Updated according to the review feedback.

lib/mayaUsd/commands/layerEditorCommand.cpp

@@ -60,8 +60,6 @@ const char kMuteLayerFlag[] = "mt";
 const char kMuteLayerFlagL[] = "muteLayer";
 const char kLockLayerFlag[] = "lk";
 const char kLockLayerFlagL[] = "lockLayer";
-const char kSystemLockLayerFlag[] = "sk";
-const char kSystemLockLayerFlagL[] = "SystemLockLayer";
 
 } // namespace
 

lib/mayaUsd/utils/CMakeLists.txt

@@ -12,7 +12,7 @@ target_sources(${PROJECT_NAME}
         dynamicAttribute.cpp
         editability.cpp
         json.cpp
-		layerLocking.cpp
+        layerLocking.cpp
         layerMuting.cpp
         layers.cpp
         loadRulesAttribute.cpp
@@ -46,7 +46,7 @@ set(HEADERS
     editability.h
     hash.h
     json.h
-	layerLocking.h
+    layerLocking.h
     layerMuting.h
     layers.h
     loadRules.h

lib/mayaUsd/utils/layerLocking.cpp

@@ -62,10 +62,6 @@ void addSystemLockedLayer(const PXR_NS::SdfLayerRefPtr& layer)
         return;
 
     LockedLayers& layers = getLockedLayers();
-    auto          iter = layers.find(layer);
-    if (iter != layers.end()) {
-        return;
-    }
     layers.insert(layer);
 }
 

lib/mayaUsd/utils/layerLocking.h

@@ -35,8 +35,8 @@ namespace MAYAUSD_NS_DEF {
 // stage-level state. So, we need to explicitly save the layer locked state.
 //
 // Additionally, there are multiple levels of locking defined for a layer
-//     1- A layer is locked if layer's permission to edit is set to false
-//     2- A layer is system locked by setting a layer's permission to edit
+//     1- A layer is "Locked" if layer's permission to edit is set to false
+//     2- A layer is "System-Locked" by setting a layer's permission to edit
 //        and a layer's permission to save both to false.
 //
 // However, the USD API for checking permissions is a result of the following
@@ -64,6 +64,13 @@ namespace MAYAUSD_NS_DEF {
 // So we need to hold on to locked layers. We do this in a private global list
 // of locked layers. That list gets cleared when a new Maya scene is created.
 
+enum LayerLockType
+{
+    LayerLock_Unlocked,
+    LayerLock_Locked,
+    LayerLock_SystemLocked
+};
+
 /*! \brief Adds a layer to the system lock list
  */
 MAYAUSD_CORE_PUBLIC

lib/usd/ui/layerEditor/abstractCommandHook.h

@@ -19,6 +19,8 @@
 
 #include "pxr/usd/sdf/layer.h"
 
+#include <mayaUsd/utils/layerLocking.h>
+
 #include <pxr/usd/usd/stage.h>
 
 #include <QtCore/QString>
@@ -79,8 +81,8 @@ class AbstractCommandHook
     // mute or unmute the given layer
     virtual void muteSubLayer(UsdLayer usdLayer, bool muteIt) = 0;
 
-    // lock or unlock the given layer
-    virtual void lockSubLayer(UsdLayer usdLayer, bool lockIt, bool systemLock) = 0;
+    // Sets the lock state on a layer
+    virtual void lockSubLayer(UsdLayer usdLayer, MayaUsd::LayerLockType lockState) = 0;
 
     // starts a complex undo operation in the host app. Please use UndoContext class to safely
     // open/close

lib/usd/ui/layerEditor/layerEditorWidget.cpp

@@ -264,10 +264,10 @@ void LayerEditorWidget::updateButtons()
             if (layer->isSystemLocked()) {
                 count--;
             }
-            // Neither does any anonymous layer whose parent is system locked.
+            // Neither does any anonymous layer whose parent is locked or system-locked.
             // This is because saving an anonymous layer will cause
             // the parent layer to re-path the sub layer with a file name.
-            if (layer->isAnonymous() && layer->appearsSystemLocked()) {
+            if (layer->isAnonymous() && (layer->appearsLocked() || layer->appearsSystemLocked())) {
                 count--;
             }
         }

lib/usd/ui/layerEditor/layerTreeItem.cpp

@@ -281,6 +281,8 @@ bool LayerTreeItem::isLocked() const { return _layer && _layer->PermissionToEdit
 
