The data backtrace?

I don't know if this exists but, given rust, I think it'll be important to have. I was just debugging an issue where a value passed to a function was not correct and I needed to know where it was changed. Because of the borrow checker it could be unlikely this would appear in a stack frame backtrace!

Thus it's important to have a tool that would be able to list where a value comes from.

This is something that rr can do: