadOnlyDictionary<string, object> _emptyParametersDictionary
     /// Gets or sets the content to display when no match is found for the requested route.
     /// </summary>
     [Parameter]
+    [Obsolete("NotFound is deprecated. Use NotFoundPage instead.")]
     public RenderFragment NotFound { get; set; }
 
     /// <summary>
@@ -141,13 +142,14 @@ public async Task SetParametersAsync(ParameterView parameters)
             throw new InvalidOperationException($"The {nameof(Router)} component requires a value for the parameter {nameof(Found)}.");
         }
 
-        if (NotFound != null && NotFoundPage != null)
-        {
-            throw new InvalidOperationException($"The {nameof(Router)} component cannot have both {nameof(NotFound)} and {nameof(NotFoundPage)} parameters set. Use either {nameof(NotFound)} render fragment or {nameof(NotFoundPage)} component type, but not both.");
-        }
-
         if (NotFoundPage != null)
         {
+#pragma warning disable CS0618 // Type or member is obsolete
+            if (NotFound != null)
+            {
+                Log.BothNotFoundParametersSet(_logger);
+            }
+#pragma warning restore CS0618 // Type or member is obsolete
             if (!typeof(IComponent).IsAssignableFrom(NotFoundPage))
             {
                 throw new InvalidOperationException($"The type {NotFoundPage.FullName} " +
@@ -406,10 +408,12 @@ private void RenderNotFound()
                     new RouteData(NotFoundPage, _emptyParametersDictionary));
                 builder.CloseComponent();
             }
+#pragma warning disable CS0618 // Type or member is obsolete
             else if (NotFound != null)
             {
                 NotFound(builder);
             }
+#pragma warning restore CS0618 // Type or member is obsolete
             else
             {
                 DefaultNotFoundContent(builder);
@@ -434,6 +438,7 @@ async Task IHandleAfterRender.OnAfterRenderAsync()
 
     private static partial class Log
     {
+#pragma warning disable CS0618 // Type or member is obsolete
         [LoggerMessage(1, LogLevel.Debug, $"Displaying {nameof(NotFound)} because path '{{Path}}' with base URI '{{BaseUri}}' does not match any component route", EventName = "DisplayingNotFound")]
         internal static partial void DisplayingNotFound(ILogger logger, string path, string baseUri);
 
@@ -445,5 +450,9 @@ private static partial class Log
 
         [LoggerMessage(4, LogLevel.Debug, $"Displaying {nameof(NotFound)} on request", EventName = "DisplayingNotFoundOnRequest")]
         internal static partial void DisplayingNotFound(ILogger logger);
+#pragma warning restore CS0618 // Type or member is obsolete
+
+        [LoggerMessage(5, LogLevel.Warning, "Both NotFound and NotFoundPage parameters are set on Router component. NotFoundPage is preferred and NotFound will be deprecated. Consider using only NotFoundPage.", EventName = "BothNotFoundParametersSet")]
+        internal static partial void BothNotFoundParametersSet(ILogger logger);
     }
 }

From c5e0c46f56144e98accbc88c492fd664ffa891b6 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 9 Jul 2025 10:34:05 +0000
Subject: [PATCH 05/10] Disable CS0618 obsolete warnings for RouterTest.cs

Co-authored-by: ilonatommy <32700855+ilonatommy@users.noreply.github.com>
---
 src/Components/Components/test/Routing/RouterTest.cs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/Components/Components/test/Routing/RouterTest.cs b/src/Components/Components/test/Routing/RouterTest.cs
index f393a2edccf0..4514a96d5bcb 100644
--- a/src/Components/Components/test/Routing/RouterTest.cs
+++ b/src/Components/Components/test/Routing/RouterTest.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#pragma warning disable CS0618 // Type or member is obsolete
+
 using System.Reflection;
 using Microsoft.AspNetCore.Components.RenderTree;
 using Microsoft.AspNetCore.Components.Test.Helpers;

