Core: Add Gui::Document::getTreeRootObjects()

src/Mod/Assembly/CommandInsertLink.py

@@ -203,7 +203,8 @@ class TaskAssemblyInsertLink(QtCore.QObject):
                         ):
                             process_objects(obj.OutList, objItem)
 
-            process_objects(doc.RootObjectsIgnoreLinks, docItem)
+            guiDoc = Gui.getDocument(doc.Name)
+            process_objects(guiDoc.TreeRootObjects, docItem)
             self.form.partList.expandAll()
 
     def onFilterChange(self):

src/Mod/Assembly/UtilsAssembly.py

@@ -308,7 +308,7 @@ def getGlobalPlacement(targetObj, container=None):
 
 
 def isThereOneRootAssembly():
-    for part in App.activeDocument().RootObjectsIgnoreLinks:
+    for part in Gui.activeDocument().TreeRootObjects:
         if part.TypeId == "Assembly::AssemblyObject":
             return True
     return False