Improve Components error handling

src/Components/Blazor/Blazor/src/Hosting/WebAssemblyBlazorApplicationBuilder.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Threading.Tasks;
 using Microsoft.AspNetCore.Blazor.Rendering;
 using Microsoft.AspNetCore.Components.Builder;
 
@@ -35,13 +36,13 @@ public void AddComponent(Type componentType, string domElementSelector)
             Entries.Add((componentType, domElementSelector));
         }
 
-        public WebAssemblyRenderer CreateRenderer()
+        public async Task<WebAssemblyRenderer> CreateRendererAsync()
         {
             var renderer = new WebAssemblyRenderer(Services);
             for (var i = 0; i < Entries.Count; i++)
             {
-                var entry = Entries[i];
-                renderer.AddComponent(entry.componentType, entry.domElementSelector);
+                var (componentType, domElementSelector) = Entries[i];
+                await renderer.AddComponentAsync(componentType, domElementSelector);
             }
 
             return renderer;

src/Components/Blazor/Blazor/src/Hosting/WebAssemblyHost.cs

@@ -42,6 +42,11 @@ public Task StartAsync(CancellationToken cancellationToken = default)
             JSRuntime.SetCurrentJSRuntime(_runtime);
             SetBrowserHttpMessageHandlerAsDefault();
 
+            return StartAsyncAwaited();
+        }
+
+        private async Task StartAsyncAwaited()
+        {
             var scopeFactory = Services.GetRequiredService<IServiceScopeFactory>();
             _scope = scopeFactory.CreateScope();
 
@@ -61,7 +66,7 @@ public Task StartAsync(CancellationToken cancellationToken = default)
                 var builder = new WebAssemblyBlazorApplicationBuilder(_scope.ServiceProvider);
                 startup.Configure(builder, _scope.ServiceProvider);
 
-                _renderer = builder.CreateRenderer();
+                _renderer = await builder.CreateRendererAsync();
             }
             catch
             {
@@ -76,9 +81,6 @@ public Task StartAsync(CancellationToken cancellationToken = default)
 
                 throw;
             }
-
-
-            return Task.CompletedTask;
         }
 
         public Task StopAsync(CancellationToken cancellationToken = default)

src/Components/Blazor/Blazor/src/Rendering/WebAssemblyRenderer.cs

@@ -1,14 +1,13 @@
 // 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 System.Threading.Tasks;
 using Microsoft.AspNetCore.Components;
 using Microsoft.AspNetCore.Components.Browser;
 using Microsoft.AspNetCore.Components.Rendering;
 using Microsoft.JSInterop;
 using Mono.WebAssembly.Interop;
-using System;
-using System.Threading;
-using System.Threading.Tasks;
 
 namespace Microsoft.AspNetCore.Blazor.Rendering
 {
@@ -24,7 +23,7 @@ public class WebAssemblyRenderer : Renderer
         /// Constructs an instance of <see cref="WebAssemblyRenderer"/>.
         /// </summary>
         /// <param name="serviceProvider">The <see cref="IServiceProvider"/> to use when initializing components.</param>
-        public WebAssemblyRenderer(IServiceProvider serviceProvider): base(serviceProvider)
+        public WebAssemblyRenderer(IServiceProvider serviceProvider) : base(serviceProvider)
         {
             // The browser renderer registers and unregisters itself with the static
             // registry. This works well with the WebAssembly runtime, and is simple for the
@@ -38,19 +37,26 @@ public WebAssemblyRenderer(IServiceProvider serviceProvider): base(serviceProvid
         /// </summary>
         /// <typeparam name="TComponent">The type of the component.</typeparam>
         /// <param name="domElementSelector">A CSS selector that uniquely identifies a DOM element.</param>
-        public void AddComponent<TComponent>(string domElementSelector)
-            where TComponent: IComponent
-        {
-            AddComponent(typeof(TComponent), domElementSelector);
-        }
+        /// <returns>A <see cref="Task"/> that represents the asynchronous rendering of the added component.</returns>
+        /// <remarks>
+        /// Callers of this method may choose to ignore the returned <see cref="Task"/> if they do not
+        /// want to await the rendering of the added component.
+        /// </remarks>
+        public Task AddComponentAsync<TComponent>(string domElementSelector) where TComponent : IComponent
+            => AddComponentAsync(typeof(TComponent), domElementSelector);
 
