`DOMEditor.toSlatePoint` could find a point in a parent editor

[christianhg]

Hi there 👋

I was investigating a gnarly issue in an app that unfortunately is closed source and quite difficult to create a reproduction sandbox from. In any case, I thought I would write up what I found about how DOMEditor.toSlatePoint can end up producing a wrong point in a nested editor scenario:

1. If the editor is read-only and therefore is marked as contenteditable="false" then nonEditableNode could end up being the editor itself:

   slate/packages/slate-dom/src/plugin/dom-editor.ts

   Lines 722 to 725 in a8fc9a4

   	const nonEditableNode =
   	potentialNonEditableNode && editorEl.contains(potentialNonEditableNode)
   	? potentialNonEditableNode
   	: null

2. And if there's no leafNode because the event origins from a non-leaf then we end up in the } else if (nonEditableNode) { clause:

   slate/packages/slate-dom/src/plugin/dom-editor.ts

   Line 726 in a8fc9a4

   let leafNode = parentNode.closest('[data-slate-leaf]')

3. Inside this clause, if the editor is nested inside another editor then nonEditableNode.closest('[data-slate-node="element"]') can potentially find a node inside the parent editor:

   slate/packages/slate-dom/src/plugin/dom-editor.ts

   Lines 811 to 813 in a8fc9a4

   	const elementNode = nonEditableNode.closest(
   	'[data-slate-node="element"]'
   	)

4. Further down DOMEditor.toSlatePoint, DOMEditor.toSlateNode is called:

   slate/packages/slate-dom/src/plugin/dom-editor.ts

   Line 912 in a8fc9a4

   const slateNode = DOMEditor.toSlateNode(editor, textNode!)

5. But since this method uses the global ELEMENT_TO_NODE WeakMap, it will probably return a Slate node even though it's from another editor:

   slate/packages/slate-dom/src/plugin/dom-editor.ts

   Line 682 in a8fc9a4

   const node = domEl ? ELEMENT_TO_NODE.get(domEl as HTMLElement) : null

I suppose this is a bug? Could it be mitigated it by adding a check to see if nonEditableNode is the editor itself and then return the start or end of the editor depending on the searchDirection?