Reassignment not considered by borrow rules

[tkoeppe]

This may be a duplicate, but I haven't seen this resolved anywhere in the similar-looking issues. With the current nightly, the following borrow is not allowed:

let mut a = 2u;
let mut p = &mut a;
p = &mut a; // Error here: "a already borrowed"

In terms of lifetimes, the first borrow should end by the time p is being reassigned to. However, in the current version of Rust, the borrow is considered to be taken out as long as p is alive.

What is the current state of this, and are there plans to change the semantics of assignment to be able to end borrows?

[alexcrichton]

I think this is a duplicate of #6393 which should allow the compiler to detect that the liveness of the original value of p is immediately dead after assignment (allowing a reassignment and a re-borrow of a).

[tkoeppe]

That looks right, thanks!