From e94f85fec422616f8b6c944d311d5c1a35945982 Mon Sep 17 00:00:00 2001
From: Patrick Totzke <patrick@totzke.uk>
Date: Sun, 25 Oct 2026 09:41:38 +0000
Subject: [PATCH] Route NestedTree's collapse calls through one helper

collapsible, is_collapsed, toggle_collapsed, collapse and expand each
looked up the tree managing the position and checked that it can
collapse; _on_subtree now does that once, replacing _get_subtree_for.
It walks down through NestedTrees nested directly in each other in a
loop, where the methods used to recurse once per level.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 tests/test_nested.py | 11 +++++++++++
 urwidtrees/nested.py | 39 +++++++++++++++++----------------------
 2 files changed, 28 insertions(+), 22 deletions(-)

diff --git a/tests/test_nested.py b/tests/test_nested.py
index 0dfed02..e995994 100644
--- a/tests/test_nested.py
+++ b/tests/test_nested.py
@@ -161,6 +161,17 @@ def test_collapse_all_reaches_hidden_subtrees(self):
         tree.expand_all()
         self.assertEqual(len(list(tree.positions())), 4)
 
+    def test_collapse_deeply_nested(self):
+        # no recursion per NestedTree wrapped directly in another
+        tree, x = self.inner, (0,)
+        for _ in range(1100):
+            tree, x = NestedTree(tree), (x,)
+        self.assertTrue(tree.collapsible(x))
+        tree.collapse(x)
+        self.assertTrue(self.inner.is_collapsed((0,)))
+        tree.expand(x)
+        self.assertFalse(tree.is_collapsed(x))
+
     def test_collapse_all_wide(self):
         outer = CollapsibleTree(SimpleTree([(Node('R'), [
             (Node(str(i)), [(Node('c'), None)]) for i in range(1500)])]))
diff --git a/urwidtrees/nested.py b/urwidtrees/nested.py
index fd71a87..a05845c 100644
--- a/urwidtrees/nested.py
+++ b/urwidtrees/nested.py
@@ -98,33 +98,30 @@ def decorate(self, pos, widget, is_first=True):
         return self._get_decorated_entry(pos, widget, is_first)
 
     # Collapse API
-    def _get_subtree_for(self, pos):
-        """returns Tree that manages pos[-1]"""
-        return self._trees(pos)[-1]
+    def _on_subtree(self, pos, method, default=None):
+        """
+        call `method` with pos[-1] on the tree that manages it, if that tree
+        can collapse; otherwise return `default`. A NestedTree nested
+        directly in another hands on to its own managing tree.
+        """
+        tree = self
+        while isinstance(tree, NestedTree):
+            tree, pos = tree._trees(pos)[-1], pos[-1]
+        if isinstance(tree, CollapseMixin):
+            return getattr(tree, method)(pos)
+        return default
 
     def collapsible(self, pos):
-        res = False
-        subtree = self._get_subtree_for(pos)
-        if isinstance(subtree, (CollapseMixin, NestedTree)):
-            res = subtree.collapsible(pos[-1])
-        return res
+        return self._on_subtree(pos, 'collapsible', False)
 
     def is_collapsed(self, pos):
-        res = False
-        subtree = self._get_subtree_for(pos)
-        if isinstance(subtree, (CollapseMixin, NestedTree)):
-            res = subtree.is_collapsed(pos[-1])
-        return res
+        return self._on_subtree(pos, 'is_collapsed', False)
 
     def toggle_collapsed(self, pos):
-        subtree = self._get_subtree_for(pos)
-        if isinstance(subtree, (CollapseMixin, NestedTree)):
-            subtree.toggle_collapsed(pos[-1])
+        self._on_subtree(pos, 'toggle_collapsed')
 
     def collapse(self, pos):
-        subtree = self._get_subtree_for(pos)
-        if isinstance(subtree, (CollapseMixin, NestedTree)):
-            subtree.collapse(pos[-1])
+        self._on_subtree(pos, 'collapse')
 
     def collapse_all(self):
         for tree in self._expand_all():
@@ -132,9 +129,7 @@ def collapse_all(self):
                 tree.collapse_all()
 
     def expand(self, pos):
-        subtree = self._get_subtree_for(pos)
-        if isinstance(subtree, (CollapseMixin, NestedTree)):
-            subtree.expand(pos[-1])
+        self._on_subtree(pos, 'expand')
 
     def expand_all(self):
         self._expand_all()