From aa545628048cbcee638e03b0a1f31da766d76c8e Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 9 Jul 2025 12:30:02 +0000
Subject: [PATCH 06/10] Add unit test for warning when both NotFound and
 NotFoundPage are set

Co-authored-by: ilonatommy <32700855+ilonatommy@users.noreply.github.com>
---
 .../Components/test/Routing/RouterTest.cs     | 84 +++++++++++++++++++
 1 file changed, 84 insertions(+)

diff --git a/src/Components/Components/test/Routing/RouterTest.cs b/src/Components/Components/test/Routing/RouterTest.cs
index 4514a96d5bcb..3c860656db49 100644
--- a/src/Components/Components/test/Routing/RouterTest.cs
+++ b/src/Components/Components/test/Routing/RouterTest.cs
@@ -267,6 +267,43 @@ await _renderer.Dispatcher.InvokeAsync(() =>
         Assert.Equal("Not found", renderedFrame.TextContent);
     }
 
+    [Fact]
+    public async Task LogsWarningWhenBothNotFoundAndNotFoundPageAreSet()
+    {
+        // Arrange
+        var logger = new TestLogger<Router>();
+        var services = new ServiceCollection();
+        services.AddSingleton<ILoggerFactory>(new TestLoggerFactory(logger));
+        services.AddSingleton<NavigationManager>(_navigationManager);
+        services.AddSingleton<INavigationInterception, TestNavigationInterception>();
+        services.AddSingleton<IScrollToLocationHash, TestScrollToLocationHash>();
+        var serviceProvider = services.BuildServiceProvider();
+
+        var renderer = new TestRenderer(serviceProvider);
+        renderer.ShouldHandleExceptions = true;
+        var router = (Router)renderer.InstantiateComponent<Router>();
+        router.AppAssembly = Assembly.GetExecutingAssembly();
+        router.Found = routeData => (builder) => builder.AddContent(0, $"Rendering route matching {routeData.PageType}");
+        renderer.AssignRootComponentId(router);
+
+        var parameters = new Dictionary<string, object>
+        {
+            { nameof(Router.AppAssembly), typeof(RouterTest).Assembly },
+            { nameof(Router.NotFound), (RenderFragment)(builder => builder.AddContent(0, "Custom not found")) },
+            { nameof(Router.NotFoundPage), typeof(NotFoundTestComponent) }
+        };
+
+        // Act
+        await renderer.Dispatcher.InvokeAsync(() =>
+            router.SetParametersAsync(ParameterView.FromDictionary(parameters)));
+
+        // Assert
+        var warningLogs = logger.LogEntries.Where(entry => entry.LogLevel == LogLevel.Warning).ToList();
+        Assert.Single(warningLogs);
+        Assert.Contains("Both NotFound and NotFoundPage parameters are set on Router component", warningLogs[0].Message);
+        Assert.Contains("NotFoundPage is preferred and NotFound will be deprecated", warningLogs[0].Message);
+    }
+
     internal class TestNavigationManager : NavigationManager
     {
         public TestNavigationManager() =>
@@ -308,4 +345,51 @@ public class MatchAnythingComponent : ComponentBase { }
 
     [Route("a/b/c")]
     public class MultiSegmentRouteComponent : ComponentBase { }
+
+    [Route("not-found")]
+    public class NotFoundTestComponent : ComponentBase { }
+
+    public class TestLogger<T> : ILogger<T>
+    {
+        public List<LogEntry> LogEntries { get; } = new List<LogEntry>();
+
+        public IDisposable BeginScope<TState>(TState state) => null;
+
+        public bool IsEnabled(LogLevel logLevel) => true;
+
+        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
+        {
+            LogEntries.Add(new LogEntry
+            {
+                LogLevel = logLevel,
+                EventId = eventId,
+                Message = formatter(state, exception),
+                Exception = exception
+            });
+        }
+    }
+
+    public class LogEntry
+    {
+        public LogLevel LogLevel { get; set; }
+        public EventId EventId { get; set; }
+        public string Message { get; set; }
+        public Exception Exception { get; set; }
+    }
+
+    public class TestLoggerFactory : ILoggerFactory
+    {
+        private readonly ILogger _logger;
+
+        public TestLoggerFactory(ILogger logger)
+        {
+            _logger = logger;
+        }
+
+        public void AddProvider(ILoggerProvider provider) { }
+
+        public ILogger CreateLogger(string categoryName) => _logger;
+
+        public void Dispose() { }
+    }
 }

