Workaround for DAG invalidation - remove all expressions before deleting an object.

src/Mod/Path/PathScripts/PathJob.py

@@ -151,6 +151,7 @@ class ObjectJob:
         while obj.Operations.Group:
             op = obj.Operations.Group[0]
             if not op.ViewObject or not hasattr(op.ViewObject.Proxy, 'onDelete') or op.ViewObject.Proxy.onDelete(op.ViewObject, ()):
+                PathUtil.clearExpressionEngine(op)
                 doc.removeObject(op.Name)
         obj.Operations.Group = []
         doc.removeObject(obj.Operations.Name)
@@ -158,22 +159,27 @@ class ObjectJob:
         # stock could depend on Base
         if obj.Stock:
             PathLog.debug('taking down stock')
+            PathUtil.clearExpressionEngine(obj.Stock)
             doc.removeObject(obj.Stock.Name)
             obj.Stock = None
         # base doesn't depend on anything inside job
         if obj.Base:
             PathLog.debug('taking down base')
             if isResourceClone(obj, 'Base'):
+                PathUtil.clearExpressionEngine(obj.Base)
                 doc.removeObject(obj.Base.Name)
             obj.Base = None
         # Tool controllers don't depend on anything
         PathLog.debug('taking down tool controller')
         for tc in obj.ToolController:
+            PathUtil.clearExpressionEngine(tc)
             doc.removeObject(tc.Name)
         obj.ToolController = []
         # SetupSheet
+        PathUtil.clearExpressionEngine(obj.SetupSheet)
         doc.removeObject(obj.SetupSheet.Name)
         obj.SetupSheet = None
+        return True
 
     def fixupResourceClone(self, obj, name, icon):
         if not isResourceClone(obj, name, name) and not isArchPanelSheet(obj):

src/Mod/Path/PathScripts/PathOpGui.py

@@ -30,6 +30,7 @@ import PathScripts.PathGui as PathGui
 import PathScripts.PathLog as PathLog
 import PathScripts.PathSelection as PathSelection
 import PathScripts.PathOp as PathOp
+import PathScripts.PathUtil as PathUtil
 import PathScripts.PathUtils as PathUtils
 import importlib
 
@@ -161,6 +162,10 @@ class ViewProvider(object):
         if self.panel:
             self.panel.updateData(obj, prop)
 
+    def onDelete(self, vobj, arg2=None):
+        PathUtil.clearExpressionEngine(vobj.Object)
+        return True
+
 class TaskPanelPage(object):
     '''Base class for all task panel pages.'''
 
@@ -767,6 +772,7 @@ class TaskPanel(object):
         FreeCAD.ActiveDocument.abortTransaction()
         if self.deleteOnReject:
             FreeCAD.ActiveDocument.openTransaction(translate("Path", "Uncreate AreaOp Operation"))
+            PathUtil.clearExpressionEngine(self.obj)
             FreeCAD.ActiveDocument.removeObject(self.obj.Name)
             FreeCAD.ActiveDocument.commitTransaction()
         self.cleanup(resetEdit)

src/Mod/Path/PathScripts/PathToolController.py

@@ -28,6 +28,7 @@ import Part
 import Path
 import PathScripts
 import PathScripts.PathLog as PathLog
+import PathScripts.PathUtil as PathUtil
 
 from FreeCAD import Units
 from PySide import QtCore
@@ -191,6 +192,10 @@ class ViewProvider:
         vobj.setEditorMode('BoundingBox', mode)
         vobj.setEditorMode('Selectable', mode)
 
+    def onDelete(self, vobj, args=None):
+        PathUtil.clearExpressionEngine(vobj.Object)
+        return True
+
     def updateData(self, vobj, prop):
         # this is executed when a property of the APP OBJECT changes
         pass

src/Mod/Path/PathScripts/PathUtil.py

@@ -87,3 +87,12 @@ def getPublicObject(obj):
             return getPublicObject(body)
     return obj
 
+def clearExpressionEngine(obj):
+    '''clearExpressionEngine(obj) ... removes all expressions from obj.
+
+There is currently a bug that invalidates the DAG if an object
+is deleted that still has one or more expressions attached to it.
+Use this function to remove all expressions before deletion.'''
+    if hasattr(obj, 'ExpressionEngine'):
+        for attr,expr in obj.ExpressionEngine:
+            obj.setExpression(attr, None)