Hey! I just saw this and thought I'd follow up for posterity's sake in case anyone else came across this.

This gets into how we want to define "diffing", but I would say no, no there's not any diffing on the body, manual or otherwise. Per the linked section:

"Before each render, Turbolinks matches all permanent elements by id and transfers them from the original page to the new page, preserving their data and event listeners."

So, at no point is it attempting to determine a difference between two pages. Instead, it simply queries for appropriately tagged elements (from the source code, 'this.bodyElement.querySelectorAll("[id][data-turbolinks-permanent]') and copies those over to the next page.

Thus, it's declarative rather than algorithmic and not what I would consider "diffing" at all. In this context, the parent to my comment stated it's "still having to diff just like react/vdom", which certainly isn't the case.

Cheers!