1 files changed, 32 insertions, 0 deletions
diff --git a/Lib/fontTools/ttLib/ttVisitor.py b/Lib/fontTools/ttLib/ttVisitor.py
new file mode 100644
index 00000000..54db61b1
--- /dev/null
+++ b/Lib/fontTools/ttLib/ttVisitor.py
@@ -0,0 +1,32 @@
+"""Specialization of fontTools.misc.visitor to work with TTFont."""
+
+from fontTools.misc.visitor import Visitor
+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)
+        super().visit(obj, *args, **kwargs)
+
+
+@TTVisitor.register(TTFont)
+def visit(visitor, font, *args, **kwargs):
+    # Some objects have links back to TTFont; even though we
+    # have a check in visitAttr to stop them from recursing
+    # onto TTFont, sometimes they still do, for example when
+    # someone overrides visitAttr.
+    if hasattr(visitor, "font"):
+        return False
+
+    visitor.font = font
+    for tag in font.keys():
+        visitor.visit(font[tag], *args, **kwargs)
+    del visitor.font
+    return False