`Debug.Assert` no longer shows a dialog prompt

[RussKie]

• .NET Core Version: .NET Core 3.1 onwards

• Have you experienced this same bug with .NET Framework?: No

Problem description:

System.Diagnostics.Trace.Assert and System.Diagnostics.Debug.Assert no longer trigger a dialog prompts in desktop apps. Instead apps silently silently crash unless have a debugger attached.

As discussed in dotnet/runtime#40512, the assert behavior was changed in dotnet/coreclr#20764, and no longer raises a dialog.
https://github.com/dotnet/corefx/blob/master/src/System.Diagnostics.Debug/tests/DebugTestsUsingListeners.cs#L248-L303 illustrates how to implement a custom trace listener, which may act as a basis for a fix.

Expected behavior:

No crash, and assertion dialog must appear after assert.

Minimal repro:

1. Create new WPF Core project.
2. Put System.Diagnostics.Debug.Assert(false, "test"); anywhere in the code, for example:

   protected override void OnActivated(EventArgs e)
   {
       System.Diagnostics.Debug.Assert(false, "test");
   }

[miloush]

Possibly off-topic question, who is in charge of showing the dialog box in a console application?

[danmoseley]

@miloush there is no dialog box in a console application.

WPF folks may want to follow the discussion in dotnet/winforms#3739 when considering this one.

[miloush]

@danmosemsft But there is in .NET FW. I assume the answer is in .NET Core you have to implement it yourself. But what if I reference WPF/WinForms assemblies in a console app? What if I use assemblies from both WPF and WinForms, will there be two hooks?

[danmoseley]

That depends on the design they end up with - if they both have a TraceListener, then you'd get two different codepaths, but perhaps they'd share code. This assumes they show a dialog at all, per discussion in the winforms issue.

[IrinaPykhova]

Is the any progress on this? In 2025 it still gives me bad experience. I'm absolutely ok with not showing dialog, but if debugger is not attached, why at all it fails application? I mean, if it can work in release version, why can't it work in Debug one? If someone decided that dialogs are bad and you should log it somewhere, then wouldn't it be correct to assume that application should continue execution till some exception or maybe just work if it works? And if there is exception, show something to end-user!
It's impossible to work if application just fails silently

[lindexi]

I would rather display a dialog.