Since (to a first approximation) every individual who has the expertise and contextual knowledge to really evaluate this issue is a poster on internals.rust-lang.org, its pretty surprising to find this thread on the front page of Hacker News. I imagine some Hacker News users who upvoted this link did so out of technical interest, but I suspect a large portion of the attention comes from some combination of these misconceptions:
- The misconception that this could have a practical impact on users (the code being discussed on the thread is all obviously pathological & contrived).
- The misconception that Rust's type system and standard library never contain soundness issues and that this is an exceptional event (in fact we have a number of longstanding soundness issues).
We have a policy of fixing all soundness issues, so this issue will be fixed. In the meantime, while we decide the best solution, it will have no practical impact on Rust users. And none of the solutions we are considering would involve significant breakage to users, or invalidate any real code.
At a high level: the soundness issue occurs because the Pin API was designed based on certain reasoning about the behavior of pointers. This reasoning would be sound but for the fact that we have allowed certain exceptions in relationship to pointers to what are called the "orphan rules" (which usually enable local reasoning like this). These exceptions allow users to introduce code which, while contrived, allows them to violate the guarantees of the Pin API. Such is life.
Famous last words?
I mean I'm not an expert in Rust and even less in Pin, but I've seen my share of theoretical bugs thought of not possibly having any impact in the real world because of too theoretical. In other areas, when you debug a triple segfault and you understand the crazy conditions that lead to it, or when you render a piece of C++ code conforming instead of technically UB and it then starts to crash when in its UB form it worked perfectly, you start to consider that everything is possible :)
The idea that someone could think an issue is theoretical and then discover it is practically significant is obvious and no insight at all - it reduces to "people are sometimes wrong." I am declaring based on my significant relevant expertise that this issue is not practically important. Your comment contributes nothing but baseless contradiction.