HYDRA-1160 : Fix crash when traversing prototype prims without prototype roots for highlighting

lib/flowViewport/sceneIndex/fvpWireframeSelectionHighlightSceneIndex.cpp

@@ -104,9 +104,13 @@ SdfPathVector _GetInstancingRelatedPaths(const HdSceneIndexPrim& prim, Fvp::Sele
             instancingRelatedPaths.push_back(instancerPath);
         }
 
-        auto protoRootPaths = instancedBy.GetPrototypeRoots()->GetTypedValue(0);
-        for (const auto& protoRootPath : protoRootPaths) {
-            instancingRelatedPaths.push_back(protoRootPath);
+        // Having a prototype root is not a hard requirement (a single prim being instanced
+        // does not need to specify itself as its own prototype root).
+        if (instancedBy.GetPrototypeRoots()) {
+            auto protoRootPaths = instancedBy.GetPrototypeRoots()->GetTypedValue(0);
+            for (const auto& protoRootPath : protoRootPaths) {
+                instancingRelatedPaths.push_back(protoRootPath);
+            }
         }
     }
 

test/lib/mayaUsd/render/mayaToHydra/cpp/testDataProducerExample.py

@@ -58,6 +58,9 @@ def cube000PathString(self):
     def cube222PathString(self):
         return '|transform1|' + self._locator + ',/cube_2_2_2'
 
+    def cubePrototypePathString(self):
+        return '|transform1|' + self._locator + ',/cube_'
+
     def test_Pick(self):
         # Pick an exterior cube to ensure we don't pick a hidden one.
         cmds.mayaHydraCppTest(self.cube222PathString(), f='TestUsdPicking.pick')
@@ -132,5 +135,26 @@ def assertTranslationAlmostEqual(expected):
         cmds.redo()
         assertTranslationAlmostEqual([3, 4, 5])
 
+    def test_SelectPrototype(self):
+        # Enable instancing
+        cmds.setAttr(self._locator + '.cubesUseInstancing', True)
+
+        # Clear selection
+        sn = ufe.GlobalSelection.get()
+        sn.clear()
+
+        # Empty Maya selection, therefore no fully selected path in the scene
+        # index.
+        cmds.mayaHydraCppTest(f='TestSelection.fullySelectedPaths')
+
+        # Add cube to selection
+        item = ufe.Hierarchy.createItem(ufe.PathString.path(self.cubePrototypePathString()))
+        sn.append(item)
+
+        # Item added to the Maya selection, it should be fully selected in the
+        # scene index.
+        cmds.mayaHydraCppTest(
+            self.cubePrototypePathString(), f='TestSelection.fullySelectedPaths')
+
 if __name__ == '__main__':
     fixturesUtils.runTests(globals())