Store asset keys relative to the MJCF. This CL fixes cases when loading a spec with "from_zip" that fails on zipped folders that contain a root directory.

PiperOrigin-RevId: 825484553
Change-Id: I79c6f542edbd3ffd167d0b5cecc704c32c8d6824

python/mujoco/specs_test.py

@@ -1615,5 +1615,25 @@ class SpecsTest(absltest.TestCase):
     self.assertEqual(wrap_joint2.type, mujoco.mjtWrap.mjWRAP_JOINT)
     self.assertEqual(wrap_joint2.coef, 2.0)
 
+  def test_from_zip(self):
+    """Tests that the assets are correctly parsed from a zip file."""
+    model_path_root = (
+        epath.resource_path("mujoco") / "testdata" / "MJCF_Root.zip"
+    )
+    model_path_no_root = (
+        epath.resource_path("mujoco") / "testdata" / "MJCF_NoRoot.zip"
+    )
+    filenames = [model_path_root.as_posix(), model_path_no_root.as_posix()]
+
+    for filename in filenames:
+      with self.subTest(filename):
+        spec = mujoco.MjSpec.from_zip(filename)
+        spec.compile()
+        assets = spec.assets
+        xml_string = spec.to_xml()
+        string_spec = mujoco.MjSpec.from_string(xml_string, assets=assets)
+        string_spec.compile()
+        self.assertEqual(spec.to_xml(), string_spec.to_xml())
+
 if __name__ == '__main__':
   absltest.main()