Matching to Houdini build 18.5.29.

src/houdini/lib/H_USD/HUSD/XUSD_Data.C

@@ -1025,27 +1025,37 @@ XUSD_Data::addLayer(const XUSD_LayerAtPath &layer,
 	}
     }
 
-    // Release the current write lock.
-    afterRelease();
-
-    // Tag the layer with our creator node, if it hasn't been set already.
-    // Then disallow further edits of the layer.
-    if (layer.isLayerAnonymous() &&
-	!HUSDgetCreatorNode(layer.myLayer, node_path))
-	HUSDsetCreatorNode(layer.myLayer, myDataLock->getLockedNodeId());
-    layer.myLayer->SetPermissionToEdit(false);
-
     // The position argument is 0 for the strongest layer, -1 for the weakest.
     // If the layer is meant to be editable, it must be the strongest layer.
     // Adjust the position to reflect the fact that mySourceLayers is ordered
     // weakest to strongest, so we must reverse the position argument.
+    // We figure this out before releasing the lock in case the active layer
+    // gets removed when we release the lock. We want the position to be
+    // relative to the list of layers including the active layer, otherwise
+    // the layer indices won't match up with what the users sees (which always
+    // includes an active layer).
     if (add_layer_op == XUSD_ADD_LAYER_EDITABLE)
 	position = mySourceLayers.size();
     else if (position >= 0 && position <= mySourceLayers.size())
 	position = mySourceLayers.size() - position;
     else
 	position = 0;
 
+    // Release the current write lock.
+    afterRelease();
+
+    // Make sure the removal of the active layer didn't make the calculated
+    // position value invalid.
+    if (position > mySourceLayers.size())
+	position = mySourceLayers.size();
+
+    // Tag the layer with our creator node, if it hasn't been set already.
+    // Then disallow further edits of the layer.
+    if (layer.isLayerAnonymous() &&
+	!HUSDgetCreatorNode(layer.myLayer, node_path))
+	HUSDsetCreatorNode(layer.myLayer, myDataLock->getLockedNodeId());
+    layer.myLayer->SetPermissionToEdit(false);
+
     // Add the sublayer to the stack. Then advance our active layer to point
     // to this new layer (if we want to be allowed to edit it further), oro to
     // one layer past this new sublayer. It is up to the caller to decide if it
@@ -1102,13 +1112,14 @@ XUSD_Data::removeLayer(const std::string &filepath)
 	    // we have to flip the index value when deciding which stage
 	    // sublayer to remove. Do this before releasing the lock in case
 	    // the active layer gets removed, which does not affect the stage
-	    // sublayers.
+	    // sublayers. Note that we don't need to worry about placeholder
+            // layers, because they are always the strongest layers. And what
+            // we know is that we want to remove the i'th weakest layer. This
+            // can be safely assumed to be i spots from the end of the array
+            // of layers on the stage.
 	    int stagesize = myStage->GetRootLayer()->GetNumSubLayerPaths();
 	    int stageidx = stagesize - i - 1;
 
-	    // Just verify that the source layers and stage sublayers match.
-	    UT_ASSERT(mySourceLayers.size() == stagesize);
-
 	    // Release the current write lock.
 	    // Note that we don't need to add a layer to the write lock tag.
 	    // We are either removing some non-current layer, in which case