augroup VCSCommand
  autocmd User VCSBufferCreated call s:vcs_buffer_created()
augroup END

function! s:vcs_buffer_created()
  if b:VCSCommandCommand ==# 'commitlog'
    call cursor('$', 1)
    delete _
    call append('$', b:VCSCommandSourceFile . ': ')
    call cursor('$', '$')
    startinsert!
  endif
endfunction