Add validation to Router component to prevent both NotFound and NotFoundPage being set

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!>!

src/Components/Components/src/Routing/Router.cs

@@ -70,14 +70,15 @@ 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>
     /// Gets or sets the page content to display when no match is found for the requested route.
     /// </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.
@@ -143,6 +144,12 @@ public async Task SetParametersAsync(ParameterView parameters)
 
         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+#pragma warning disable CS0618 // Type or member is obsolete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+#pragma warning restore CS0618 // Type or member is obsolete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} " +
@@ -401,10 +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);
@@ -429,6 +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);
 
@@ -440,5 +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);
     }
 }