Clear Buffer is broken in Windows Terminal Preview (1.22.2362.0)

[valiko-ua]

Windows Terminal version

1.22.2362.0

Windows build number

10.0.22631.4037

Steps to reproduce

• Settings -> Actions -> Add New -> Add "Ctrl+l" (lowercase L) for "Clear Buffer". Press Save.
• Open tab with "Command Prompt".
• Execute "cd C:\Windows". Execute "dir" several times to fill the screen.
• Press Ctrl+l (lowercase L).

Expected Behavior

Clear Buffer works fine in Windows Terminal v.1.20.11781.0.

Actual Behavior

Clear Buffer does not work in Windows Terminal Preview v.1.22.2362.0.

The same problem can be reproduced with "Ubuntu 24.04 LTS" tab (WSL2).

I've just noticed that pressing Ctrl+Shift+L works differently from Ctrl+L (but still broken). And I didn't assign Ctrl+Shift+L to anything.

[zadjii-msft]

@lhecker Didn't we fix this during the original #17510? I could have swore that I filed that, but I can't find it now

[elsaco]

@valiko-ua it's not the key binding. In 1.22.2362 the Clear buffer doesn't work. Fill the buffer with data and invoke the command via ctrl+shift+p. It won't clear the buffer!

[j4james]

I think the problem is explained by the comment here:

terminal/src/cascadia/TerminalControl/ControlCore.cpp

Lines 2232 to 2238 in 544452d

	// Send a signal to conpty to clear the buffer.
	if (auto conpty{ _connection.try_as<TerminalConnection::ConptyConnection>() })
	{
	// ConPTY will emit sequences to sync up our buffer with its new
	// contents.
	conpty.ClearBuffer();
	}

In the past when you asked conpty to clear its buffer, the vtengine would have pushed back an update that also cleared the buffer in the connected terminal, but that's not happening anymore. On the conhost side, the ClearBuffer signal is handled here:

terminal/src/host/PtySignalInputThread.cpp

Lines 185 to 201 in 544452d

	void PtySignalInputThread::_DoClearBuffer() const
	{
	LockConsole();
	auto Unlock = wil::scope_exit([&] { UnlockConsole(); });
	// If the client app hasn't yet connected, stash the new size in the launchArgs.
	// We'll later use the value in launchArgs to set up the console buffer
	// We must be under lock here to ensure that someone else doesn't come in
	// and set with `ConnectConsole` while we're looking and modifying this.
	if (!_consoleConnected)
	{
	return;
	}
	auto& gci = ServiceLocator::LocateGlobals().getConsoleInformation();
	THROW_IF_FAILED(gci.GetActiveOutputBuffer().ClearBuffer());
	}

Which just calls the SCREEN_INFORMATION class here:

terminal/src/host/screenInfo.cpp

Lines 2142 to 2162 in 544452d

	[[nodiscard]] HRESULT SCREEN_INFORMATION::ClearBuffer()
	{
	// Rotate the buffer to bring the cursor row to the top of the viewport.
	const auto cursorPos = _textBuffer->GetCursor().GetPosition();
	for (auto i = 0; i < cursorPos.y; i++)
	{
	_textBuffer->IncrementCircularBuffer();
	}
	// Erase everything below that point.
	RETURN_IF_FAILED(SetCursorPosition({ 0, 1 }, false));
	auto& engine = reinterpret_cast<OutputStateMachineEngine&>(_stateMachine->Engine());
	engine.Dispatch().EraseInDisplay(DispatchTypes::EraseType::ToEnd);
	// Restore the original cursor x offset, but now on the first row.
	RETURN_IF_FAILED(SetCursorPosition({ cursorPos.x, 0 }, false));
	_textBuffer->TriggerRedrawAll();
	return S_OK;
	}

That's just going to clear the conhost buffer. As far as I can see, there's nothing in that code that will emit sequences to sync it up with the terminal buffer.