From c10c0d4cfc4e7a8c9e5fbe5482bbb000e79b6694 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 15 Jul 2025 08:06:28 +0000
Subject: [PATCH 07/10] Change warning to throwing exception for
 NotFound/NotFoundPage validation

Co-authored-by: ilonatommy <32700855+ilonatommy@users.noreply.github.com>
---
 .../Components/src/Routing/Router.cs          |  5 +----
 .../Components/test/Routing/RouterTest.cs     | 19 ++++++++-----------
 2 files changed, 9 insertions(+), 15 deletions(-)

diff --git a/src/Components/Components/src/Routing/Router.cs b/src/Components/Components/src/Routing/Router.cs
index 7a5599fcefb3..2bec7fdd24d3 100644
--- a/src/Components/Components/src/Routing/Router.cs
+++ b/src/Components/Components/src/Routing/Router.cs
@@ -147,7 +147,7 @@ public async Task SetParametersAsync(ParameterView parameters)
 #pragma warning disable CS0618 // Type or member is obsolete
             if (NotFound != null)
             {
-                Log.BothNotFoundParametersSet(_logger);
+                throw new InvalidOperationException("Both NotFound and NotFoundPage parameters are set on Router component. NotFoundPage is preferred and NotFound will be deprecated. Consider using only NotFoundPage.");
             }
 #pragma warning restore CS0618 // Type or member is obsolete
             if (!typeof(IComponent).IsAssignableFrom(NotFoundPage))
@@ -451,8 +451,5 @@ private static partial class Log
         [LoggerMessage(4, LogLevel.Debug, $"Displaying {nameof(NotFound)} on request", EventName = "DisplayingNotFoundOnRequest")]
         internal static partial void DisplayingNotFound(ILogger logger);
 #pragma warning restore CS0618 // Type or member is obsolete
-
-        [LoggerMessage(5, LogLevel.Warning, "Both NotFound and NotFoundPage parameters are set on Router component. NotFoundPage is preferred and NotFound will be deprecated. Consider using only NotFoundPage.", EventName = "BothNotFoundParametersSet")]
-        internal static partial void BothNotFoundParametersSet(ILogger logger);
     }
 }
diff --git a/src/Components/Components/test/Routing/RouterTest.cs b/src/Components/Components/test/Routing/RouterTest.cs
index 3c860656db49..96d7b9dea109 100644
--- a/src/Components/Components/test/Routing/RouterTest.cs
+++ b/src/Components/Components/test/Routing/RouterTest.cs
@@ -268,12 +268,11 @@ await _renderer.Dispatcher.InvokeAsync(() =>
     }
 
     [Fact]
-    public async Task LogsWarningWhenBothNotFoundAndNotFoundPageAreSet()
+    public async Task ThrowsExceptionWhenBothNotFoundAndNotFoundPageAreSet()
     {
         // Arrange
-        var logger = new TestLogger<Router>();
         var services = new ServiceCollection();
-        services.AddSingleton<ILoggerFactory>(new TestLoggerFactory(logger));
+        services.AddSingleton<ILoggerFactory>(NullLoggerFactory.Instance);
         services.AddSingleton<NavigationManager>(_navigationManager);
         services.AddSingleton<INavigationInterception, TestNavigationInterception>();
         services.AddSingleton<IScrollToLocationHash, TestScrollToLocationHash>();
@@ -293,15 +292,13 @@ public async Task LogsWarningWhenBothNotFoundAndNotFoundPageAreSet()
             { nameof(Router.NotFoundPage), typeof(NotFoundTestComponent) }
         };
 
