How to yank current cmdline?

[amerlyq]

With default / I used next mapping to yank current cmdline directly from cmdline:

function! CopyStringInReg(r, str)
 " Preserve previous buffer in register.
  call setreg('p', getreg(a:r, 1),  getregtype(a:r))
  call setreg(a:r, a:str, getregtype(a:r))
  call CountLinesInRegister(a:r, '@'. a:r .':')
endfunction
cnoremap <C-y> <C-R>=CopyStringInReg('+', getcmdline())<CR><C-H>

How can I do something similar from inside incsearch.vim fake cmdline?
I know there is something like cli-remapping. But this don't work:

  let g:incsearch_cli_key_mappings = { "\<C-y>": {
        \ 'key': "\<C-r>=CopyStringInReg('+',incsearch#cli()._pattern)\<CR>\<C-h>",
        \ 'noremap': 1 }}

I haven't found any useful field inside incsearch#cli() dict, which I could use instead of getcmdline().
Any useful suggestions/alternatives are very desirable.