FZF 'smart finder' buffers + files + gitwhatchanged etc. in one pane

fzf_smart_finder.lua

--  Plug 'https://github.com/vijaymarupudi/nvim-fzf'
-- nnoremap <leader>k <cmd>lua require('fzf_smart_finder').sf()<CR>
--
-- Important note: run all `nvim_fzf` functions in coroutine

local fzf = require 'fzf'.fzf
local action = require 'fzf.actions'.action

coroutine.wrap(function()
  -- items is a table of selected or hovered fzf items
  local preview_shell = action(function(items)
    -- only one item will be hovered at any time, so get the selection
    -- out and convert it to a number
    local buf = tonumber(items[1]['id'])

    -- you can return either a string or a table to show in the preview
    -- window
    return vim.api.nvim_buf_get_lines(buf, 0, -1, false)
  end)

  local buffers = vim.api.nvim_list_bufs()
  local loaded_buffers = {}
  for _, buf_id in pairs(buffers) do
    if vim.api.nvim_buf_is_loaded(buf_id) then
      local buf_name = vim.api.nvim_buf_get_name(buf_id)
      table.insert(loaded_buffers, {id = buf_id, name = buf_name})
    end
  end
  print(vim.inspect(loaded_buffers[1]))
  -- print(table.concat(loaded_buffers, "|"))

  local result = fzf(loaded_buffers, "--preview " .. preview_shell)

  if result then
    vim.cmd("buffer" .. result[1])
  end

end)()

fzf_smart_finder.vim

" FIXME: work in progress
"
" Buffers start with [B] and files start with [F] (different colors for each
" if possible)
"
" - change commands to smaller cases
" - it may be better to use fzf internals directly (if possible)

" command! -bang SmartFinder
  " \ call fzf#vim#files(<q-args>, fzf#vim#with_preview(), <bang>0)

" Sink ------------------------------

function! s:bufopen(elem)
  execute 'buffer' matchstr(a:elem, '^[ 0-9]*')
endfunction

function! s:fileopen(elem)
  execute 'edit' a:elem
endfunction

function! s:smart_finder_sink(elem)
  call s:bufopen(a:elem)
endfunction

" Source ------------------------------

function s:smart_finder_source()
  let l:buflist=BufList()
  let l:git_files=ListGitFiles()
  return l:buflist + l:git_files
endfunction

function! ListGitFiles()
  let l:git_ls = split(system('git ls-files'), '\n')
  return l:git_ls
endfunction

function! ListGitWhatChanged()
  let l:gitwhatchanged = split(system('gitwhatchanged'), '\n')
  return l:gitwhatchanged
endfunction

function! BufList()
  redir => ls
  silent ls
  redir END
  return split(ls, '\n')
endfunction

" Command ------------------------------

command! FzfSmartFinder
  \ call fzf#run(fzf#wrap({
  \ 'source': s:smart_finder_source(),
  \ 'sink': function('s:smart_finder_sink'),
  \ 'options': '-m -x +s'
  \ }))