-        // Act
-        await renderer.Dispatcher.InvokeAsync(() =>
-            router.SetParametersAsync(ParameterView.FromDictionary(parameters)));
+        // Act & Assert
+        var exception = await Assert.ThrowsAsync<InvalidOperationException>(async () =>
+            await renderer.Dispatcher.InvokeAsync(() =>
+                router.SetParametersAsync(ParameterView.FromDictionary(parameters))));
 
-        // Assert
-        var warningLogs = logger.LogEntries.Where(entry => entry.LogLevel == LogLevel.Warning).ToList();
-        Assert.Single(warningLogs);
-        Assert.Contains("Both NotFound and NotFoundPage parameters are set on Router component", warningLogs[0].Message);
-        Assert.Contains("NotFoundPage is preferred and NotFound will be deprecated", warningLogs[0].Message);
+        Assert.Contains("Both NotFound and NotFoundPage parameters are set on Router component", exception.Message);
+        Assert.Contains("NotFoundPage is preferred and NotFound will be deprecated", exception.Message);
     }
 
     internal class TestNavigationManager : NavigationManager

From 0712e4c3423d7c777493b5c50234e5eccdfc2280 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 15 Jul 2025 08:20:32 +0000
Subject: [PATCH 08/10] Fix test assets and clean up test code as requested

Co-authored-by: ilonatommy <32700855+ilonatommy@users.noreply.github.com>
---
 .../Components/test/Routing/RouterTest.cs     | 43 -------------------
 .../RazorComponents/App.razor                 | 26 ++++++++---
 .../Components.WasmMinimal/Routes.razor       | 26 ++++++++---
 3 files changed, 38 insertions(+), 57 deletions(-)

diff --git a/src/Components/Components/test/Routing/RouterTest.cs b/src/Components/Components/test/Routing/RouterTest.cs
index 96d7b9dea109..460444b919ca 100644
--- a/src/Components/Components/test/Routing/RouterTest.cs
+++ b/src/Components/Components/test/Routing/RouterTest.cs
@@ -346,47 +346,4 @@ public class MultiSegmentRouteComponent : ComponentBase { }
     [Route("not-found")]
     public class NotFoundTestComponent : ComponentBase { }
 