         /// <summary>
         /// Associates the <see cref="IComponent"/> with the <see cref="WebAssemblyRenderer"/>,
         /// causing it to be displayed in the specified DOM element.
         /// </summary>
         /// <param name="componentType">The type of the component.</param>
         /// <param name="domElementSelector">A CSS selector that uniquely identifies a DOM element.</param>
-        public void AddComponent(Type componentType, string domElementSelector)
+        /// <returns>A <see cref="Task"/> that represents the asynchronous rendering of the added component.</returns>
+        /// <remarks>
+        /// Callers of this method may choose to ignore the returned <see cref="Task"/> if they do not
+        /// want to await the rendering of the added component.
+        /// </remarks>
+        public Task AddComponentAsync(Type componentType, string domElementSelector)
         {
             var component = InstantiateComponent(componentType);
             var componentId = AssignRootComponentId(component);
@@ -66,7 +72,7 @@ public void AddComponent(Type componentType, string domElementSelector)
                 domElementSelector,
                 componentId);
 
-            RenderRootComponent(componentId);
+            return RenderRootComponentAsync(componentId);
         }
 
         /// <inheritdoc />
@@ -93,5 +99,22 @@ protected override Task UpdateDisplayAsync(in RenderBatch batch)
                 throw new NotImplementedException($"{nameof(WebAssemblyRenderer)} is supported only with in-process JS runtimes.");
             }
         }
+
+        /// <inheritdoc />
+        protected override void HandleException(Exception exception)
+        {
+            Console.Error.WriteLine($"Unhandled exception rendering component:");
+            if (exception is AggregateException aggregateException)
+            {
+                foreach (var innerException in aggregateException.Flatten().InnerExceptions)
+                {
+                    Console.Error.WriteLine(innerException);
+                }
+            }
+            else
+            {
+                Console.Error.WriteLine(exception);
+            }
+        }
     }
 }

src/Components/Blazor/Build/test/RazorIntegrationTestBase.cs

@@ -443,6 +443,11 @@ public TestRenderer() : base(new TestServiceProvider(), CreateDefaultDispatcher(
             public void AttachComponent(IComponent component)
                 => AssignRootComponentId(component);
 
+            protected override void HandleException(Exception exception)
+            {
+                throw new NotImplementedException();
+            }
+
             protected override Task UpdateDisplayAsync(in RenderBatch renderBatch)
             {
                 LatestBatchReferenceFrames = renderBatch.ReferenceFrames.ToArray();

src/Components/Browser/src/RendererRegistryEventDispatcher.cs

@@ -1,9 +1,10 @@
 // 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 System.Threading.Tasks;
 using Microsoft.AspNetCore.Components.Rendering;
 using Microsoft.JSInterop;
-using System;
 
 namespace Microsoft.AspNetCore.Components.Browser
 {
@@ -16,12 +17,13 @@ public static class RendererRegistryEventDispatcher
         /// For framework use only.
         /// </summary>
         [JSInvokable(nameof(DispatchEvent))]
-        public static void DispatchEvent(
+        public static Task DispatchEvent(
             BrowserEventDescriptor eventDescriptor, string eventArgsJson)
         {
             var eventArgs = ParseEventArgsJson(eventDescriptor.EventArgsType, eventArgsJson);
             var renderer = RendererRegistry.Current.Find(eventDescriptor.BrowserRendererId);
-            renderer.DispatchEvent(
+
+            return renderer.DispatchEventAsync(
                 eventDescriptor.ComponentId,
                 eventDescriptor.EventHandlerId,
                 eventArgs);

src/Components/Components/perf/RenderTreeDiffBuilderBenchmark.cs

@@ -91,6 +91,11 @@ public FakeRenderer()
             {
             }
 
+            protected override void HandleException(Exception exception)
+            {
+                throw new NotImplementedException();
+            }
+
             protected override Task UpdateDisplayAsync(in RenderBatch renderBatch)
                 => Task.CompletedTask;
         }