Restrict mjc resolver fix to physics import paths

Author: AntoineRichard

source/isaaclab/changelog.d/antoiner-mjc-frictionloss.skip

@@ -432,11 +432,7 @@ def _get_names_from_newton_usd_builder(
 
     try:
         from newton import JointType, ModelBuilder, solvers  # noqa: PLC0415
-        from newton._src.usd.schemas import (  # noqa: PLC0415
-            SchemaResolverMjc,
-            SchemaResolverNewton,
-            SchemaResolverPhysx,
-        )
+        from newton._src.usd.schemas import SchemaResolverNewton, SchemaResolverPhysx  # noqa: PLC0415
         from newton.selection import ArticulationView  # noqa: PLC0415
 
         from pxr import UsdGeom, UsdPhysics  # noqa: PLC0415
@@ -482,7 +478,7 @@ def has_articulation_root_api(prim) -> bool:
         root_path=source_asset_path,
         load_visual_shapes=False,
         skip_mesh_approximation=True,
-        schema_resolvers=[SchemaResolverNewton(), SchemaResolverPhysx(), SchemaResolverMjc()],
+        schema_resolvers=[SchemaResolverNewton(), SchemaResolverPhysx()],
         joint_ordering=joint_ordering,
         bodies_follow_joint_ordering=bodies_follow_joint_ordering,
     )

source/isaaclab/isaaclab/assets/articulation/ordering_resolvers.py

@@ -768,7 +768,6 @@ def __init__(self, model, pattern, **kwargs):
     schemas_mod = types.ModuleType("newton._src.usd.schemas")
     schemas_mod.SchemaResolverNewton = lambda: "newton_schema"
     schemas_mod.SchemaResolverPhysx = lambda: "physx_schema"
-    schemas_mod.SchemaResolverMjc = lambda: "mjc_schema"
     stage_mod = types.ModuleType("isaaclab.sim.utils.stage")
     stage_mod.get_current_stage = lambda: stage
     monkeypatch.setitem(sys.modules, "newton", newton_mod)

source/isaaclab/test/assets/test_articulation_ordering.py

@@ -10,7 +10,7 @@
 
 import torch
 from newton import ModelBuilder
-from newton._src.usd.schemas import SchemaResolverMjc, SchemaResolverNewton, SchemaResolverPhysx
+from newton._src.usd.schemas import SchemaResolverNewton, SchemaResolverPhysx
 
 from pxr import Usd
 
@@ -95,7 +95,7 @@ def build_visualization_builder_from_stage_envs(
         A tuple of the populated :class:`~newton.ModelBuilder` and shadow-deformable
         metadata ``(shadow_entities, registry_groups)``.
     """
-    schema_resolvers = [SchemaResolverNewton(), SchemaResolverPhysx(), SchemaResolverMjc()]
+    schema_resolvers = [SchemaResolverNewton(), SchemaResolverPhysx()]
     builder = ModelBuilder(up_axis=up_axis)
     # Discover once and reuse via ``entries=`` below (ignore paths + shadow add).
     deformable_entries = discover_deformables_on_stage(stage)

source/isaaclab_newton/isaaclab_newton/physics/visualization_builder.py

@@ -1592,3 +1592,50 @@ def test_hard_reset_then_step_runs(use_cuda_graph):
         # A hard device sync surfaces any deferred illegal access as an exception.
         sim.step(render=False)
         wp.synchronize_device("cuda:0")
+
+
+# ---------------------------------------------------------------------------
+# Regression: USD-authored ``mjc:*`` joint attributes must reach the Newton
+# model through the manager import path (https://github.com/isaac-sim/IsaacLab/issues/6829).
+# ---------------------------------------------------------------------------
+
+
+def _author_revolute_with_frictionloss(stage, frictionloss: float) -> None:
+    """Author a two-body articulation whose revolute joint carries ``mjc:frictionloss``."""
+    from pxr import Sdf, UsdGeom, UsdPhysics
+
+    world = UsdGeom.Xform.Define(stage, "/World/robot")
+    UsdPhysics.ArticulationRootAPI.Apply(world.GetPrim())
+    for name in ("parent", "child"):
+        body = UsdGeom.Cube.Define(stage, f"/World/robot/{name}")
+        UsdPhysics.RigidBodyAPI.Apply(body.GetPrim())
+        UsdPhysics.MassAPI.Apply(body.GetPrim()).CreateMassAttr(1.0)
+    fixed = UsdPhysics.FixedJoint.Define(stage, "/World/robot/fix")
+    fixed.CreateBody1Rel().SetTargets(["/World/robot/parent"])
+    joint = UsdPhysics.RevoluteJoint.Define(stage, "/World/robot/rev")
+    joint.CreateBody0Rel().SetTargets(["/World/robot/parent"])
+    joint.CreateBody1Rel().SetTargets(["/World/robot/child"])
+    joint.CreateAxisAttr("Z")
+    joint.GetPrim().CreateAttribute("mjc:frictionloss", Sdf.ValueTypeNames.Float, custom=True).Set(frictionloss)
+
+
+def test_usd_mjc_frictionloss_reaches_newton_model():
+    """A USD joint authored with ``mjc:frictionloss`` yields a matching ``joint_friction``."""
+    import isaaclab.sim as sim_utils
+
+    sim_cfg = SimulationCfg(
+        dt=0.005,
+        device="cuda:0",
+        physics=NewtonCfg(solver_cfg=MJWarpSolverCfg(), num_substeps=1, use_cuda_graph=False),
+    )
+    with build_simulation_context(sim_cfg=sim_cfg):
+        stage = sim_utils.get_current_stage()
+        _author_revolute_with_frictionloss(stage, frictionloss=0.11)
+
+        NewtonManager.instantiate_builder_from_stage()
+        model = NewtonManager._builder.finalize()
+
+        friction = model.joint_friction.numpy()
+        assert friction.max() == pytest.approx(0.11), (
+            f"mjc:frictionloss was dropped by the USD import (joint_friction={friction})"
+        )