App stdout leaks to XHarness stderr

[premun]

Part of the stdout that is the app writing and is received in XHarness through the TCP listener is displayed in stdout of XHarness. Only stuff logged through ILogger should be displayed.

Actual:

info: test[0]
      Starting test for ios-simulator-64..
info: test[0]
      Starting application 'System.Numerics.Vectors.Tests' on ios-simulator-64
2020-04-28 03:44:30.671603-0700 System.Numerics.Vectors.Tests[40307:10721880] assembly_preload_hook: System.Private.CoreLib (null) /Users/prvysoky/Library/Developer/CoreSimulator/Devices/1CE4848E-D84A-4600-84AA-3F04A42F2046/data/Containers/Bundle/Application/F91EA8BA-4A19-4EEB-880B-107D5DFE3471/System.Numerics.Vectors.Tests.app
2020-04-28 03:44:30.697425-0700 System.Numerics.Vectors.Tests[40307:10721880] assembly_preload_hook: AppleTestRunner.dll (null) /Users/prvysoky/Library/Developer/CoreSimulator/Devices/1CE4848E-D84A-4600-84AA-3F04A42F2046/data/Containers/Bundle/Application/F91EA8BA-4A19-4EEB-880B-107D5DFE3471/System.Numerics.Vectors.Tests.app
...

Expected:

info: test[0]
      Starting test for ios-simulator-64..
info: test[0]
      Starting application 'System.Numerics.Vectors.Tests' on ios-simulator-64

[premun]

So it looks like the output is in &2, so 2>/dev/null fixes this, but still looking how it gets there

[premun]

I will have another stab at this one - it pains me so much that I cannot figure it out..

[mandel-macaque]

Confirmed this with the latests master when running on the simulator. Does not happen on device.

[premun]

I originally thought it is happening because of these lines:

xharness/src/Microsoft.DotNet.XHarness.iOS/AppRunner.cs

Lines 238 to 249 in 7f79598

	var stderrTty = _helpers.GetTerminalName(2);
	if (!string.IsNullOrEmpty(stderrTty))
	{
	args.Add(new SetStderrArgument(stderrTty));
	}
	else
	{
	stdoutLogPath = _logs.CreateFile($"mlaunch-stdout-{_helpers.Timestamp}.log", "Standard output");
	stderrLogPath = _logs.CreateFile($"mlaunch-stderr-{_helpers.Timestamp}.log", "Standard error");
	args.Add(new SetStdoutArgument(stdoutLogPath));
	args.Add(new SetStderrArgument(stderrLogPath));
	}

In Xamarin, there was also redirection of stdout argument to the stdout. I removed that and now everything is sent to our stderr, which would correspond with the SetStderrArgument part BUT in every run, the mlaunch stdout/err files are created which means the second branch happens.

And also based on ProcessManager, everything should be redirected to the Log that is supplied.

[premun]

Another observation:

If I call dotnet xharness ios test ... 2>/dev/null this goes away, however, if I call it with 2>foo.txt then foo.txt will be an empty file