Win32 input make/break events are generated at the same time

[o-sdn-o]

Environment

Windows build number: 10.0.19041.572
Windows Terminal version (if applicable): master

In the classic windows console, you can track alphanumeric key combinations (for example, tracking the keys w, a, s, d simultaneously). This tracking cannot be done in Windows Terminal.

Steps to reproduce

Run the following code
Press a couple of alphanumeric keys at the same time, e.g. q+w+e

#include <iostream>
#include <unordered_set>
#include <Windows.h>

int main()
{
    DWORD                    Count;
    INPUT_RECORD             Reply;
    std::unordered_set<WORD> State;

    auto Input = GetStdHandle(STD_INPUT_HANDLE);

    while (WAIT_OBJECT_0 == WaitForSingleObject(Input, INFINITE))
    {
        ReadConsoleInput(Input, &Reply, 1, &Count);
        switch (Reply.EventType)
        {
            case KEY_EVENT:
            {
                //std::cout
                //    << " Down: "     << Reply.Event.KeyEvent.bKeyDown
                //    << " Repeat: "   << Reply.Event.KeyEvent.wRepeatCount
                //    << " KeyCode: "  << Reply.Event.KeyEvent.wVirtualKeyCode
                //    << " ScanCode: " << Reply.Event.KeyEvent.wVirtualScanCode
                //    << " Char: "     << Reply.Event.KeyEvent.uChar.UnicodeChar
                //    << " KeyState: " << Reply.Event.KeyEvent.dwControlKeyState
                //    << std::endl << std::flush;

                auto ScanCode = Reply.Event.KeyEvent.wVirtualScanCode;
                auto KeyDown = Reply.Event.KeyEvent.bKeyDown;
                auto Changed = KeyDown ? State.emplace(ScanCode).second
                                       : State.erase(ScanCode);
                if (Changed)
                {
                    std::cout << "chord:";
                    for (auto Key : State) std::cout << " " << Key;
                    std::cout << std::endl << std::flush;
                }
                break;
            }
            default:
                break;
        }
    }
}

Expected behavior

Key combinations are tracked (classic console behavior)

D:\sources\temp\ConsoleApplication1\Debug>ConsoleApplication1.exe
chord: 16
chord: 16 17
chord: 16 17 18
chord: 16 17
chord: 16
chord:
chord: 16
chord: 16 17
chord: 16 17 18
chord: 17 18
chord: 18
chord:

Actual behavior

Single keystrokes are tracked only (Windows Terminal behavior)

D:\sources\temp\ConsoleApplication1\Debug>ConsoleApplication1.exe
chord: 16
chord:
chord: 17
chord:
chord: 18
chord:
chord: 18
chord:
chord: 18
chord:
chord: 18
chord:
chord: 18
chord:
...

[zadjii-msft]

Yep, this is unfortunately true. Since the Terminal is using the UWP XAML Input stack, we only get three types of input events: key downs, key ups, and character received events. Since we don't get full unicode character input from just the key down/ups, we have to rely on the character events for that. But there's no character up/down events, only received. So we've got to send a fake key down/up pair immediately. I'm sure if there was a way to avoid doing this, @lhecker would have thought of it by now 😜

For the sake of linking: #4999 dealt with a lot of similar issues. At least conpty is now capable of theoretically handling this, if only the Terminal was.

[lhecker]

We could integrate the UWP based WT more deeply with our Win32 entrypoint.
That would allow us to use something like our old approach documented here.

[DHowett]

I've renamed this and iceboxed it. There's some ways in which we'll want to be compatible with the console, and a great many in which we will not.

This one requires enough work (and subversion of the "modern" input stack) that I would bin it into the "not" category, but... that's me.