Fix ErrorBoundary not rendering ErrorContent when multiple exceptions occur

src/Components/Components/src/ErrorBoundaryBase.cs

@@ -33,6 +33,11 @@ public abstract class ErrorBoundaryBase : ComponentBase, IErrorBoundary
     /// </summary>
     protected Exception? CurrentException { get; private set; }
 
+    /// <summary>
+    /// Gets a value indicating whether the error boundary is currently in an error state.
+    /// </summary>
+    internal bool IsInErrorState => CurrentException is not null;
+
     /// <summary>
     /// Resets the error boundary to a non-errored state. If the error boundary is not
     /// already in an errored state, the call has no effect.

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

@@ -1169,7 +1169,12 @@ private void HandleExceptionViaErrorBoundary(Exception error, ComponentState? er
                 // Don't just trust the error boundary to dispose its subtree - force it to do so by
                 // making it render an empty fragment. Ensures that failed components don't continue to
                 // operate, which would be a whole new kind of edge case to support forever.
-                AddToRenderQueue(candidate.ComponentId, builder => { });
+                // However, if the error boundary already has an error (is in error state),
+                // don't queue an empty render as it would override the error content that should be displayed.
+                if (errorBoundary is ErrorBoundaryBase errorBoundaryBase && !errorBoundaryBase.IsInErrorState)
+                {
+                    AddToRenderQueue(candidate.ComponentId, builder => { });
+                }
 
                 try
                 {

src/Components/test/E2ETest/Tests/ErrorBoundaryTest.cs

@@ -158,6 +158,20 @@ public void CanHandleMultipleAsyncErrorsFromDescendants()
         AssertGlobalErrorState(false);
     }
 
+    [Fact]
+    public void CanHandleTwoErrorsInSameComponent()
+    {
+        var container = Browser.Exists(By.Id("two-errors-test"));
+
+        // Trigger the component with two errors
+        container.FindElement(By.Id("show-two-errors-component")).Click();
+
+        // Should show error content, not be blank
+        Browser.Exists(By.ClassName("two-errors-error-content"));
+
+        AssertGlobalErrorState(false);
+    }
+
     void AssertGlobalErrorState(bool hasGlobalError)
     {
         var globalErrorUi = Browser.Exists(By.Id("blazor-error-ui"));

src/Components/test/testassets/BasicTestApp/ErrorBoundaryTest/ComponentWithTwoErrors.razor

@@ -0,0 +1,12 @@
+@{
+    throw new Exception("error2");
+}
+
+@code
+{
+    protected override async Task OnInitializedAsync()
+    {
+        await Task.Yield(); // Make it actually async
+        throw new Exception("error");
+    }
+}

src/Components/test/testassets/BasicTestApp/ErrorBoundaryTest/ErrorBoundaryCases.razor

@@ -99,6 +99,24 @@
     <button class="throw-in-children" @onclick="@(() => { multipleChildrenBeginDelayedError = true; })">Cause multiple errors</button>
 </div>
 
+<hr />
+<h2>Two different errors in same component</h2>
+<p>This tests the case where a component throws in both OnInitializedAsync and during rendering.</p>
+<div id="two-errors-test">
+    @if (showTwoErrorsComponent)
+    {
+        <ErrorBoundary>
+            <ChildContent>
+                <ComponentWithTwoErrors />
+            </ChildContent>
+            <ErrorContent>
+                <div class="two-errors-error-content" style="background: red">@context</div>
+            </ErrorContent>
+        </ErrorBoundary>
+    }
+    <button id="show-two-errors-component" @onclick="@(() => showTwoErrorsComponent = true)">Show component with two errors</button>
+</div>
+
 <hr />
 <h2>Dispatch exception to renderer</h2>
 <p>Use DispatchExceptionAsync to see if exceptions are correctly dispatched to the renderer.</p>
@@ -122,6 +140,7 @@
     private bool disposalTestRemoveErrorBoundary;
     private bool disposalTestBeginDelayedError;
     private bool multipleChildrenBeginDelayedError;
+    private bool showTwoErrorsComponent;
 
     void EventHandlerErrorSync()
         => throw new InvalidTimeZoneException("Synchronous error from event handler");