folding.vim file, for a specific filetype, is being ignored

Question

I want to write a custom fold-method file for .paul files (based on the example at Learn Vimscript the Hard Way). However, it appears that my folding.vim file is being ignored.

I'm running VIM version 8.2.1972 (on mac os 11.2.3)

• ~/.vimrc contains nothing but syntax on

• ~/.vim/filetype.vim contains

" my filetype file
        if exists("did_load_filetypes")
          finish
        endif
        augroup filetypedetect
          au! BufRead,BufNewFile *.txt         setfiletype txt
          au! BufRead,BufNewFile *.paul        setfiletype paul
        augroup END

• ~/.vim/ftplugin/paul/folding.vim contains
  set foldmethod=expr

If I do vim sadf.paul then :set ft? returns filetype=paul so the filetype detection is working.

However, :set foldmethod? returns foldmethod=manual, whereas I had expected to see foldmethod=expr.

As a test, I then changed folding.vim to contain set foldmethod=bogus to see if I would get an error when the file was processed.

However, I see no error from the =bogus statement in .vim/ftplugin/paul/folding.vim, which makes me think that the file is never being sourced/run. And, per the suggestion from Christian Brabandt, running :scriptnames confirms that ~/.vim/ftplugin/paul/folding.vim was not sourced.

Any ideas what I'm doing wrong?

Answer 1

This answer is from Matt. Copied here from his comment.

1. You should not create filetype.vim. Use ftdetect instead.
2. Must have at least filetype plugin on