CMD + SHIFT mappings are inconsistent

[fredizzimo]

Problem

CMD + SHIFT mappings behave differently from other mappings like ALT + SHIFT and are not normalized to a standard format. The reason seems to be this line, which I have found no explanation for

neovim/src/nvim/keycodes.c

Line 774 in 6e26964

if (!(modifiers & MOD_MASK_CMD) && !(modifiers & MOD_MASK_CTRL)) {

This also makes mappings between different Neovim GUIs inconsistent, since each of them reports the mappings slightly differently to Neovim.

NOTE: I'm aware that the CTRL mappings behaves differently due to legacy reasons, and it's also clear why the CTRL condition is there. But not why the condition is there for CMD.

Steps to reproduce

1. Create a file mappings.vim with the following contents

map <D-a> <cmd>:echomsg "D-a"<cr>
map <D-A> <cmd>:echomsg "D-A"<cr>
map <D-S-a> <cmd>:echomsg "D-S-a"<cr>
map <D-S-A> <cmd>:echomsg "D-S-A"<cr>

map <M-a> <cmd>:echomsg "M-a"<cr>
map <M-A> <cmd>:echomsg "M-A"<cr>
map <M-S-a> <cmd>:echomsg "M-S-a"<cr>
map <M-S-A> <cmd>:echomsg "M-S-A"<cr>

map <C-a> <cmd>:echomsg "C-a"<cr>
map <C-A> <cmd>:echomsg "C-A"<cr>
map <C-S-a> <cmd>:echomsg "C-S-a"<cr>
map <C-S-A> <cmd>:echomsg "C-S-A"<cr>

call feedkeys("\<D-a>")
call feedkeys("\<D-A>")
call feedkeys("\<D-S-a>")
call feedkeys("\<D-S-A>")

call feedkeys("\<M-a>")
call feedkeys("\<M-A>")
call feedkeys("\<M-S-a>")
call feedkeys("\<M-S-A>")

call feedkeys("\<C-a>")
call feedkeys("\<C-A>")
call feedkeys("\<C-S-a>")
call feedkeys("\<C-S-A>")

2. Run nvim --clean -u mappings.vim
3. Type :messages
4. Observe that the following output was generated

D-a
D-A
D-S-a
D-S-A
M-a
M-S-A
M-S-A
M-S-A
C-A
C-A
C-S-A
C-S-A

Expected behavior

The output should be:

D-a
D-S-A
D-S-A
D-S-A
M-a
M-S-A
M-S-A
M-S-A
C-A
C-A
C-S-A
C-S-A

Making the D and M mappings consistent, and select the last shift combination that was mapped.

Neovim version (nvim -v)

NVIM v0.9.2

Vim (not Nvim) behaves the same?

N/A

Operating system/version

Arch Linux (WSL)

Terminal name/version

Windows Terminal

$TERM environment variable

xterm-256color

Installation

pacman