Capturing a `mut` variable and then modifying the variable emits a dead-assignment warning

[alco]

fn main() {
    let mut a = 5;
    let adder = |x: int| x + a;
    a = 6;
    println(fmt!("%d", adder(1)));
}

---

λ rust run 07-mut-local-closure.rs
07-mut-local-closure.rs:4:4: 4:5 warning: value assigned to `a` is never read [-W dead-assignment (default)]
07-mut-local-closure.rs:4     a = 6;
                              ^
warning: no debug symbols in executable (-arch x86_64)
7

Expected behavior: no warning because the variable is read from in the subsequent adder(1) call.

[bblum]

Hmm, interesting. This is probably a result of the compiler assuming a function won't do anything interesting between constructing a closure and calling it (or passing it to another function). The fix will be nontrivial.

[pnkfelix]

This is still a problem.

[alexcrichton]

Closing, all captures now count as borrows, disallowing further assignment.