Fix AttributeError in egl.GLContext.__del__ on partial construction

python/mujoco/egl/__init__.py

@@ -83,6 +83,7 @@ class GLContext:
   """An EGL context for headless accelerated OpenGL rendering on GPU devices."""
 
   def __init__(self, max_width, max_height):
+    self._context = None
     del max_width, max_height  # unused
     num_configs = ctypes.c_long()
     config_size = 1

python/mujoco/egl_gl_context_test.py

@@ -0,0 +1,89 @@
+# Copyright 2026 DeepMind Technologies Limited
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Tests for the EGL GLContext's __del__ safety on partial construction."""
+
+import gc
+import sys
+from unittest import mock
+
+from absl.testing import absltest
+
+try:
+  from mujoco import egl as egl_module
+except ImportError:
+  # The EGL backend can only be imported on systems where libEGL/libOpenGL
+  # are present (see mujoco/egl/egl_ext.py). That is an environment
+  # precondition orthogonal to the bug under test here, so we skip rather
+  # than fail when it is unavailable (e.g. this is the case for the CI
+  # matrix, which runs with MUJOCO_GL=disable).
+  egl_module = None
+
+
+@absltest.skipIf(
+    egl_module is None,
+    'The EGL backend could not be imported in this environment.',
+)
+class EglGlContextTest(absltest.TestCase):
+  """Regression test for GLContext.__del__ on a partially-constructed instance.
+
+  If `GLContext.__init__` raises before `self._context` is assigned -- e.g.
+  because the EGL driver does not support the PLATFORM_DEVICE extension and
+  `create_initialized_egl_device_display()` returns `EGL_NO_DISPLAY`, so
+  `__init__` raises `ImportError` -- garbage collection later runs
+  `__del__` -> `free()`, which used to unconditionally read `self._context`
+  and raise `AttributeError: 'GLContext' object has no attribute
+  '_context'`. That AttributeError masked the real, actionable ImportError
+  raised from `__init__`. See issue #991, and the same bug class fixed for
+  `Renderer` in #3225 (issue #3213).
+
+  We can't rely on the test host's EGL driver actually lacking
+  PLATFORM_DEVICE support, so we force that branch deterministically by
+  patching `create_initialized_egl_device_display` to return
+  `EGL.EGL_NO_DISPLAY`, exactly as it would on such a host. This drives a
+  real `GLContext.__init__` call through its real failure path, rather than
+  bypassing `__init__` altogether.
+  """
+
+  def test_del_safe_when_init_fails_without_platform_device_support(self):
+    unraisable = []
+    old_hook = sys.unraisablehook
+    sys.unraisablehook = lambda args: unraisable.append(args)
+    try:
+      with mock.patch.object(egl_module, 'EGL_DISPLAY', None), \
+          mock.patch.object(
+              egl_module,
+              'create_initialized_egl_device_display',
+              return_value=egl_module.EGL.EGL_NO_DISPLAY,
+          ):
+        # __init__ must still raise ImportError -- that's the real,
+        # actionable error this bug used to mask.
+        with self.assertRaises(ImportError):
+          egl_module.GLContext(640, 480)
+        gc.collect()
+    finally:
+      sys.unraisablehook = old_hook
+
+    self.assertEqual(
+        [u.exc_type.__name__ for u in unraisable],
+        [],
+        msg=(
+            'GLContext.__del__ raised on a partially-constructed instance; '
+            'see #991.'
+        ),
+    )
+
+
+if __name__ == '__main__':
+  absltest.main()