Retain the tree expansion state after tree refresh

[sandy081]

To reproduce

• Install the jsonOutline extension (Clone it, build it and link it in extensions folder)
• Open any json file, that will show the json outline view
• Expand and collapse some nodes
• Refresh the complete outline / or any node

Expected: Expansion states are preserved.
Observed: Expansion states are reset to initial state.

[sandy081]

Fixed by cb926d5

[letmaik]

To clarify, how are two tree items before and after a refresh matched up to determine that they are the same? It seems each item has a string ID constructed from the tree path.
So:

a
  - b
  - c

Where a has an ID of 0/0:a and a/b has 0/0:a/0:b. However, if I had the following updated tree:

a/0:b
b
  - c

Then the first tree item would likely also have the ID previously assigned to a/b: 0/0:a/0:b. Or is there some escaping going on? I know, it is an artificial example and probably no tree item ever will have such a weird label.
I'm not saying this is an issue, just trying to understand it and find corner cases that may blow up something.

[sandy081]

@letmaik Good point. There is no escaping happening. Had similar assumption that this is not a practical scenario. But do not like to leave this case open. Will do the escaping.

[weinand]

@letmaik I have similar issue with IDs because in my case tree node labels (and hence IDs) change dynamically. Please find a workaround in #40018 (comment). This approach could cover your case as well.

I'd recommend to fix the custom tree by never using the node's label as an ID. Instead assign unique and unchangeable IDs to the TreeItems.