-    public class TestLogger<T> : ILogger<T>
-    {
-        public List<LogEntry> LogEntries { get; } = new List<LogEntry>();
-
-        public IDisposable BeginScope<TState>(TState state) => null;
-
-        public bool IsEnabled(LogLevel logLevel) => true;
-
-        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
-        {
-            LogEntries.Add(new LogEntry
-            {
-                LogLevel = logLevel,
-                EventId = eventId,
-                Message = formatter(state, exception),
-                Exception = exception
-            });
-        }
-    }
-
-    public class LogEntry
-    {
-        public LogLevel LogLevel { get; set; }
-        public EventId EventId { get; set; }
-        public string Message { get; set; }
-        public Exception Exception { get; set; }
-    }
-
-    public class TestLoggerFactory : ILoggerFactory
-    {
-        private readonly ILogger _logger;
-
-        public TestLoggerFactory(ILogger logger)
-        {
-            _logger = logger;
-        }
-
-        public void AddProvider(ILoggerProvider provider) { }
-
-        public ILogger CreateLogger(string categoryName) => _logger;
-
-        public void Dispose() { }
-    }
 }
diff --git a/src/Components/test/testassets/Components.TestServer/RazorComponents/App.razor b/src/Components/test/testassets/Components.TestServer/RazorComponents/App.razor
index 2219da3955d2..d2adde64c256 100644
--- a/src/Components/test/testassets/Components.TestServer/RazorComponents/App.razor
+++ b/src/Components/test/testassets/Components.TestServer/RazorComponents/App.razor
@@ -30,13 +30,25 @@
     <HeadOutlet />
 </head>
 <body>
-    <Router AppAssembly="@typeof(App).Assembly" AdditionalAssemblies="new[] { typeof(TestContentPackage.NotFound.NotFoundPage).Assembly }" NotFoundPage="NotFoundPageType">
-        <Found Context="routeData">
-            <RouteView RouteData="@routeData" />
-            <FocusOnNavigate RouteData="@routeData" Selector="[data-focus-on-navigate]" />
-        </Found>
-        <NotFound><p id="not-found-fragment">There's nothing here</p></NotFound>
-    </Router>
+    @if (NotFoundPageType != null)
+    {
+        <Router AppAssembly="@typeof(App).Assembly" AdditionalAssemblies="new[] { typeof(TestContentPackage.NotFound.NotFoundPage).Assembly }" NotFoundPage="NotFoundPageType">
+            <Found Context="routeData">
+                <RouteView RouteData="@routeData" />
+                <FocusOnNavigate RouteData="@routeData" Selector="[data-focus-on-navigate]" />
+            </Found>
+        </Router>
+    }
+    else
+    {
+        <Router AppAssembly="@typeof(App).Assembly" AdditionalAssemblies="new[] { typeof(TestContentPackage.NotFound.NotFoundPage).Assembly }">
+            <Found Context="routeData">
+                <RouteView RouteData="@routeData" />
+                <FocusOnNavigate RouteData="@routeData" Selector="[data-focus-on-navigate]" />
+            </Found>
+            <NotFound><p id="not-found-fragment">There's nothing here</p></NotFound>
+        </Router>
+    }
     <script>
         // This script must come before blazor.web.js to test that
         // the framework does the right thing when an element is already focused.
diff --git a/src/Components/test/testassets/Components.WasmMinimal/Routes.razor b/src/Components/test/testassets/Components.WasmMinimal/Routes.razor
index 010176d437e7..e8bfa4af46b2 100644
--- a/src/Components/test/testassets/Components.WasmMinimal/Routes.razor
+++ b/src/Components/test/testassets/Components.WasmMinimal/Routes.razor
@@ -23,10 +23,22 @@
     }
 }
 
-<Router AppAssembly="@typeof(Program).Assembly" AdditionalAssemblies="new[] { typeof(TestContentPackage.NotFound.NotFoundPage).Assembly }" NotFoundPage="NotFoundPageType">
-    <Found Context="routeData">
-        <RouteView RouteData="@routeData" />
-        <FocusOnNavigate RouteData="@routeData" Selector="h1" />
-    </Found>
-    <NotFound><p id="not-found-fragment">There's nothing here</p></NotFound>
-</Router>
+@if (NotFoundPageType != null)
+{
+    <Router AppAssembly="@typeof(Program).Assembly" AdditionalAssemblies="new[] { typeof(TestContentPackage.NotFound.NotFoundPage).Assembly }" NotFoundPage="NotFoundPageType">
+        <Found Context="routeData">
+            <RouteView RouteData="@routeData" />
+            <FocusOnNavigate RouteData="@routeData" Selector="h1" />
+        </Found>
+    </Router>
+}
+else
+{
+    <Router AppAssembly="@typeof(Program).Assembly" AdditionalAssemblies="new[] { typeof(TestContentPackage.NotFound.NotFoundPage).Assembly }">
+        <Found Context="routeData">
+            <RouteView RouteData="@routeData" />
+            <FocusOnNavigate RouteData="@routeData" Selector="h1" />
+        </Found>
+        <NotFound><p id="not-found-fragment">There's nothing here</p></NotFound>
+    </Router>
+}

From b7e96d13bb766633a53b60fa311452b9f45e0702 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 15 Jul 2025 09:55:38 +0000
Subject: [PATCH 09/10] Simplify error message and use nameof for property
 names

