[iOS] System.Diagnostics.Debug.Assert causing app to crash

[i-nikityuk]

Apple platform

iOS

Framework version

net8.0-*

Affected platform version

VS For Mac 17.6.14 / Rider 2024.3.6

Description

Reality:
Call Debug.Assert(false, "Message text"); from AppDelegate or any other place in the iOS app (mine is NET8, NOT MAUI) - app will crash (if debugger is not attached)

Expectations:
app will continue execution without a crash

Steps to Reproduce

1. Create new empty iOS app
2. call Debug.Assert(false, "Message text"); from any place
3. Run app without debugger attached
4. app will crash
5. if debugger is attached app will continue execution with console output similar to this:

---- DEBUG ASSERTION FAILED ----
---- Assert Short Message ----
Message text
---- Assert Long Message ----

at System.Diagnostics.DefaultTraceListener.Fail(String message, String detailMessage)
at System.Diagnostics.TraceInternal.Fail(String message, String detailMessage)
at System.Diagnostics.TraceInternal.TraceProvider.Fail(String message, String detailMessage)
at System.Diagnostics.Debug.Fail(String message, String detailMessage)
at System.Diagnostics.Debug.Assert(Boolean condition, String message, String detailMessage)
at System.Diagnostics.Debug.Assert(Boolean condition, String message)
....... removed.
NOTE: this is not a crash ^^ - it is just output of "new StackTrace(bool fNeedFileInfo).ToString()" called internally in "DefaultTraceListener.Fail"

Did you find any workaround?

WORKAROUND:
As Debug.Assert using "DefaultTraceListener" by default, setting "AssertUiEnabled" property to false fixed the issue.

DefaultTraceListener traceListener = new DefaultTraceListener();
traceListener.AssertUiEnabled = false;

Trace.Listeners.Clear();
Trace.Listeners.Add(traceListener);

Relevant logs

Issue looks identical or at least very close to this issue, despite being on another platform
#40512

[rolfbjarne]

This behavior comes from here:

runtime/src/libraries/System.Private.CoreLib/src/System/Diagnostics/DebugProvider.Unix.cs

Lines 18 to 29 in 98b365d

	if (Debugger.IsAttached)
	{
	Debugger.Break();
	}
	else
	{
	// In Core, we do not show a dialog.
	// Fail in order to avoid anyone catching an exception and masking
	// an assert failure.
	DebugAssertException ex = new DebugAssertException(message, detailMessage, stackTrace);
	Environment.FailFast(ex.Message, ex, errorSource);
	}

so it looks intentional.

That said, what would you expect the behavior to be?

In any case, moving to dotnet/runtime, since that's where the code in question resides.

[filipnavara]

That sounds intentional to me, it's the normal behavior on desktop platforms too. The asserts are compiled-out in Release builds.

[i-nikityuk]

Thank you for your response guys.

My expectations were:

In Release builds - asserts are compiled-out. (all good here)

In Debug builds:

if (Debugger.IsAttached)
{
// Exactly the behaviour I would expect, stop debugger on Assert call
Debugger.Break(); // All good here
}
else
{
// However, here I would expect just console output without
// terminating the app
}

=====================================================

After reading comments in @rolfbjarne response ("Fail in order to avoid anyone catching an exception and masking an assert failure.") I think it all make sense and just my assumptions/expectations of Debug.Assert were incorrect.

Thanks once again, close it.