Ensure snippets are loaded for current filetype

Force a refresh also for the FileType autocommand.

autoload/UltiSnips.vim

@@ -183,6 +183,10 @@ function! UltiSnips#TrackChange() abort
     py3 UltiSnips_Manager._track_change()
 endfunction
 
+function! UltiSnips#CheckFiletype() abort
+    py3 UltiSnips_Manager._check_filetype(vim.eval('&ft'))
+endfunction
+
 function! UltiSnips#RefreshSnippets() abort
     py3 UltiSnips_Manager._refresh_snippets()
 endfunction

plugin/UltiSnips.vim

@@ -41,6 +41,7 @@ augroup UltiSnips_AutoTrigger
     if exists('##TextChangedP')
         au TextChangedP * call UltiSnips#TrackChange()
     endif
+    au FileType * call UltiSnips#CheckFiletype()
 augroup END
 
 call UltiSnips#map_keys#MapKeys()

pythonx/UltiSnips/snippet_manager.py

@@ -130,6 +130,7 @@ def __init__(self, expand_trigger, forward_trigger, backward_trigger):
         self._visual_content = VisualContentPreserver()
 
         self._snippet_sources = []
+        self._filetypes = []
 
         self._snip_expanded_in_action = False
         self._inside_action = False
@@ -975,6 +976,15 @@ def _refresh_snippets(self):
             source.refresh()
 
 
+    @err_to_scratch_buffer.wrap
+    def _check_filetype(self, ft):
+        """Ensure snippets are loaded for the current filetype."""
+        if ft not in self._filetypes:
+            self._filetypes.append(ft)
+            for _, source in self._snippet_sources:
+                source.refresh()
+
+
 UltiSnips_Manager = SnippetManager(  # pylint:disable=invalid-name
     vim.eval("g:UltiSnipsExpandTrigger"),
     vim.eval("g:UltiSnipsJumpForwardTrigger"),