Co-authored-by: javiercn <6995051+javiercn@users.noreply.github.com>
---
 src/Components/Components/src/Routing/Router.cs      | 2 +-
 src/Components/Components/test/Routing/RouterTest.cs | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/Components/Components/src/Routing/Router.cs b/src/Components/Components/src/Routing/Router.cs
index 2bec7fdd24d3..673950373e28 100644
--- a/src/Components/Components/src/Routing/Router.cs
+++ b/src/Components/Components/src/Routing/Router.cs
@@ -147,7 +147,7 @@ public async Task SetParametersAsync(ParameterView parameters)
 #pragma warning disable CS0618 // Type or member is obsolete
             if (NotFound != null)
             {
-                throw new InvalidOperationException("Both NotFound and NotFoundPage parameters are set on Router component. NotFoundPage is preferred and NotFound will be deprecated. Consider using only NotFoundPage.");
+                throw new InvalidOperationException($"Setting {nameof(NotFound)} and {nameof(NotFoundPage)} properties simultaneously is not supported. Use either {nameof(NotFound)} or {nameof(NotFoundPage)}.");
             }
 #pragma warning restore CS0618 // Type or member is obsolete
             if (!typeof(IComponent).IsAssignableFrom(NotFoundPage))
diff --git a/src/Components/Components/test/Routing/RouterTest.cs b/src/Components/Components/test/Routing/RouterTest.cs
index 460444b919ca..46bbb04a030f 100644
--- a/src/Components/Components/test/Routing/RouterTest.cs
+++ b/src/Components/Components/test/Routing/RouterTest.cs
@@ -297,8 +297,8 @@ public async Task ThrowsExceptionWhenBothNotFoundAndNotFoundPageAreSet()
             await renderer.Dispatcher.InvokeAsync(() =>
                 router.SetParametersAsync(ParameterView.FromDictionary(parameters))));
 
-        Assert.Contains("Both NotFound and NotFoundPage parameters are set on Router component", exception.Message);
-        Assert.Contains("NotFoundPage is preferred and NotFound will be deprecated", exception.Message);
+        Assert.Contains("Setting NotFound and NotFoundPage properties simultaneously is not supported", exception.Message);
+        Assert.Contains("Use either NotFound or NotFoundPage", exception.Message);
     }
 
     internal class TestNavigationManager : NavigationManager

From 337dbe4469ad75d59895cb6419c3233c838a990b Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <itomkowicz@microsoft.com>
Date: Wed, 16 Jul 2025 16:53:04 +0200
Subject: [PATCH 10/10] Remove NotFound fragment from templates - we have
 NotFoundPage instead.

---
 .../content/ComponentsWebAssembly-CSharp/App.razor   | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/src/ProjectTemplates/Web.ProjectTemplates/content/ComponentsWebAssembly-CSharp/App.razor b/src/ProjectTemplates/Web.ProjectTemplates/content/ComponentsWebAssembly-CSharp/App.razor
index 1962afdd3be6..c177d88dce9e 100644
--- a/src/ProjectTemplates/Web.ProjectTemplates/content/ComponentsWebAssembly-CSharp/App.razor
+++ b/src/ProjectTemplates/Web.ProjectTemplates/content/ComponentsWebAssembly-CSharp/App.razor
@@ -4,12 +4,6 @@
         <RouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)"/>
         <FocusOnNavigate RouteData="@routeData" Selector="h1" />
     </Found>
-    <NotFound>
-        <PageTitle>Not found</PageTitle>
-        <LayoutView Layout="@typeof(MainLayout)">
-            <p role="alert">Sorry, there's nothing at this address.</p>
-        </LayoutView>
-    </NotFound>
 </Router>
 #else
 <CascadingAuthenticationState>
@@ -29,12 +23,6 @@
             </AuthorizeRouteView>
             <FocusOnNavigate RouteData="@routeData" Selector="h1" />
         </Found>
-        <NotFound>
-            <PageTitle>Not found</PageTitle>
-            <LayoutView Layout="@typeof(MainLayout)">
-                <p role="alert">Sorry, there's nothing at this address.</p>
-            </LayoutView>
-        </NotFound>
     </Router>
 </CascadingAuthenticationState>
 #endif*@

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