refac(prog/nvim): enable folding for rust,js,ts

programs/nvim/init.vim

@@ -35,13 +35,6 @@ aug filetype_md
 aug END
 " }}}
 
-" Vimscript file settings {{{
-aug filetype_vim
-  au!
-  au FileType vim setlocal foldmethod=marker foldcolumn=1 foldlevelstart=0
-aug END
-" }}}
-
 " Plugins {{{
 call plug#begin()
   Plug 'junegunn/seoul256.vim'                        " theme

programs/nvim/plugins/base-fold-opt.vim

@@ -0,0 +1,22 @@
+aug config_fold
+  au!
+  au FileType * call <SID>ConfigFold()
+aug END
+
+function! s:ConfigFold()
+  let l:ft = &g:filetype
+
+  if l:ft ==# 'vim'
+    call <SID>SetlFold('marker', 0)
+  elseif l:ft ==# 'markdown'
+    return
+  else
+    call <SID>SetlFold('syntax', 99)
+  endif
+endfunction
+
+function! s:SetlFold(method, lvl)
+  let &foldmethod = a:method
+  let &foldlevel = a:lvl
+  let &foldcolumn = 1
+endfunction