Select prim without data source must not crash.

lib/flowViewport/sceneIndex/fvpSelectionSceneIndex.cpp

@@ -76,7 +76,7 @@ class _PrimSource : public HdContainerDataSource
 
     TfTokenVector GetNames() override
     {
-        TfTokenVector names = _inputSource->GetNames();
+        TfTokenVector names = _inputSource ? _inputSource->GetNames() : TfTokenVector();
         if (_selection->IsFullySelected(_primPath)) {
             names.push_back(HdSelectionsSchemaTokens->selections);
         }
@@ -89,7 +89,7 @@ class _PrimSource : public HdContainerDataSource
             return _selection->GetVectorDataSource(_primPath);
         }
 
-        return _inputSource->Get(name);
+        return _inputSource ? _inputSource->Get(name) : nullptr;
     }
 
 private:
@@ -132,7 +132,12 @@ SelectionSceneIndex::GetPrim(const SdfPath &primPath) const
         .Msg("SelectionSceneIndex::GetPrim() called.\n");
 
     HdSceneIndexPrim result = GetInputSceneIndex()->GetPrim(primPath);
-    if (!result.dataSource) {
+    // An empty data source can be taken to mean an invalid prim, but it can
+    // also be an ancestor in a path to an actual prim (see
+    // https://forum.aousd.org/t/representation-of-invalid-hdsceneindexprim/833/2
+    // ).  Such an ancestor prim can be selected, even if typeless, so add
+    // a selection data source in such a case.
+    if (!result.dataSource && !_selection->IsFullySelected(primPath)) {
         return result;
     }
 

test/lib/mayaUsd/render/mayaToHydra/CMakeLists.txt

@@ -15,6 +15,7 @@ set(INTERACTIVE_TEST_SCRIPT_FILES
     testNamespaces.py
     testVisibility.py
     testRendererSwitching.py
+    testSelectPrimWithoutDataSource.py
     testStageAddPrim.py
     testTransforms.py
     testRefinement.py

test/lib/mayaUsd/render/mayaToHydra/testSelectPrimWithoutDataSource.py

@@ -0,0 +1,58 @@
+# Copyright 2024 Autodesk
+#
+# 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.
+#
+import maya.cmds as cmds
+
+import fixturesUtils
+import mtohUtils
+import testUtils
+import usdUtils
+
+class TestSelectPrimWithoutDataSource(mtohUtils.MayaHydraBaseTestCase):
+    # MayaHydraBaseTestCase.setUpClass requirement.
+    _file = __file__
+
+    def test_selectPrimWithoutDataSource(self):
+
+        # Importing mayaUsd or mayaUsd.lib at module scope produces an "unbound
+        # local" error on use, so import in local scope.  May be tied to 
+        # point at which mayaUsd plugin gets loaded into Maya.
+        import mayaUsd.lib
+
+        # Prims without a data source are sometimes used to flag illegal prim
+        # return values, but such prims can also be legitimately used as parent
+        # prims for children prims that do have data sources.  As such a prim
+        # without a data source must be selectable.
+
+        # Read in a scene that creates a legal Hydra parent prim without a data
+        # source.
+        usdScenePath = testUtils.getTestScene('testSelectPrimWithoutDataSource', 'root.usda')
+
+        self.proxyShapePathStr = usdUtils.createStageFromFile(usdScenePath)
+
+        stage = mayaUsd.lib.GetPrim(self.proxyShapePathStr).GetStage()
+
+        self.assertIsNotNone(stage)
+
+        # Initially select the proxy shape.
+        cmds.select('|root|rootShape')
+        cmds.refresh()
+
+        # Switch selection to a USD prim that generates a Hydra prim without
+        # a data source, but with children.  This must not crash.
+        cmds.select('|root|rootShape,/root/refAssetB')
+        cmds.refresh()
+
+if __name__ == '__main__':
+    fixturesUtils.runTests(globals())

test/testSamples/testSelectPrimWithoutDataSource/cube.usda

@@ -0,0 +1,25 @@
+#usda 1.0
+(
+    defaultPrim = "cube"
+)
+
+def Xform "cube" (
+    prepend apiSchemas = ["GeomModelAPI"]
+    kind = "component"
+)
+{
+    uniform bool model:applyDrawMode = 1
+    asset model:cardTextureXNeg = @./red20x20.png@
+    asset model:cardTextureXPos = @./red20x20.png@
+    asset model:cardTextureYNeg = @./red20x20.png@
+    asset model:cardTextureYPos = @./red20x20.png@
+    asset model:cardTextureZNeg = @./red20x20.png@
+    asset model:cardTextureZPos = @./red20x20.png@
+
+    def Mesh "cubeMesh"
+    {
+        int[] faceVertexCounts = [4, 4, 4, 4, 4, 4]
+        int[] faceVertexIndices = [0, 1, 3, 2, 2, 3, 5, 4, 4, 5, 7, 6, 6, 7, 1, 0, 1, 7, 5, 3, 6, 0, 2, 4]
+        point3f[] points = [(-0.5, -0.5, 0.5), (0.5, -0.5, 0.5), (-0.5, 0.5, 0.5), (0.5, 0.5, 0.5), (-0.5, 0.5, -0.5), (0.5, 0.5, -0.5), (-0.5, -0.5, -0.5), (0.5, -0.5, -0.5)]
+    }
+}

test/testSamples/testSelectPrimWithoutDataSource/root.usda

@@ -0,0 +1,29 @@
+#usda 1.0
+(
+    defaultPrim = "root"
+)
+
+def Xform "root" (
+    kind = "assembly"
+)
+{
+    def Xform "refAssetA" (
+        references = @./cube.usda@
+        kind = "group"
+    )
+    {
+        double3 xformOp:rotateXYZ = (-90, 0, 0)
+        double3 xformOp:translate = (-5, 0, 0)
+        uniform token[] xformOpOrder = ["xformOp:rotateXYZ", "xformOp:translate"]
+    }
+    def Xform "refAssetB" (
+        references = @./cube.usda@
+        kind = "group"
+    )
+    {
+        uniform token model:drawMode = "cards"
+        double3 xformOp:rotateXYZ = (-90, 0, 0)
+        double3 xformOp:translate = (5, 0, 0)
+        uniform token[] xformOpOrder = ["xformOp:rotateXYZ", "xformOp:translate"]
+    }
+}