mayaUSDImport crashes Maya when a mesh has authored normals and a dualQuaternion skinningMethod

[ldecampos]

Summary

mayaUSDImport hard-crashes Maya when the imported layer carries authored normals together with a primvars:skel:skinningMethod = dualQuaternion binding. Both halves are required: a linear skin with normals imports fine, and a dual-quaternion skin whose normals were removed imports fine.

The crash is easy to miss because mayaUSDExport only authors normals when the mesh is written as polygonal (defaultMeshScheme="none"); with the default catmullClark scheme USD ignores normals, none are authored, and the same rig round-trips cleanly. Rigging exports are polygonal, so this is on the common path for character work.

The script below was run on Maya 2025.3.2 (mayaUsd 0.32.0 / USD 23.11), Maya 2026 (0.34.0 / USD 24.11) and Maya 2027 (0.35.0 / USD 25.11) on macOS 26.5 (Apple Silicon): all three terminate. It happens in a clean session, with no other plug-in or Python module involved.

Steps to reproduce

Run in the Script Editor of a freshly opened Maya (it crashes on the last line):

from maya import cmds
import tempfile

cmds.loadPlugin("mayaUsdPlugin", quiet=True)
cmds.file(new=True, force=True)

names = ("root", "spine", "chest", "shoulder", "elbow", "wrist")
grp = cmds.group(empty=True, name="rig")
cmds.select(clear=True)
joints = [cmds.joint(name=n, position=(0.0, float(i), 0.0))
          for i, n in enumerate(names)]
cmds.parent(joints[0], grp)

mesh = cmds.polySphere(name="body", subdivisionsX=8, subdivisionsY=6)[0]
cmds.parent(mesh, grp)
skin = cmds.skinCluster(*joints, mesh, toSelectedBones=True)[0]
cmds.setAttr(skin + ".skinningMethod", 1)  # dual quaternion

path = tempfile.mkdtemp() + "/dq.usda"
cmds.mayaUSDExport(file=path, exportSkels="auto", exportSkin="auto",
                   defaultMeshScheme="none")  # polygonal: normals ARE authored

cmds.file(new=True, force=True)
cmds.mayaUSDImport(file=path)  # <-- Maya crashes here

Expected: the mesh is imported and bound to a skinCluster with skinningMethod = 1.
Actual: Maya terminates. This warning is always printed immediately before the crash:

// Warning: Cycle on 'skinCluster_body.outputGeometry[0]' may not evaluate as expected.

Isolation

Editing the very same exported layer with pxr before importing it shows that both ingredients are necessary — either edit makes the import succeed:

Layer content	Import result
dualQuaternion + authored normals (as exported)	crash
dualQuaternion, normals property removed	OK — skinningMethod = 1 restored
normals kept, skinningMethod set to classicLinear	OK
exported with the default catmullClark scheme (no normals authored)	OK — skinningMethod = 1 restored

Removing the subdivisionScheme difference alone is not enough: setting subdivisionScheme = "catmullClark" on a layer that still carries authored normals still crashes. The mesh scheme only matters because it decides whether normals get authored.

Stack

From the macOS microstackshot report captured during the crash (/Library/Logs/DiagnosticReports/Maya_*.cpu_resource.diag), the import triggers a DG evaluation of the still half-connected network, and the skinCluster dies in the dual-quaternion normal path:

mayaUSDImport
  MFnMesh::MFnMesh(MObject const&, MStatus*)
  MFnBase::setObject(MObject const&)
  MFnMesh::objectChanged(...)
  TmeshShape::inMeshData() const
  TdataBlockDG::value(Tattribute const&)
  Tplug::evaluateValue(...)
  TdependNode::dbEvaluate(TmsgEval&)
  TDNskinCluster::computePlug(Tplug const&, TdataBlock&)
  TdnGeometryFilter::computePlug(Tplug const&, TdataBlock&)
  TDNskinCluster::deformGeom(...)
  TDNskinCluster::deformNormalsQuat(T4dDblMatrix const&, T3dFltVectorArray&, float, maya_zamboni::DeformCache*)
  libtbb.12.14.dylib
  _sigtramp

deformNormalsQuat runs only for dual-quaternion skinning, which matches the observed conjunction: linear skins never reach it, and with no authored normals there is nothing for it to deform during the import.

Workaround

Strip the normals property from the skinned meshes of the exported layer before importing. Normals of a skinned mesh are derived data (Maya recomputes them from the deformed geometry), so nothing is lost:

from pxr import Usd

stage = Usd.Stage.Open(path)
for prim in stage.Traverse():
    prim.RemoveProperty("normals")
stage.Save()