From 0264754b4381c0e0d128b5135cbd7a72cb924fb0 Mon Sep 17 00:00:00 2001
From: Sylvester Kaczmarek
 <16242628+sylvesterkaczmarek@users.noreply.github.com>
Date: Sun, 11 Oct 2026 17:14:01 +0100
Subject: [PATCH] Skip missing MuJoCo struct fields during named indexing

---
 dm_control/mujoco/index.py      |  6 +++---
 dm_control/mujoco/index_test.py | 20 ++++++++++++++++++++
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/dm_control/mujoco/index.py b/dm_control/mujoco/index.py
index 76e534cc..f7dd7052 100644
--- a/dm_control/mujoco/index.py
+++ b/dm_control/mujoco/index.py
@@ -636,9 +636,9 @@ def struct_indexer(struct, struct_name, size_to_axis_indexer):
 
   for field_name in array_sizes:
 
-    # Skip over structured arrays and fields that have sizes but aren't numpy
-    # arrays, such as text fields and contacts (b/34805932).
-    attr = getattr(struct, field_name)
+    # Skip fields removed by newer MuJoCo versions even if older generated
+    # metadata still lists them, as well as non-array and structured fields.
+    attr = getattr(struct, field_name, None)
     if not isinstance(attr, np.ndarray) or attr.dtype.fields:
       continue
 
diff --git a/dm_control/mujoco/index_test.py b/dm_control/mujoco/index_test.py
index 3eaeae53..47f5d220 100644
--- a/dm_control/mujoco/index_test.py
+++ b/dm_control/mujoco/index_test.py
@@ -14,6 +14,7 @@
 # ============================================================================
 
 import collections
+from unittest import mock
 
 from absl.testing import absltest
 from absl.testing import parameterized
@@ -73,6 +74,25 @@ def setUp(self):
     self._data_indexers = index.struct_indexer(self._data, 'mjdata',
                                                self._size_to_axis_indexer)
 
+  def testStructIndexerSkipsRemovedDataFields(self):
+    # MuJoCo may remove a field that remains in generated array_sizes.
+    with mock.patch.dict(sizes.array_sizes['mjdata'],
+                         {'removed_data_field': ('nbody',)}):
+      named = index.struct_indexer(
+          self._data, 'mjdata', self._size_to_axis_indexer)
+    self.assertNotIn('removed_data_field', named._asdict())
+    self.assertIn('xpos', named._asdict())
+    np.testing.assert_array_equal(
+        named.xpos['cart'], self._data.xpos[1])
+
+  def testStructIndexerSkipsRemovedModelFields(self):
+    with mock.patch.dict(sizes.array_sizes['mjmodel'],
+                         {'removed_model_field': ('ngeom',)}):
+      named = index.struct_indexer(
+          self._model, 'mjmodel', self._size_to_axis_indexer)
+    self.assertNotIn('removed_model_field', named._asdict())
+    self.assertIn('geom_rgba', named._asdict())
+
   def assertIndexExpressionEqual(self, expected, actual):
     try:
       if isinstance(expected, tuple):