delete tree if delete node is initiated for an empty tree

[philippotto]

Mailable description of changes:

• When deleting the last node of a tree, that tree will not be removed automatically anymore. Instead, the tree will just be empty. To remove that active tree, the "delete" shortcut can be used again.

URL of deployed dev instance (used for testing):

• https://deleteemptytreewithdel.webknossos.xyz/

Steps to test:

• create a new tree and delete it with del again
• test normal delete node functionality

Issues:

• https://discuss.webknossos.org/t/removing-last-node-of-a-tree-also-deletes-tree-but-pressing-del-in-an-empty-tree-doesnt-do-anything/963

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• Ready for review

[philippotto]

@daniel-wer Should be ready for final review :)

[daniel-wer]

LGTM, very nice, works as described. I like that we got rid of the deleteTree side effect :)

[daniel-wer]

Shouldn't t.deepEqual(emptyTreeState, newState) be true here?

[philippotto]

Unfortunately not :( The DiffableMap node collection creates an internal chunk when nodes are added, which is not removed again (it's just emptied). That's why the states differ. Ideally, the equal method would not compare the internal state of the DiffableMap, but I don't know how we can achieve this consistently without doing magic in an own compare-function..

[daniel-wer]

I see, no big deal.

[daniel-wer]

Nice, do you think moving the deleteTreeWithConfirmAction here as well would be sensible?

[philippotto]

Yes, good point, I'll do that!