commit https://github.com/vim/vim/commit/864293abb72d62604d8d6b458addfb43c14230c3 Author: Bram Moolenaar <Bram@vim.org> Date: Thu Jun 2 13:40:04 2016 +0200 patch 7.4.1871 Problem: Appending to the quickfix list while the quickfix window is open is very slow. Solution: Do not delete all the lines, only append the new ones. Avoid using a window while updating the list. (closes #841)

" Vim filetype plugin file
" Language:         m4
" Maintainer:       Nikolai Weibull <now@bitwi.se>
" Latest Revision:  2008-07-09

if exists("b:did_ftplugin")
  finish
endif
let b:did_ftplugin = 1

let s:cpo_save = &cpo
set cpo&vim

let b:undo_ftplugin = "setl com< cms< fo<"

setlocal comments=:#,:dnl commentstring=dnl\ %s
setlocal formatoptions-=t formatoptions+=croql

let &cpo = s:cpo_save
unlet s:cpo_save