 bool LayerTreeItem::appearsLocked() const
 {
+    // Note: This is used to indicate that some of the actions
+    // cannot be performed on a layer whose parent is locked.
     auto item = parentLayerItem();
     if (item != nullptr) {
         return item->isLocked();
@@ -293,6 +295,8 @@ bool LayerTreeItem::isSystemLocked() const { return MayaUsd::isLayerSystemLocked
 
 bool LayerTreeItem::appearsSystemLocked() const
 {
+    // Note: This is used to indicate that some of the actions cannot
+    // be performed on a layer whose parent is system-locked.
     auto item = parentLayerItem();
     if (item != nullptr) {
         return item->isSystemLocked();

lib/usd/ui/layerEditor/layerTreeItem.h

@@ -136,11 +136,15 @@ class LayerTreeItem : public QStandardItem
     bool isIncoming() const;
     // is the layer locked?
     bool isLocked() const;
-    // check if this layer is locked
+    // check if this layer appears locked. This means that the layer item itself
+    // may not be locked but by inference some of the action items of the layer
+    // can appear as locked if the parent is locked.
     bool appearsLocked() const;
     // is the layer system locked?
     bool isSystemLocked() const;
-    // check if this layer is system locked
+    // check if this layer appears system locked. This means that the layer item itself
+    // may not be system locked but by inference some of the action items of the layer
+    // can appear as locked if the parent is system locked.
     bool appearsSystemLocked() const;
 
     // used by draw delegate: returns how deep in the hierarchy we are

lib/usd/ui/layerEditor/layerTreeModel.cpp

@@ -582,7 +582,10 @@ void LayerTreeModel::toggleLockLayer(LayerTreeItem* item, bool* forcedState /*=
             return;
     }
 
-    _sessionState->commandHook()->lockSubLayer(item->layer(), !item->isLocked(), false);
+    MayaUsd::LayerLockType toggledLockType = item->isLocked()
+        ? MayaUsd::LayerLockType::LayerLock_Unlocked
+        : MayaUsd::LayerLockType::LayerLock_Locked;
+    _sessionState->commandHook()->lockSubLayer(item->layer(), toggledLockType);
 }
 
 } // namespace UsdLayerEditor

lib/usd/ui/layerEditor/mayaCommandHook.cpp

@@ -210,19 +210,30 @@ void MayaCommandHook::muteSubLayer(UsdLayer usdLayer, bool muteIt)
     executeMel(cmd).asChar();
 }
 
-// lock or unlock the given layer
-void MayaCommandHook::lockSubLayer(UsdLayer usdLayer, bool lockIt, bool systemLock)
+// lock, system-lock or unlock the given layer
+void MayaCommandHook::lockSubLayer(UsdLayer usdLayer, MayaUsd::LayerLockType lockState)
 {
     std::string cmd;
     cmd = "mayaUsdLayerEditor -edit -lockLayer ";
     // 0 = Unlocked
     // 1 = Locked
     // 2 = System Locked
-    if (systemLock) {
+    switch (lockState) {
+    default:
+    case MayaUsd::LayerLockType::LayerLock_Unlocked: {
+        cmd += "0";
+        break;
+    }
+    case MayaUsd::LayerLockType::LayerLock_Locked: {
+        cmd += "1";
+        break;
+    }
+    case MayaUsd::LayerLockType::LayerLock_SystemLocked: {
         cmd += "2";
-    } else {
-        cmd += lockIt ? "1" : "0";
+        break;
     }
+    }
+
     cmd += quote(proxyShapePath());
     cmd += quote(usdLayer->GetIdentifier());
     executeMel(cmd).asChar();

lib/usd/ui/layerEditor/mayaCommandHook.h

@@ -61,8 +61,8 @@ class MayaCommandHook : public AbstractCommandHook
     // mute or unmute the given layer
     void muteSubLayer(UsdLayer usdLayer, bool muteIt) override;
 
-    // lock or unlock the given layer
-    void lockSubLayer(UsdLayer usdLayer, bool lockIt, bool systemLock) override;
+    // lock, system-lock or unlock the given layer
+    void lockSubLayer(UsdLayer usdLayer, MayaUsd::LayerLockType lockState) override;
 
     // starts a complex undo operation in the host app. Please use UndoContext class to safely
     // open/close