Detect macOS Dark Mode

[shaunlebron]

Recommending that we copy MacVim to allow changing colorscheme when macOS dark mode is toggled: https://github.com/macvim-dev/macvim/pull/929

It adds a OSAppearanceChanged event and a v:os_appearance var:

" inside ~/.vimrc

func! ChangeBackground()
  if (v:os_appearance == 1)
    set background=dark
    colorscheme onedark
  else 
    set background=light
    colorscheme bclear
  endif
  redraw!
endfunc

if has("gui_vimr")
  call ChangeBackground()
  au OSAppearanceChanged * call ChangeBackground()
endif

[bmulholland]

In the meantime, I use dark-notify for that.

[qvacua]

This is a good idea.