Compiler gets lifetime scope wrong

[arthurprs]

Please check the code bellow

https://play.rust-lang.org/?gist=c0dd3d93bde346c4bd4d&version=nightly

#![feature(drain)]

use std::sync::{Arc, RwLock};

fn main() {
    let files = RwLock::new(vec![Arc::new(1u32)]);

    // WONT compile
    let a: Vec<_> = files.write().unwrap().drain(..1).collect();

    // WONT compile
    let a: Vec<_> = {
        let mut temp = files.write().unwrap();
        temp.drain(..1).collect()
    };

    // compiles
    let a: Vec<_> = {
        let mut temp = files.write().unwrap();
        let res = temp.drain(..1).collect();
        res
    };

    println!("{:?}", a);
}

I suppose all of them should compile as they do the same thing, but only the last one does.

[steveklabnik]

@gankro is this the expected behavior of drian?

[Gankra]

Nothin' to do with Drain in particular. Just the compiler being suboptimal with temporary lifetimes.

[steveklabnik]

Triage: no change, still reproduces

[memoryruins]

Triage: now compiles on 2018.
2015 errors:

error[E0597]: borrowed value does not live long enough
 --> src/main.rs:9:21
  |
9 |     let a: Vec<_> = files.write().unwrap().drain(..1).collect();
  |                     ^^^^^^^^^^^^^^^^^^^^^^                     - temporary value dropped here while still borrowed
  |                     |
  |                     temporary value does not live long enough
  |
  = note: values in a scope are dropped in the opposite order they are created
  = note: consider using a `let` binding to increase its lifetime

rustc: 1.32.0

[pnkfelix]

Reopening: Our current policy is if the 2015 edition alone suffers from a bug that is scheduled to be fixed by NLL (i.e. tagged NLL-fixed-by-NLL) then we leave such issues open until NLL is turned on in the 2015 edition.