NLL: error from get-opts crate

[nikomatsakis]

In #47596, @SimonSapin reported several NLL errors in dependencies of the servo crate. @lqd later minimized one of those errors into this example:

#![feature(nll)]

enum SplitWithinState { A, B }

fn each_split_within() {
    let mut state = SplitWithinState::A;
    let mut closure = || { state = SplitWithinState::A };
    if let SplitWithinState::A = state {
    }
    closure();
}

fn main() {}

which yields:

error[E0503]: cannot use `state` because it was mutably borrowed
 --> src/main.rs:8:12
  |
7 |     let mut closure = || { state = SplitWithinState::A };
  |                       ---------------------------------- borrow of `state` occurs here
8 |     if let SplitWithinState::A = state {
  |            ^^^^^^^^^^^^^^^^^^^ use of borrowed `state`

error: aborting due to previous error

That said, at first glance, this looks like it might be a bug fix -- the closure is assigning to state, so it has a mutable borrow, and the if let is testing it. Pretty sure this is #45045.

[nikomatsakis]

Going to close as duplicate of #45045 (and hence NLL is acting correctly)

[SimonSapin]

Thanks for working out the details. It looks like this is already fixed in git upstream, filed rust-lang/getopts#60

[SimonSapin]

… or not. rust-lang/getopts#61