"Undo" doesn't work properly for external geometry creation about freecad

[nazar-pc]

A few more details, trying to delete external edge after such "Undo" results in this:

15:06:41  pyException: Traceback (most recent call last):
  File "<string>", line 1, in <module>
<class 'ValueError'>: Not able to delete an external geometry with the given index: 0
15:06:41  Core#PcieSlotPanelMount: App.getDocument('Core').getObject('Sketch004').delExternal(0)
15:06:41  ViewProviderSketch: Not able to delete an external geometry with the given index: 0

Looks like UI is not synced with some internal data structures or something.

File "<string>", line 1, in <module> is also not particularly helpful for debugging purposes 🙃

[maxwxyz]

is this also happening in the stable 0.21.2 version?
@PaddleStroke @FlachyJoe FYI

[nazar-pc]

Honestly never used stable before and this project created with dev build fails to load in it 🙈

[nazar-pc]

Wanted to test on stable, but couldn't due to FreeCAD/FreeCAD-Bundle#270

[PaddleStroke]

I can reproduce.
I have just tested on 0.20 and the bug is already there.

My guess is that there is a problem in the commands opening/closing.
Probably the creation of external opens a command. Then the linking opens another command before the first is commited. So the first command is not on the undo stack. So when you undo it will undo the linking, then undo again will undo whatever you have done before.

[PaddleStroke]

I had a quick look, it appears that I was wrong. The command is actually reverted correctly.
If you undo, the external geo is still in the list, but if you click on recompute it disappear.

So my new guess is that the Undo does not call rebuildExternalGeometry() but only removes the external geo from the ExternalGeometry list.