[visitor] Don't recurse on private or TTFont attributes

Lib/fontTools/misc/visitor.py

@@ -70,6 +70,8 @@ class Visitor(object):
         _visitors = self._visitorsFor(obj)
         defaultVisitor = _visitors.get("*", None)
         for key in keys:
+            if key[0] == "_":
+                continue
             value = getattr(obj, key)
             visitorFunc = _visitors.get(key, defaultVisitor)
             if visitorFunc is not None:

Lib/fontTools/ttLib/ttVisitor.py

@@ -5,6 +5,11 @@ from fontTools.ttLib import TTFont
 
 
 class TTVisitor(Visitor):
+    def visitAttr(self, obj, attr, value, *args, **kwargs):
+        if isinstance(value, TTFont):
+            return False
+        super().visitAttr(obj, attr, value, *args, **kwargs)
+
     def visit(self, obj, *args, **kwargs):
         if hasattr(obj, "ensureDecompiled"):
             obj.ensureDecompiled(recurse=False)