From 8fe672c6a274c307188f633507ee773cad7fcdef Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Sun, 31 Jul 2022 12:27:09 -0600
Subject: [PATCH] Add misc.visitor.py

Fixes https://github.com/fonttools/fonttools/issues/1959
---
 Lib/fontTools/misc/visitor.py | 82 +++++++++++++++++++++++++++++++++++
 Tests/misc/visitor_test.py    | 19 ++++++++
 2 files changed, 101 insertions(+)
 create mode 100644 Lib/fontTools/misc/visitor.py
 create mode 100644 Tests/misc/visitor_test.py

diff --git a/Lib/fontTools/misc/visitor.py b/Lib/fontTools/misc/visitor.py
new file mode 100644
index 000000000..4ee464abd
--- /dev/null
+++ b/Lib/fontTools/misc/visitor.py
@@ -0,0 +1,82 @@
+
+class Visitor(object):
+
+	defaultStop = False
+
+	@classmethod
+	def register(celf, clazzes, attrs=(None,)):
+		assert celf != Visitor, 'Subclass Visitor instead.'
+		if '_visitors' not in celf.__dict__:
+			celf._visitors = {}
+		if type(clazzes) != tuple:
+			clazzes = (clazzes,)
+		if type(attrs) == str:
+			attrs = (attrs,)
+		def wrapper(method):
+			assert method.__name__ == 'visit'
+			done = []
+			for clazz in clazzes:
+				if clazz in done: continue # Support multiple names of a clazz
+				done.append(clazz)
+				_visitors = celf._visitors.setdefault(clazz, {})
+				for attr in attrs:
+					assert attr not in _visitors, \
+						"Oops, class '%s' has visitor function for '%s' defined already." % (clazz.__name__, attr)
+					_visitors[attr] = method
+			return None
+		return wrapper
+
+	@classmethod
+	def _visitorsFor(celf, thing, _default={}):
+		typ = type(thing)
+
+		for celf in celf.mro():
+
+			_visitors = getattr(celf, '_visitors', None)
+			if _visitors is None:
+				break;
+
+			m = celf._visitors.get(typ, None)
+			if m is not None:
+				return m
+
+		return _default
+
+	def visitObject(self, obj, *args, **kwargs):
+		keys = sorted(vars(obj).keys())
+		_visitors = self._visitorsFor(obj)
+		defaultVisitor = _visitors.get('*', None)
+		for key in keys:
+			value = getattr(obj, key)
+			visitorFunc = _visitors.get(key, defaultVisitor)
+			if visitorFunc is not None:
+				ret = visitorFunc(self, obj, key, value, *args, **kwargs)
+				if ret == False or (ret is None and self.defaultStop):
+				  continue
+			self.visitAttr(obj, key, value, *args, **kwargs)
+
+	def visitAttr(self, obj, attr, value, *args, **kwargs):
+		self.visit(value, *args, **kwargs)
+
+	def visitList(self, obj, *args, **kwargs):
+		for value in obj:
+			self.visit(value, *args, **kwargs)
+
+	def visit(self, obj, *args, **kwargs):
+		visitorFunc = self._visitorsFor(obj).get(None, None)
+		if visitorFunc is not None:
+			ret = visitorFunc(self, obj, *args, **kwargs)
+			if ret == False or (ret is None and self.defaultStop):
+			  return
+		if hasattr(obj, '__dict__'):
+			self.visitObject(obj, *args, **kwargs)
+		elif isinstance(obj, list):
+			self.visitList(obj, *args, **kwargs)
+
+
+class OTVisitor(Visitor):
+
+	def visit(self, obj, *args, **kwargs):
+		if hasattr(obj, "ensureDecompiled"):
+			obj.ensureDecompiled(recurse=False)
+		super().visit(obj, *args, **kwargs)
diff --git a/Tests/misc/visitor_test.py b/Tests/misc/visitor_test.py
new file mode 100644
index 000000000..596f6ec28
--- /dev/null
+++ b/Tests/misc/visitor_test.py
@@ -0,0 +1,19 @@
+
+class TestVisitor(OTVisitor):
+    pass
+
+import fontTools.ttLib.tables.otTables as otTables
+
+@TestVisitor.register(otTables.Lookup)
+def visit(visitor, obj):
+    print(obj)
+    return False
+
+from fontTools.ttLib import TTFont
+import sys
+
+font = TTFont(sys.argv[1])
+gsub = font['GSUB']
+
+visitor = TestVisitor()
+visitor.visit(gsub)