Blazor: Better stacktrace for exceptions in rendering logic, including line number in Razor files

[AndreasPetersen]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

I'm new to Blazor and I'm working on an old, large and complicated Blazor component. I'm experiencing a NullReferenceException somewhere on the Razor page, but I have no idea where, because the stacktrace does not provide such information. Only that a NullReferenceException occured during rendering as described in the documentation on Rendering logic error handling.

Consider a Home component:

@page "/"

<PageTitle>Home</PageTitle>

<h1>@_greeting.ToLower()</h1>

Welcome to your new app.

@code
{
    private string? _greeting = null;
}

a appsettings.Development.json:

{
  "Logging": {
    "LogLevel": {
      "Default": "Debug",
      "Microsoft.AspNetCore": "Debug",
      "Microsoft.Hosting.Lifetime": "Debug",
      "Microsoft.AspNetCore.SignalR": "Debug"
    }
  }
}

and a Program.cs:

using MyBlazorApp.Components;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddRazorComponents()
    .AddInteractiveServerComponents();

builder.Services.AddRazorComponents(options =>
    options.DetailedErrors = true);

var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error", createScopeForErrors: true);
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

app.UseHttpsRedirection();


app.UseAntiforgery();

app.MapStaticAssets();
app.MapRazorComponents<App>()
    .AddInteractiveServerRenderMode();

app.Run();

When starting the app the following stacktrace is shown:

System.NullReferenceException: Object reference not set to an instance of an object.
   at MyBlazorApp.Components.Pages.Home.BuildRenderTree(RenderTreeBuilder __builder)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment, Exception& renderFragmentException)
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.AddToRenderQueue(Int32 componentId, RenderFragment renderFragment)
   at Microsoft.AspNetCore.Components.ComponentBase.StateHasChanged()
   at Microsoft.AspNetCore.Components.ComponentBase.CallOnParametersSetAsync()
   at Microsoft.AspNetCore.Components.ComponentBase.RunInitAndSetParametersAsync()
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.SetDirectParameters(ParameterView parameters)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderRootComponentAsync(Int32 componentId, ParameterView initialParameters)
   at Microsoft.AspNetCore.Components.HtmlRendering.Infrastructure.StaticHtmlRenderer.BeginRenderingComponent(IComponent component, ParameterView initialParameters)
   at Microsoft.AspNetCore.Components.Endpoints.EndpointHtmlRenderer.RenderEndpointComponent(HttpContext httpContext, Type rootComponentType, ParameterView parameters, Boolean waitForQuiescence)
   at Microsoft.AspNetCore.Components.Endpoints.RazorComponentEndpointInvoker.RenderComponentCore(HttpContext context)
   at Microsoft.AspNetCore.Components.Endpoints.RazorComponentEndpointInvoker.RenderComponentCore(HttpContext context)
   at Microsoft.AspNetCore.Components.Rendering.RendererSynchronizationContext.<>c.<<InvokeAsync>b__10_0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Builder.ServerRazorComponentsEndpointConventionBuilderExtensions.<>c__DisplayClass1_1.<<AddInteractiveServerRenderMode>b__1>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|7_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

I've tried enabling all the extra detailed information I could find in the Handle errors in ASP.NET Core Blazor apps documentation, but the above stacktrace is the best I could get.

While it's easy to find the exception location in the example component, for large and complicated components it is near impossible to find the error.

Describe the solution you'd like

An option that at least gives a line number in the Razor file where the exception occured.

Additional context

No response

[s-beji]

I see in your Program.cs you got a small mistake
you add the razorcomponetns 2 times wich is not right

And you can tell the server components to output detailed errors too maybe it helps but out of my experience your feature request point out a valid weakness of razor components the stack trace lacks some infos and deeper details like we are used to it

builder.Services.AddRazorComponents(options =>
           options.DetailedErrors =true)
    .AddInteractiveServerComponents(options =>
           options.DetailedErrors = true);

[AndreasPetersen]

Thanks for the suggestions @DeepWorksStudios . I applied your suggested changes, but it didn't make a difference unfortunately.

[XtremeOwnageDotCom]

Can confirm..... exception details are, well. basically useless.

System.NullReferenceException: Object reference not set to an instance of an object.
   at [YourPageName].<BuildRenderTree>b__0_1(RenderTreeBuilder __builder2)
   at Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder.AddContent(Int32 sequence, RenderFragment fragment)
   at [YourNamespace].IF.BuildRenderTree(RenderTreeBuilder builder) in [FilePath]/IF.cs:line 31
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment, Exception& renderFragmentException)

Enough information to know it failed inside of a component, but, not which instance of it, no line numbers. Nothing at all that helps narrow down anything about what happened, other then a null reference exception occurred, and that component was involved.

Edit- actually... the component referenced... wasn't even the one throwing the exception.

[SebastianToet]

Full agreed with this, currently any error occurring during server-side rendering, somewhere in the Razor code, is extremely hard to track.