Step becomes a "go" in .NET 9

[gregg-miskelly]

Description

.NET 9 contains a regression where ICorDebugStepper's are not always firing. The issue is non-deterministic, and causes intermittent failures in our debugging tests, and we have had a few customers reports of the problem.

Reproduction Steps

A Microsoft employee can reproduce this problem by:

1. Enlisting in the 'Concord' repo
2. Following instructs in '/glass.md' for setting up a local test environment
3. Open Test Explorer
4. Enter “CSAsyncStepOverinTryBlock-NetCore-Latest-x64” in the filter box
5. Navigate to the test
6. Right click and invoke “Run Until Failure”

Expected behavior

Stepper should complete

Actual behavior

Stepper sometimes fails to detect when it is complete and this the debugger behaves as if there was no stepper

Regression?

This regressed between .NET 8 and .NET 9

Known Workarounds

None

Configuration

So far all of the reports are from Windows, but I don't know if this is actually a causal connection.
We have at least mostly seen this on x64, but again, I am not sure if that is actually a causal connection or just because that is the most frequent configuration

Other information

No response

[dotnet-policy-service]

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[f2bo]

I'm seeing this all the time. I hadn't seen this issue before. I reported the problem here a few days ago: https://developercommunity.visualstudio.com/t/Single-stepping-is-broken-when-targettin/10802855.

I can reproduce it with the following simple steps:

• Create a new Console App project that targets .NET 8.

• Replace the contents of Program.cs with the following code:

  foreach (Range range in new Range[5])
  {
     Console.WriteLine($"{range.Start}, {range.End}");
  }

• Execute in the debugger by using Step Over (F10) or Step Into (F11) to verify that the debugger is able to single-step through each line in the program correctly.

• Change the project file to target .NET 9.

• Execute again with Step Over (F10) or Step Into (F11) . Notice that single-stepping no longer advances to the next line as expected, but that execution suddenly continues without breaking, as if F5 had been pressed.

NOTE: This behavior is erratic, so you may need to repeat a few times if it seems to work correctly.

[geoffrey-gaspari]

Same problem here.