Change latex provider to luatex, closes #476

autoload/vimtex/syntax/p/subfile.vim

@@ -0,0 +1,19 @@
+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#syntax#p#subfile#load() abort " {{{1
+  if has_key(b:vimtex_syntax, 'subfile') | return | endif
+  let b:vimtex_syntax.subfile = 1
+
+  syntax match texInputFile /\\subfile\s*\%(\[.\{-}\]\)\=\s*{.\{-}}/
+        \ contains=texStatement,texInputCurlies,texInputFileOpt
+endfunction
+
+" }}}1
+
+endif