Change latex provider to luatex, closes #476

autoload/vimtex/fold/preamble.vim

@@ -0,0 +1,36 @@
+if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'latex') == -1
+
+" vimtex - LaTeX plugin for Vim
+"
+" Maintainer: Karl Yngve Lervåg
+" Email:      karl.yngve@gmail.com
+"
+
+function! vimtex#fold#preamble#new(config) abort " {{{1
+  return extend(deepcopy(s:folder), a:config)
+endfunction
+
+" }}}1
+
+
+let s:folder = {
+      \ 'name' : 'preamble',
+      \ 're' : {
+      \   'start' : '^\s*\\documentclass',
+      \   'fold_re' : '\\documentclass',
+      \ },
+      \}
+function! s:folder.level(line, lnum) abort dict " {{{1
+  if a:line =~# self.re.start
+    return '>1'
+  endif
+endfunction
+
+" }}}1
+function! s:folder.text(line, level) abort dict " {{{1
+  return '      Preamble'
+endfunction
+
+" }}}1
+
+endif