Use upstreadm mdx ftdetect

build

@@ -63,7 +63,7 @@ extract() {
 
     output "${subdirs##, })"$'\n'
 
-    if (echo "julia coffee-script elixir fish git plantuml scala swift jinja mdx" | grep -qF "$name"); then
+    if (echo "julia coffee-script elixir fish git plantuml scala swift jinja" | grep -qF "$name"); then
       echo "Skipping ftdetect installation of $name" >&2
       continue
     fi

ftdetect/polyglot.vim

@@ -711,6 +711,19 @@ au BufRead,BufNewFile *.{md,mdown,mkd,mkdn,markdown,mdwn}.{des3,des,bf,bfa,aes,i
   augroup end
 endif
 
+if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'mdx') == -1
+  augroup filetypedetect
+  " mdx, from mdx.vim in jxnblk/vim-mdx-js
+" Vim ftdetect file
+"
+" Language: MDX
+" Maintainer: Brent Jackson <jxnblk@gmail.com>
+"
+
+autocmd BufNewFile,BufRead *.mdx set filetype=markdown.mdx
+  augroup end
+endif
+
 if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'meson') == -1
   augroup filetypedetect
   " meson, from meson.vim in mesonbuild/meson:_ALL:/data/syntax-highlighting/vim/