[release/9.0] Prevent unnecessary debugger stops for user-unhandled exceptions in Blazor apps with Just My Code enabled (#58573)

* Add [DebuggerDisableUserUnhandledExceptions] closer to user code

* Remove [DebuggerDisableUserUnhandledExceptions] from developer exception page middleware

Author: halter73

src/Components/Components/src/ComponentBase.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
 using Microsoft.AspNetCore.Components.Rendering;
 
 namespace Microsoft.AspNetCore.Components;
@@ -271,10 +272,22 @@ public virtual Task SetParametersAsync(ParameterView parameters)
         }
     }
 
+    // We do not want the debugger to consider NavigationExceptions caught by this method as user-unhandled.
+    [DebuggerDisableUserUnhandledExceptions]
     private async Task RunInitAndSetParametersAsync()
     {
-        OnInitialized();
-        var task = OnInitializedAsync();
+        Task task;
+
+        try
+        {
+            OnInitialized();
+            task = OnInitializedAsync();
+        }
+        catch (Exception ex) when (ex is not NavigationException)
+        {
+            Debugger.BreakForUserUnhandledException(ex);
+            throw;
+        }
 
         if (task.Status != TaskStatus.RanToCompletion && task.Status != TaskStatus.Canceled)
         {
@@ -307,10 +320,23 @@ private async Task RunInitAndSetParametersAsync()
         await CallOnParametersSetAsync();
     }
 
+    // We do not want the debugger to consider NavigationExceptions caught by this method as user-unhandled.
+    [DebuggerDisableUserUnhandledExceptions]
     private Task CallOnParametersSetAsync()
     {
-        OnParametersSet();
-        var task = OnParametersSetAsync();
+        Task task;
+
+        try
+        {
+            OnParametersSet();
+            task = OnParametersSetAsync();
+        }
+        catch (Exception ex) when (ex is not NavigationException)
+        {
+            Debugger.BreakForUserUnhandledException(ex);
+            throw;
+        }
+
         // If no async work is to be performed, i.e. the task has already ran to completion
         // or was canceled by the time we got to inspect it, avoid going async and re-invoking
         // StateHasChanged at the culmination of the async work.
@@ -326,6 +352,8 @@ private Task CallOnParametersSetAsync()
             Task.CompletedTask;
     }
 
+    // We do not want the debugger to stop more than once per user-unhandled exception.
+    [DebuggerDisableUserUnhandledExceptions]
     private async Task CallStateHasChangedOnAsyncCompletion(Task task)
     {
         try

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

@@ -1039,6 +1039,8 @@ async Task ContinueAfterTask(ArrayRange<ulong> eventHandlerIds, Task afterTaskIg
         }
     }
 
+    // We do not want the debugger to stop more than once per user-unhandled exception.
+    [DebuggerDisableUserUnhandledExceptions]
     private async Task GetErrorHandledTask(Task taskToHandle, ComponentState? owningComponentState)
     {
         try

src/Components/Components/src/Rendering/ComponentState.cs

@@ -87,6 +87,8 @@ public ComponentState(Renderer renderer, int componentId, IComponent component,
 
     internal Renderer Renderer => _renderer;
 
+    // We do not want the debugger to consider NavigationExceptions caught by this method as user-unhandled.
+    [DebuggerDisableUserUnhandledExceptions]
     internal void RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment, out Exception? renderFragmentException)
     {
         renderFragmentException = null;
@@ -106,6 +108,11 @@ internal void RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment re
         }
         catch (Exception ex)
         {
+            if (ex is not NavigationException)
+            {
+                Debugger.BreakForUserUnhandledException(ex);
+            }
+
             // If an exception occurs in the render fragment delegate, we won't process the diff in any way, so child components,
             // event handlers, etc., will all be left untouched as if this component didn't re-render at all. The Renderer will
             // then forcibly clear the descendant subtree by rendering an empty fragment for this component.

src/Components/Endpoints/src/Rendering/EndpointHtmlRenderer.Streaming.cs

@@ -77,10 +77,6 @@ public async Task SendStreamingUpdatesAsync(HttpContext httpContext, Task untilT
         }
         catch (Exception ex)
         {
-            // Rethrowing also informs the debugger that this exception should be considered user-unhandled unlike NavigationExceptions,
-            // but calling BreakForUserUnhandledException here allows the debugger to break before we modify the HttpContext.
-            Debugger.BreakForUserUnhandledException(ex);
-
             // Theoretically it might be possible to let the error middleware run, capture the output,
             // then emit it in a special format so the JS code can display the error page. However
             // for now we're not going to support that and will simply emit a message.

src/Middleware/Diagnostics/src/DeveloperExceptionPage/DeveloperExceptionPageMiddlewareImpl.cs

@@ -102,13 +102,8 @@ private static void SetExceptionHandlerFeatures(ErrorContext errorContext)
     /// </summary>
     /// <param name="context"></param>
     /// <returns></returns>
-    [DebuggerDisableUserUnhandledExceptions]
     public async Task Invoke(HttpContext context)
     {
-        // We want to avoid treating exceptions as user-unhandled if an exception filter like the DatabaseDeveloperPageExceptionFilter
-        // handles the exception rather than letting it flow to the default DisplayException method. This is because we don't want to stop the
-        // debugger if the developer shouldn't be handling the exception and instead just needs to do something like click a link to run a
-        // database migration.
         try
         {
             await _next(context);
@@ -127,11 +122,6 @@ public async Task Invoke(HttpContext context)
                     context.Response.StatusCode = StatusCodes.Status499ClientClosedRequest;
                 }
 
-                // Generally speaking, we do not expect application code to handle things like IOExceptions during a request
-                // body read due to a client disconnect. But aborted requests should be rare in development, and developers
-                // might be surprised if an IOException propagating through their code was not considered user-unhandled.
-                // That said, if developers complain, we consider removing the following line.
-                Debugger.BreakForUserUnhandledException(ex);
                 return;
             }
 
@@ -141,8 +131,6 @@ public async Task Invoke(HttpContext context)
             {
                 _logger.ResponseStartedErrorPageMiddleware();
                 _metrics.RequestException(exceptionName, ExceptionResult.Skipped, handler: null);
-
-                // Rethrowing informs the debugger that this exception should be considered user-unhandled.
                 throw;
             }
 
@@ -173,16 +161,11 @@ public async Task Invoke(HttpContext context)
             }
             catch (Exception ex2)
             {
-                // It might make sense to call BreakForUserUnhandledException for ex2 after we do the same for the original exception.
-                // But for now, considering the rarity of user-defined IDeveloperPageExceptionFilters, we're not for simplicity.
-
                 // If there's a Exception while generating the error page, re-throw the original exception.
                 _logger.DisplayErrorPageException(ex2);
             }
 
             _metrics.RequestException(exceptionName, ExceptionResult.Unhandled, handler: null);
-
-            // Rethrowing informs the debugger that this exception should be considered user-unhandled.
             throw;
         }
 
@@ -195,9 +178,6 @@ public async Task Invoke(HttpContext context)
     // Assumes the response headers have not been sent.  If they have, still attempt to write to the body.
     private Task DisplayException(ErrorContext errorContext)
     {
-        // We need to inform the debugger that this exception should be considered user-unhandled since it wasn't fully handled by an exception filter.
-        Debugger.BreakForUserUnhandledException(errorContext.Exception);
-
         var httpContext = errorContext.HttpContext;
         var headers = httpContext.Request.GetTypedHeaders();
         var acceptHeader = headers.Accept;