Buffer scope variable not exists when run autocmd BufUnload

Question

Describe the issue

I use a vim plugin that when use Vim to open a ipynb (python notebook) file, will call system function to use jupytext create corresponding python file to enable use like, YCM to help coding. This plugin set a autocmd BufUnload for the python file buffer to delete the python file when I quit Vim .

The bug is if the current buffer in current window is not the python file when quit Vim, the python file still there after quit Vim.

To Reproduce

I turn the plugin to a minimal version just vimscript.

1. Copy file test_unload.vim to ~/.vim/plugin (content of test_unload.vim will post below) .
2. touch tt.ipynb && vim tt.ipynb
3. :e tt.c
4. :q

After above steps, their should no tt.py file on disk, but have on tt.py.

Contents of test_unload.vim

if exists("loaded_test")
  finish
endif

function! s:read_from_ipynb()  "{{{
  if expand("<afile>:e") != "ipynb"
    echo "Not an ipynb file."
    return
  endif
  let l:filename = expand("%:p")
  let l:py_file = fnamemodify(l:filename, ":r") . ".py"
  " create python file
  call system('sleep 1;echo 123 > ' . l:py_file)
  " open the py file, wipe the ipynb file
  let l:bufnr = bufnr("%")
  execute "edit " . l:py_file
  execute "bwipeout" . l:bufnr
  set filetype=python
  execute "autocmd ipynb BufUnload <buffer> call s:cleanup()"
  let b:ipynb_file = l:filename
endfunction  "}}}

function! s:cleanup()  "{{{
  if !exists("b:ipynb_file")
    echo "Not a ipynb py file."
    return
  endif
  call delete(expand("<afile>:p"))
endfunction  "}}}

augroup ipynb
  au!
  autocmd BufReadPost *.ipynb call s:read_from_ipynb()
augroup END

let loaded_test = 1

What's in vimrc:

hmanx ~ » cat .vimrc            
set hidden
hmanx ~ »

Expected behavior

tt.py deleted by autocmd BufUnload when quit Vim.

Environment:

• Vim version: 8.2.1989-2
• OS: Manjaro Linux
• Terminal: Konsole

Additional context

I found the autocmd BufUnload did triggered when quit Vim, but it returned before delete tt.py as the condition !exists("b:ipynb_file") is true.

---

Thanks in advance!

Answer 1

As you can see in :help BufUnload:

NOTE: When this autocommand is executed, the current buffer % may be different from the buffer being unloaded <afile>.

So you should use getbufvar() to access the contents of that variable for the buffer being unloaded.

if getbufvar(+expand("<abuf>"), "ipynb_file") != ""

(Using expand("<afile>") instead of +expand("<abuf>") also works.)

This depends on the variable having contents that are different from an empty string, so it's not exactly equivalent to an exists() check. If you want to check for the variable existing exactly, then pass a sentinel value (such as v:none) as the third optional argument to getbufvar() and check for it.

if getbufvar(+expand("<abuf>"), "ipynb_file", v:none) != v:none

Answer 2

The current buffer and file is behind <afile>, not %