vec_map not build with beta, but compiled with stable and nightly

[Dushistov]

I tried such code:

use std::iter::{Enumerate};
use std::vec;

pub struct IntoIter<V> {
    iter: Enumerate<vec::IntoIter<Option<V>>>,
}

fn into_iter_covariant<'a, T>(iter: IntoIter<&'static T>) -> IntoIter<&'a T> { iter }

fn main() {
}

rustup run beta rustc test_code.rs give error:

error[E0308]: mismatched types
 --> test_code.rs:9:80
  |
9 | fn into_iter_covariant<'a, T>(iter: IntoIter<&'static T>) -> IntoIter<&'a T> { iter }
  |                                                                                ^^^^ lifetime mismatch
  |
  = note: expected type `IntoIter<&'a T>`
  = note:    found type `IntoIter<&'static T>`
note: the lifetime 'a as defined on the block at 9:77...
 --> test_code.rs:9:78
  |
9 | fn into_iter_covariant<'a, T>(iter: IntoIter<&'static T>) -> IntoIter<&'a T> { iter }
  |                                                                              ^^^^^^^^
  = note: ...does not necessarily outlive the static lifetime

error: aborting due to previous error

$ rustup run beta rustc --version
rustc 1.12.0-beta.1 (822166b84 2016-08-16)

But stable and nightly version of compiler compile such code just fine:

$ rustup run nightly rustc --version
rustc 1.13.0-nightly (499484f56 2016-08-18)
$ rustup run stable rustc --version
rustc 1.11.0 (9b21dcd6a 2016-08-15)

This bug prevent to compile vec_map crate (from which I extract rust code above),
and racer depend on vec_map, so I can not compile racer project also.

[Mark-Simulacrum]

Duplicate of #35721. Thanks for reporting, though!

[Dushistov]

@Mark-Simulacrum I am not familiar with internal rules, but why #35721 marked as closed (this why I not found it), but fix not merged to beta?

[Mark-Simulacrum]

The fix was nominated for a beta backport, but so far no backport has been implemented; I'm not sure what the project policy is regarding whether to leave issues open/closed when they need backporting.