MAYA-125991 - Unable to switch variants when Session Layer is targeted

lib/mayaUsd/ufe/private/Utils.cpp

@@ -159,10 +159,20 @@ bool allowedInStrongerLayer(
 
     // If allowed, verify if the target layer is stronger than any existing layer with an opinion.
     auto stage = prim.GetStage();
-    auto rootLayer = stage->GetRootLayer();
     auto targetLayer = stage->GetEditTarget().GetLayer();
     auto topLayer = primStack.front()->GetLayer();
-    return getStrongerLayer(rootLayer, targetLayer, topLayer) == targetLayer;
+
+    // Session Layer is the strongest in the stage, so check its hierarchy first
+    auto strongerLayer = getStrongerLayer(stage->GetSessionLayer(), targetLayer, topLayer);
+    if (strongerLayer == targetLayer) {
+        return true;
+    } else if (strongerLayer == topLayer) {
+        return false;
+    }
+
+    // If none of the two layers was found in the Session Layer hierarchy,
+    // then proceed to the stage's general layer hierarchy
+    return getStrongerLayer(stage->GetRootLayer(), targetLayer, topLayer) == targetLayer;
 }
 
 } // namespace

test/lib/ufe/testContextOps.py

@@ -146,9 +146,9 @@ def testGetItems(self):
             if c.checked:
                 self.assertEqual(c.item, 'Ball_8')
 
-    def testSwitchVariantInWeakerLayer(self):
+    def testSwitchVariantInLayer(self):
         """
-        Test that switching variant in a weaker layer is restricted.
+        Test switching variant in layers: stronger, weaker, session.
         """
         contextItems = self.contextOps.getItems([])
 
@@ -200,7 +200,15 @@ def shadingVariantOnPrim():
         # Verify the variant has not switched.
         self.assertEqual(shadingVariant(), 'Cue')
         self.assertEqual(shadingVariantOnPrim(), 'Cue')
-
+
+        # Verify we can switch variant in Session Layer.
+        stage.SetEditTarget(stage.GetSessionLayer())
+        cmd = self.contextOps.doOpCmd(
+            ['Variant Sets', 'shadingVariant', 'Ball_8'])
+        self.assertIsNotNone(cmd)
+        ufeCmd.execute(cmd)
+        self.assertEqual(shadingVariant(), 'Ball_8')
+        self.assertEqual(shadingVariantOnPrim(), 'Ball_8')
 
     def testDoOp(self):
         # Change visibility, undo / redo.