Active screen buffer size is out of sync

[o-sdn-o]

Windows Terminal version

current main branch

Windows build number

10.0.19045.3448

Other Software

No response

Steps to reproduce

• Run WT with any profile
• Run the following c++20 code (creates additional screen buffer and make it active)
• Resize the current pane (e.g., split pane)
• Press any key to exit
• Check the current size report - it is not valid
• Run any TUI app just to be sure (e.g. wsl mc )

#include <string>
#include <windows.h>

int main()
{
	auto len = DWORD{};
	auto rec = INPUT_RECORD{};
	auto inf = CONSOLE_SCREEN_BUFFER_INFO{};
	auto inp = ::GetStdHandle(STD_INPUT_HANDLE);
	auto out = ::GetStdHandle(STD_OUTPUT_HANDLE);
	auto alt = ::CreateConsoleScreenBuffer(GENERIC_READ | GENERIC_WRITE, 0, 0, CONSOLE_TEXTMODE_BUFFER, 0);
	::SetConsoleActiveScreenBuffer(alt);
	::GetConsoleScreenBufferInfo(alt, &inf);
	auto msg = "current size: " + std::to_string(inf.dwSize.X) + "x" + std::to_string(inf.dwSize.Y)
	         + "\nchange pane size and press any key\n";
	::WriteFile(alt, msg.data(), msg.size(), &len, 0);
	while (true)
	{
		::ReadConsoleInputW(inp, &rec, 1, &len);
		if (rec.EventType == KEY_EVENT && rec.Event.KeyEvent.bKeyDown) break;
		else if (rec.EventType == WINDOW_BUFFER_SIZE_EVENT)
		{
			::GetConsoleScreenBufferInfo(out /*not alt*/, &inf);
			msg = "current size: " + std::to_string(inf.dwSize.X) + "x" + std::to_string(inf.dwSize.Y) + "\n";
			::WriteFile(alt, msg.data(), msg.size(), &len, 0);
		}
	}
	::SetConsoleActiveScreenBuffer(out);
	::GetConsoleScreenBufferInfo(out, &inf);
	msg = "current size: " + std::to_string(inf.dwSize.X) + "x" + std::to_string(inf.dwSize.Y) + "\n";
	::WriteFile(out, msg.data(), msg.size(), &len, 0);
}

Expected Behavior

After run

current size: 106x20
change pane size and press any key
current size: 51x20

After exit

PS D:\sources\test\size_test\x64\Debug> .\cpp20app.exe
current size: 51x20
PS D:\sources\test\size_test\x64\Debug>

Actual Behavior

After run

current size: 106x22
change pane size and press any key
current size: 106x22

After exit (the size has not changed despite the pane split!)

PS D:\sources\test\size_test\x64\Debug> .\cpp20app.exe
current size: 106x21
PS D:\sources\test\size_test\x64\Debug>

wsl mc:

[237dmitry]

How does it reproduce without your app? I tried with `e[?1049h and `e[?1049l but could not. [console]::BufferWidth was always correct.

[o-sdn-o]

I don't know how to reproduce this without Win32 Console API.

[zadjii-msft]

Alrighty so very brief overview of the problem: When we switch back to the old screen buffer, conpty doesn't know what to do with that. Should conpty force the old buffer to the second buffer's size? (probably). Should it send a "hey I was resized message" to whatever the terminal is? (another good option, though that'll run afoul of #5094 quickly).

I'd reckon it should probably do the same thing the alt buffer does - resize the buffer to the current size as we do the swap.