Allow disabling undo on save

The transaction system does not scale on large scale or complex remove_deep deletions. So if you want to delete a mesh with many thousands of vertices, it becomes very, very slow. Unfortunately we cannot also clear Blender's undo history, so this advanced feature should be used carefully.

Tested:

 - deleting 250 average objects: 264s before, 246s after (6.8% faster)
 - deleting 1 object with 6,000 vertices: 5 minutes and counting (basically impractical) before, 11s after

src/blenderbim/blenderbim/bim/module/project/operator.py

@@ -828,7 +828,16 @@ class ExportIFC(bpy.types.Operator):
         return {"RUNNING_MODAL"}
 
     def execute(self, context):
-        return IfcStore.execute_ifc_operator(self, context)
+        if context.scene.BIMProjectProperties.should_disable_undo_on_save:
+            old_history_size = tool.Ifc.get().history_size
+            old_undo_steps = context.preferences.edit.undo_steps
+            tool.Ifc.get().history_size = 0
+            context.preferences.edit.undo_steps = 0
+        IfcStore.execute_ifc_operator(self, context)
+        if context.scene.BIMProjectProperties.should_disable_undo_on_save:
+            tool.Ifc.get().history_size = old_history_size
+            context.preferences.edit.undo_steps = old_undo_steps
+        return {"FINISHED"}
 
     def _execute(self, context):
         start = time.time()

src/blenderbim/blenderbim/bim/module/project/prop.py

@@ -159,6 +159,7 @@ class BIMProjectProperties(PropertyGroup):
     false_origin: StringProperty(name="False Origin", default="0,0,0")
     element_offset: IntProperty(name="Element Offset", default=0)
     element_limit: IntProperty(name="Element Offset", default=30000)
+    should_disable_undo_on_save: BoolProperty(name="Disable Undo When Saving (Faster saves, no undo for you!)", default=False)
     links: CollectionProperty(name="Links", type=Link)
     active_link_index: IntProperty(name="Active Link Index")
     export_schema: EnumProperty(items=get_export_schema, name="IFC Schema")

src/ifcopenshell-python/ifcopenshell/file.py

@@ -203,7 +203,8 @@ class file(object):
             self.history.pop(0)
 
     def begin_transaction(self):
-        self.transaction = Transaction(self)
+        if self.history_size:
+            self.transaction = Transaction(self)
 
     def end_transaction(self):
         if self.transaction: