Fix custom text properties for semantic highlighting

We were supposed to allow users to set highlight groups for any token
types that we don't understand, as servers can basically return anything
they like. This didn't work and we just always complained about it.

Now we trap the "text property type doesn't exist" error and warn then.
This allows users to specify the missing ones to stfu the error. Also
improved the message to point to the help.

Author: puremourning

python/ycm/semantic_highlighting.py

@@ -22,6 +22,8 @@
 from ycm import text_properties as tp
 from ycm import scrolling_range as sr
 
+import vim
+
 
 HIGHLIGHT_GROUP = {
   'namespace': 'Type',
@@ -107,16 +109,21 @@ def _Draw( self ):
     self._prop_id = NextPropID()
 
     for token in tokens:
-      if token[ 'type' ] not in HIGHLIGHT_GROUP:
-        if token[ 'type' ] not in REPORTED_MISSING_TYPES:
-          REPORTED_MISSING_TYPES.add( token[ 'type' ] )
-          vimsupport.PostVimMessage(
-            f"Missing property type for { token[ 'type' ] }" )
-        continue
       prop_type = f"YCM_HL_{ token[ 'type' ] }"
-
       rng = token[ 'range' ]
       self.GrowRangeIfNeeded( rng )
-      tp.AddTextProperty( self._bufnr, self._prop_id, prop_type, rng )
+
+      try:
+        tp.AddTextProperty( self._bufnr, self._prop_id, prop_type, rng )
+      except vim.error as e:
+        if 'E971:' in str( e ): # Text property doesn't exist
+          if token[ 'type' ] not in REPORTED_MISSING_TYPES:
+            REPORTED_MISSING_TYPES.add( token[ 'type' ] )
+            vimsupport.PostVimMessage(
+              f"Token type { token[ 'type' ] } not supported. "
+              f"Define property type { prop_type }. "
+              f"See :help youcompleteme-customising-highlight-groups" )
+        else:
+          raise e
 
     tp.ClearTextProperties( self._bufnr, prop_id = prev_prop_id )