Fix node deletion being too greedy

[Daniel53245]

Closes #2606

As mentioned in #2606 , in node editor mode, deleting nodes sometime results unwanted deletion of parent nodes.

This PR examines the algorithm for deletion and modified its behavior. Now, it will not cause the deletion in #2606, but I haven't tested it for other cases. I will put this as a draft PR till I am sure it works for other conditions

[Daniel53245]

Fix Node Deletion is too greedy

Original Code

https://github.com/GraphiteEditor/Graphite/blob/d39308c048cc439715943ff487294ffccaf12c70/editor/src/messages/portfolio/document/utility_types/network_interface.rs#L4177//

The original code for greedy node deletion was a graph search algorithm in rust. It iterates each upstream node for the nodes marked for deletion.

For one of the upstream node it checks all the child it connected to

1. the child is marked for deletion, search in this branch is stopped (will result deletion of upstream node if all the childs falls in this category)
2. the child is not marked for deletion, continue search the grandchildren

Cause of the original bug

As mentioned in the original issue, following images describes one of the condition that the algorithm fails and deleted "Identity" node while it is used by other nodes

During the deletion, the original algorithm check all the downstream node for the "Identity", it confirms that "equals is marked for deletion by the user. The algorithm searches through "Greater Than" and "Switch". A the point it reaches "Switch", the issue happened.

The line

let Some(downstream_nodes) = outward_wires.get(&current_node) else { continue };

"Switch" node does not have any child, this line continues the loop. The algorithm ignores "Switch" and mistake that all downstream nodes of "Identity" are marked for deletion

Modification

The original algorithm does a recursive search through the graph. I modified that algorithm such that it would mark the upstream node not for deletion once it reach a non-deletion downstream node. This is achieve by modifying line

if !delete_nodes.contains(downstream_id) {
	stack.push(downstream_node_output);
}

to

if !delete_nodes.contains(downstream_id) {
	can_delete = false;
	break;
}

Test of the modified code

I tested modified code in many situations

Deletion of the node will not cause deletion of any other node

Deletion of "Switch" cause both upstream node deleted

Deletion of "Logical Or" will not delete any other node

Sandwiched deletion will not cause the middle node to be deleted

Deleting last node of the chain will cause the deletion of all upstream nodes

[otdavies]

!build

[github-actions]

📦 Build Complete for 1d1d22e
https://18bdf8cb.graphite.pages.dev

[Keavon]

Thank you!

[Keavon]

Hi @Daniel53245, thanks again for this code contribution to the project! We're still hoping you will respond to the request to relicense this code. Please see #4208 ASAP, thank you!

[Keavon]

Hi @Daniel53245, we're grateful of your past code contribution to Graphite, but unless we hear from you by the end of this weekend with agreement about relicensing your code to include the MIT license, we will begin steps to remove your code contributions so that you will no longer be a Graphite code contributor. We'd much rather avoid this outcome, so please respond now.

To agree, simply log into your GitHub account, visit #4208, and copy-paste this into a comment:

"I license my past and future contributions to Graphite under the dual MIT/Apache-2.0 license, allowing licensees to choose either at their option."

If you're hesitant because you disagree or have questions, feel free to respond with another message; we'll do our best to answer your questions or concerns. More explanation is at the top of the linked thread if you're confused. So far, 164 contributors have agreed and you are among the 11% remaining whom we are still hoping to hear from before we begin removing your code from the project starting this Monday. (If you only see this later than Monday, your future belated response will still be appreciated.)

Thank you for your cooperation and support of open source, and we hope you'll help us keep your valued contributions in-tact.