✨ add parents to regexp visitor

[connor4312]

Duplicating mysticatea#18

[MichaelDeBoey]

@connor4312 Please rebase your branch onto latest main & resolve conflicts

[RunDevelopment]

Cool PR!

Question: Is it intentional that the parents array does not include the parents of the root node (= the node we call RegExpVisitor#visit on)? This seems strange to me, because it means that parents does not contain all ancestors of a node. In other words, I assumed !currentNode.parent || currentNode.parent == parents.at(-1) to be an invariant.

About the name "parents": a parent is typically the first direct ancestor of a node. So maybe we should name the parameter ancestors? I'm not sure which one is better, though.

Also, maybe we could do that better than Node[] for the type of parents? E.g. we know that the parents array of a Pattern node can only contain a RegExpLiteral node, and we know that the parents array of a quantifier can't contain a Character node. I think it would be nice if we had e.g. onGroupEnter?(node: Group, parents: readonly Ancestor<Group>[]): void (using the Ancestor type from here in this example).
I think this would make it easier for people to use the parents array, since TS has a better idea about its contents.

[ota-meshi]

I don't think we need to add this parameter.
You can already easily access the parent node using node.parent.
What use cases are new parents useful for?

[connor4312]

ah, you're right. Somehow missed that however many years ago I wrote this.