A command using FZF that takes a range to list only those files altered in last <range> commits

fzf.vim

" A command using FZF to list all files in a Git repo; 
" takes a range 0, N or N,M to restrict to files that have been, respectively, 
" altered, altered in last N commits, altered in-between last N and M commits.

" From https://github.com/junegunn/fzf.vim/blob/879db51d0965515cdaef9b7f6bdeb91c65d2829e/autoload/fzf/vim.vim#L742
function! s:get_git_root(dir)
  if empty(a:dir) && exists('*FugitiveWorkTree')
    return FugitiveWorkTree()
  endif
  let dir = len(a:dir) ? a:dir : substitute(split(expand('%:p:h'), '[/\\]\.git\([/\\]\|$\)')[0], '^fugitive://', '', '')
  let root = systemlist('git -C ' . shellescape(dir) . ' rev-parse --show-toplevel')[0]
  return v:shell_error ? '' : (len(a:dir) ? fnamemodify(a:dir, ':p') : root)
endfunction
" Returns the path to bash executable, or empty string if not found.
function! s:bash() abort
  if has('win32')
    " On Windows, prefer Git Bash or WSL bash.
    let git_bash = $ProgramFiles . '\Git\bin\bash.exe'
    if filereadable(git_bash) | return git_bash | endif
    if executable('bash') | return 'bash' | endif
    return ''
  else
    " On Unix, just use 'bash' if available.
    return executable('bash') ? 'bash' : ''
  endif
endfunction
" Escapes a path for safe usage in bash -c "...".
function! s:bash_quote(str) abort
  return "'" . substitute(a:str, "'", "'\"'\"'", 'g') . "'"
endfunction
function! s:escape_for_bash(path) abort
  if has('win32')
    let p = a:path
    let p = substitute(p, '^\(\a\):\\', '/mnt/\L\1/', '')
    let p = substitute(p, '\\', '/', 'g')
    return s:bash_quote(p)
  endif
  return s:bash_quote(a:path)
endfunction

function! s:GitFiles(bang, range, count, args) abort range
  let root = s:get_git_root('')

  " No explicit range means original behavior.
  if a:range == 0
    if empty(root)
      return fzf#run(fzf#wrap('FZF'))
    endif
    return fzf#vim#gitfiles(a:args, fzf#vim#with_preview({}), a:bang)
  endif

  " Any explicit range requires a git worktree.
  if empty(root)
    echom getcwd() . ' is not in a git repository'
    return 0
  endif

  " Single-item range :0GitFiles means :GFiles? behavior.
  if a:range == 1 && a:count == 0
    return fzf#vim#gitfiles('?', fzf#vim#with_preview({ 'placeholder': '' }), a:bang)
  endif

  let n = a:firstline
  let m = a:lastline

  if n < 1 || m < 1
    echom 'GitFiles range values must be >= 1'
    return 0
  endif

  let filter = has('win32') ? 'findstr /v "^$"' : 'sed -e /^$/d'

  " Compute revision endpoints.
  if a:range == 1
    let rev_from = 'HEAD~' . n
    let rev_to   = 'HEAD'
    let source   = 'git log HEAD --max-count=' . n . ' --diff-filter=MA --name-only --pretty=format: | ' . filter
  else
    " Ex ranges generally enforce n <= m, but keep swapping for robustness.
    if n > m
      let [n, m] = [m, n]
    endif
    let rev_from = (m == 0 ? 'HEAD' : 'HEAD~' . m)
    let rev_to   = (n == 0 ? 'HEAD' : 'HEAD~' . n)
    let source   = 'git log ' . rev_from . '..' . rev_to . ' --diff-filter=MA --name-only --pretty=format: | ' . filter
  endif

  let prompt = 'GitFiles(' . rev_from . '..' . rev_to . ')> '
  let opts = ['--scheme', 'path', '--prompt', prompt]

  " Preview uses bash for consistent quoting and optional delta rendering.
  if executable('git') && executable(s:bash())
    let bar = has('win32') ? '^|' : '|'
    let diff_prefix = 'git -C ' . s:escape_for_bash(root) . ' '

    if executable('delta')
      let diff =
            \ diff_prefix
            \ . 'diff --color=always ' . rev_from . '..' . rev_to . ' -- {-1} '
            \ . bar . ' delta --width $FZF_PREVIEW_COLUMNS --file-style=omit '
            \ . bar . ' sed 1d'
    else
      let diff =
            \ diff_prefix
            \ . 'diff --color=always ' . rev_from . '..' . rev_to . ' -- {-1} '
            \ . bar . ' sed 1,4d'
    endif

    let preview_cmd = s:bash() . ' -c "' . diff . '"'
    call extend(opts, ['--preview', preview_cmd, '--preview-window', 'right,50%,<70(up,40%)'])
  endif

  return fzf#run(fzf#wrap('gitfiles', {
        \ 'source':  source,
        \ 'dir':     root,
        \ 'options': opts,
        \ }))
endfunction
command! -bang -range=0 -nargs=? GitFiles <line1>,<line2>call s:GitFiles(<bang>0, <range>, <count>, <q-args>)