Let error boundaries catch their own inline errors

Author: SteveSandersonMS

src/Components/Components/src/RenderTree/Renderer.cs

@@ -404,10 +404,7 @@ private bool TrySendExceptionToErrorBoundary(IComponent? errorSource, Exception
             // If it becomes problematic, we can maintain a lookup from component instance to ID.
             var componentState = _componentStateById.FirstOrDefault(kvp => kvp.Value.Component == errorSource).Value;
 
-            // Find the closest IErrorBoundary, if any. Start looking at the first parent, to ensure
-            // that an error boundary component doesn't try to handle its own errors, as that could
-            // be an infinite loop.
-            componentState = componentState?.ParentComponentState;
+            // Find the closest IErrorBoundary, if any
             while (componentState is not null)
             {
                 if (componentState.Component is IErrorBoundary errorBoundary)

src/Components/Samples/BlazorServerApp/Pages/ErrorMaker.razor

@@ -45,6 +45,22 @@
             <ErrorCausingCounter />
         </ErrorIgnorer>
     </fieldset>
+
+    <fieldset>
+        <legend>Exception inline in error boundary markup</legend>
+        <ErrorBoundary>
+            <ChildContent>
+                @if (throwInline) { throw new InvalidTimeZoneException("Inline exception"); }
+                 <p>Hello!</p>
+            </ChildContent>
+            <ErrorContent>
+                @if (throwInErrorContent) { throw new InvalidTimeZoneException("Inline exception in error content"); }
+                <p>There was an error: @context</p>
+            </ErrorContent>
+        </ErrorBoundary>
+        <button @onclick="@(() => throwInline = true)">Throw in child content</button>
+        <button @onclick="@(() => throwInErrorContent = true)">Throw in error content</button>
+    </fieldset>
 </fieldset>
 
 @code {
@@ -98,6 +114,8 @@
     private bool throwInOnAfterRender;
     private bool throwInOnAfterRenderAsync;
     private bool throwWhileRendering;
+    private bool throwInline;
+    private bool throwInErrorContent;
 
     void EventHandlerErrorSync()
         => throw new InvalidTimeZoneException("Synchronous error from event handler");

src/Components/Web/src/Web/ErrorBoundary.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Runtime.ExceptionServices;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Components.Rendering;
 
@@ -26,6 +27,13 @@ public sealed class ErrorBoundary : ComponentBase, IErrorBoundary
 
         public void HandleException(Exception exception)
         {
+            if (_currentException is not null)
+            {
+                // If there's an error while we're already displaying error content, then it's the
+                // error content that's failing. Avoid the risk of an infinite error rendering loop.
+                ExceptionDispatchInfo.Capture(exception).Throw();
+            }
+
             _ = ErrorBoundaryLogger!.LogErrorAsync(exception, clientOnly: false);
 
             _currentException = exception;