More conhost exceptions via SetConsoleScreenBufferSize

[j4james]

Environment

Windows build number: Version 10.0.18363.1198
Windows Terminal version (if applicable): Commit 6213172

Steps to reproduce

1. Start a conhost cmd shell.
2. Open the properties and make sure Wrap text output on resize is unchecked.
3. Compile and run the program below.

#include <windows.h>
int main()
{
	HANDLE h = GetStdHandle(STD_OUTPUT_HANDLE);
	COORD coord;
	coord.X = 160;
	coord.Y = 100;
	SetConsoleScreenBufferSize(h, coord);
	SMALL_RECT r = { 80, 75, 159, 99 };
	SetConsoleWindowInfo(h, TRUE, &r);
	SetConsoleCursorPosition(h, { 159, 99 });
	coord.X = 80;
	SetConsoleScreenBufferSize(h, coord);
	return 0;
}

Expected behavior

The conhost instance shouldn't crash and there shouldn't be any exceptions logged in the debug output.

Actual behavior

On my current version of Windows the conhost instance crashes. On the latest version of OpenConsole the exception is caught, so it at least doesn't crash, but you can see the error being logged in the debug output.

This is essentially the same bug as #1976, only the overflow is horizontal rather than vertical. It should have been fixed by PR #8309, but I managed to screw that up. I mistakenly thought the Viewport::EndExclusive method returned the bottom right extent of the viewport, but it's actually returning { Left(), BottomExclusive() }, so the overflow calculation doesn't detect a horizontal overflow. See here:

terminal/src/host/getset.cpp

Lines 530 to 531 in d09fdd6

	// Make sure the viewport doesn't now overflow the buffer dimensions.
	auto overflow = screenInfo.GetViewport().EndExclusive() - screenInfo.GetBufferSize().Dimensions();

and here:

terminal/src/types/viewport.cpp

Lines 148 to 151 in ae550e0

	COORD Viewport::EndExclusive() const noexcept
	{
	return { Left(), BottomExclusive() };
	}

The fix is easy enough. I'd probably just add something like an ExclusiveExtent method to the Viewport class that returns the range I was actually excepting to get from Viewport::EndExclusive. Does that seem reasonable?

[zadjii-msft]

Yea that seems sensible to me. Thanks for investigating and putting the fix together!