Detect if Vim will exit from inside an autocmd

Question

I have a BufWritePost autocmd that I want to run every time when a buffer is written but not when Vim is about to exit.

The variable v:dying does not really help as it only indicates if Vim exists due to a signal but I also want to detect normal shutdown. So I am looking for some thing along the lines of

au BufWritePost * if ! s:do_we_quit() | Neomake | endif

but as of now I have no idea how to write the s:do_we_quit() test.

Context: The autocmd just calls :Neomake to run syntax checks and linters on my files and load them into the quickfix/location list. But that does obviously only make sense on :w and not on :wq. Normally Neomake works asynchronously but on exit it seems to me that vim hangs and waits for Neomake and then somehow it ends up in an infinite loop.

Answer 1

You're looking for QuitPre:

let s:quitting = 0
autocmd QuitPre      * let s:quitting = 1
autocmd BufWritePost * if ! s:quitting | Neomake endif

This assumes you're running a decently recent Vim (QuitPre was added in Vim 7.3.544).

You should probably post a bug report about the infinite loop.

Answer 2

Based on Sato's answer I came up with this:

let s:quitting = 0
autocmd BufWritePost *
    \ if ! s:quitting                             |
    \   Neomake                                   |
    \ elseif tabpagenr('$') > 1 || winnr('$') > 1 |
    \   let s:quitting = 0                        |
    \ endif
autocmd QuitPre * let s:quitting = 1

• s:quitting has to be reset after closing a window, otherwise Neomake will not run on the next :w anywhere.
• I can not check the window number in QuitPre as it could be anything if I :wqa
• also I really don't want to run Neomake if I close a window as I might close all further windows shortly after (before Neomake is finished) and then Neovim will still hang

Update 1

NeoVim also provides v:exiting but that is not yet set at the time BufWritePost is triggered.

Update 2

Neomake now provides a command NeomakeCancelJobs so the original problem is solved by force canceling all running jobs in VimLeave:

augroup LucNeoMake
  autocmd!
  autocmd BufWritePost * Neomake
  autocmd VimLeave * NeomakeCancelJobs
augroup END

(This is a solution to my original problem but not the the question.)