Unexpected region for local data ReStatic

[leonardo-m]

#![feature(nll)]

fn fibs(n: u32) -> impl Iterator<Item=u128> {
    (0 .. n)
    .scan((0, 1), |st, _| {
        *st = (st.1, st.0 + st.1);
        Some(*st)
    })
    .map(&|(f, _)| f)
}

fn main() {
    println!("{:?}", fibs(10).collect::<Vec<_>>());
}

error: internal compiler error: unexpected region for local data ReStatic
 --> ...\test.rs:9:11
  |
9 |     .map(&|(f, _)| f)
  |           ^^^^^^^^^^

error: aborting due to previous error

rustc 1.26.0-nightly (06fa27d7c 2018-04-01)
binary: rustc
commit-hash: 06fa27d7c84a21af8449e06f3c50b243c4d5a7ad
commit-date: 2018-04-01
host: x86_64-pc-windows-gnu
release: 1.26.0-nightly
LLVM version: 6.0

[nikomatsakis]

Still an ICE. Adding as Preview 2 but I'm not sure the cause yet.

[matthewjasper]

Successfully compiles now that we don't run AST borrowck when we don't need to.

This code compiles because the closure is promoted to a static, is this something that we want to be visible to the user?

[nikomatsakis]

I see, I see. Yes, that is expected to be exposed to the user.

[nikomatsakis]

I guess we can close this then as Working as Expected. Nice job @spastorino, you get the credit for fixing this one :)

[nikomatsakis]

Er, I'll leave open because (as @matthewjasper noted) we still need a test

[davidtwco]

Submitted #52809 with the test that is remaining for this issue.