Changing foldmarker per filetype with vim 8.2

Question

On an up-to-date Arch system, I set up marker-based folds in vim and python scripts like so:

Extracted from my ~/.vimrc [1]

set nocompatible  " default
filetype plugin indent on
set nofoldenable
set foldlevel=1
set foldcolumn=1

Along with:

$ cat ~/.vim/after/ftplugin/vim.vim
setlocal foldmethod=marker
setlocal foldmarker={{{,}}}  " Default for fdm=marker

$ cat ~/.vim/after/ftplugin/python.vim
setlocal foldmethod=marker
setlocal foldmarker={{{,}}}  " Default for fdm=marker
setlocal foldnestmax=3

It works for vim scripts but not for python. I've been at it most of one day already and frankly I am missing something. I am currently resorting to committing the content of ~/.vim/after/ftplugin/python.vim directly to ~/.vimrc and setting the corresponding parameters globally instead of locally. That works well, but that also excludes the possibility of differentiating settings, e.g.:

• marker-based folds in vim
• indent-based or syntax-based folds in python or in bash scripts.

What am I doing wrong ?

---

With all setting committed globaly to ~/.vimrc, what I get in the vim buffer of any python module is:

: verbose set filetype? foldmethod? foldmarker?
      filetype=python
            Last set from /usr/share/vim/vim82/filetype.vim line 1291                                                      
      foldmethod=marker
            Last set from ~/.vim/view/~=+Documents=+Work=+Projects=+xxx-data=+Src=+proof_demo.py= line 67
      foldmarker={{{,}}}
            Last set from ~/.vim/view/~=+Documents=+Work=+Projects=+xxx-data=+Src=+proof_demo.py= line 66 

---

What "it doesn't work" means

It doesn't fold at all when I do zc, other than where I have previously set fold(s) manually. zM has no effect at all (for example when foldmethod=indent in ~/.vim/after/ftplugin/python.vim), again except when markers are set manually (provided foldmethod=marker in ~/.vimrc). Same behavior for all python files, which tells me it is probably some deep-seated issue, not malformed python file. Same in shell scripts with a similarly built ~/.vim/after/ftplugin/sh.vim, so it's not python specific.

Views info

The most interesting use case in that context is when foldmethod=manual because, without views, manually set folds are lost upon closing the buffer. But I need views to be able to go back to the buffer's last cursor position (line + col) when re-opening a file with vim. I need views for that because the alternative I did implement before I started using folds, based on vim.fandom.com/wiki/…, is incompatible with implementing any kind of folds apparently. It just fails silently.

It turns out my use of "views" is not compatible with parsing settings from ~/.vim/after/ftplugin/*.vim files. "Why ?" is beyond me. I am not sure whether it is the execution context I build by means of my ~/.vimrc or a bug. I would tend to favor the first, although I really don't have much special in ~/.vimrc.

Answer 1

[Thanks to @DBenKnoble for his insight. It led me right to the solution.]

When using "views" to store vim sessions snapshots, watch for the value(s) of the vop option parameter. For more info :h vop. Its default is:

set viewoptions=cursor,folds,options,curdir

Use of folds in the above conflicts with the use of ~/.vim/after/ftplugin/*.vim files. You can take foldsout and go on using the two autocmd lines below in your ~/.vimrc. Both call on "views":

au BufWinLeave * mkview
au VimEnter * silent loadview

Then you can go back to using ~/.vim/after/ftplugin/python.vim as you did. You can check that for any python module:

:verbose set filetype? foldmethod? foldmarker?
    filetype=python
         Last set from /usr/share/vim/vim82/filetype.vim line 1291
    foldmethod=marker
         Last set from ~/.vim/view/~=+.vimrc line 67
    foldmarker={{{,}}}
         Last set from ~/.vim/view/~=+.vimrc line 65

So the best thing is to stick to views and just suppress the folds option in viewoptions in your ~/.vimrc:

set viewoptions=cursor,options,curdir