EMSUSD-2659 - Fixes layer auto switching when the current target isn't locked.

lib/mayaUsd/commands/layerEditorCommand.cpp

@@ -142,6 +142,10 @@ void BaseCmd::updateEditTarget(const PXR_NS::UsdStageWeakPtr stage)
     if (stage->GetEditTarget().GetLayer() == stage->GetSessionLayer())
         return;
 
+    // If the currently targeted layer isn't locked, we don't need to change it.
+    if (!MayaUsd::isLayerLocked(stage->GetEditTarget().GetLayer()))
+        return;
+
     // If there are no target-able layers, we set the target to session layer.
     std::string errMsg;
     if (!UsdUfe::isAnyLayerModifiable(stage, &errMsg)) {

test/lib/testMayaUsdLayerEditorCommands.py

@@ -879,13 +879,16 @@ def _verifyStageAfterRefreshSystemLock(
             if expectedLayerModifiable:
                 # The initial target should be preserved in this case.
                 expectedTargetLayer = rootLayer
+                self.assertEqual(stage.GetEditTarget().GetLayer(), expectedTargetLayer)
             else:
-                # Edit target should have been forced to session layer.
-                expectedTargetLayer = stage.GetSessionLayer()
-
-            self.assertEqual(stage.GetEditTarget().GetLayer(),
-                             expectedTargetLayer)
-
+                # Edit target should have been forced to session layer 
+                # or unchanged if the current targeted layer is modifiable.
+                if mayaUsd.lib.isLayerLocked(stage.GetEditTarget().GetLayer()):
+                    expectedTargetLayer = stage.GetSessionLayer()
+                    self.assertEqual(stage.GetEditTarget().GetLayer(), expectedTargetLayer)
+                else:
+                    self.assertEqual(mayaUsd.lib.isLayerLocked(stage.GetEditTarget().GetLayer()), False)
+
     def testRefreshSystemLockWithoutCallback(self):
         """
         Test refreshSystemLocks without any callback.