Buffer content is modified unexpectedly after 'rename' action when foldmethod=expr is used

[timsofteng]

Hey. When I rename file and try to open it than fern open just empty buffer. But if I try to open it second time it opens.
Look at the screencast please.

Peek.2021-04-22.20-06.mp4

[lambdalisue]

Please write step by step procedure to reproduce the situation.

[timsofteng]

1. Open fern.
2. Change name of some not empty file.
3. Press :w.
4. Open this file. It will be empty buffer.

[lambdalisue]

I could not reproduce. Please make a minimal vimrc to reproduce.

[lambdalisue]

Kapture.2021-04-24.at.02.21.31.mp4

Kapture.2021-04-24.at.02.21.20.mp4

[windwp]

Hi this bug happen to me i use

" first i open fern
:Fern . -drawer -reveal=% -toggle<CR>
" then rename with
  nmap <buffer> cw <Plug>(fern-action-rename:split)

" after i press :w<cr> it will override the content to my current file open.
" I think it should override to my fern drawner buffer.

" sometime it work perfect but sometime this bug happen to me.

fern.mp4

[lambdalisue]

Please make a minimal vimrc and minimal descriptive steps to reproduce.
https://github.com/lambdalisue/fern.vim/wiki/Minimal-vimrc#with-native-vimneovim

[windwp]

https://gist.github.com/windwp/be22ae313538e1d6743de0d21dfaadeb
hi it is my vimrc.min
the first time
I press <c-b> rename with cw and save <c-s>.
It work correct . I close fern with <c-b> and reopen fern again with<c-b>
on second time it override my buffer.

fern.mp4

Thank.

[lambdalisue]

I'm sorry but I don't think it's minimal. Please make it minimal.

[windwp]

https://gist.github.com/windwp/be22ae313538e1d6743de0d21dfaadeb
I update it
It still happen on the second time rename.

[lambdalisue]

Thanks. It seems minimal enough 👍 I'll try it on my environment within few days but let me know your environment in case (OS, Vim or Neovim? and which version or etc.)

[lambdalisue]

Thanks. I could reproduce the issue. I'll investigate it.

[lambdalisue]

It seems foldmethod=expr is the reason. It happens on Vim (8.2.2681) and Neovim (0.5.0-dev)

vimrc

if exists('+compatible') && &compatible
  set nocompatible
endif

" Disable Vim's native pack feature
set packpath=

" Clone https://github.com/lambdalisue/fern.vim in somewhere
" and specify that directory to the below
"
set runtimepath^=~/ghq/github.com/lambdalisue/fern.vim

filetype plugin indent on
syntax on
"----------------------------------------------------------------

" Add extra settings here to reproduce the issue...
set foldmethod=expr

"----------------------------------------------------------------
echomsg "Custom minimal vimrc has loaded"

procedure

1. nvim -u ~/.vim/vimrc.min
2. Open fern by :Fern . -drawer
3. Close fern by :q
4. Open fern by :Fern . -drawer
5. Move cursor on README.md then hit R
6. Rename to Hello.md then :w

Kapture.2021-05-02.at.14.43.12.mp4