Compiler does not suggest `move` when it would be appropriate

[grantslatton]

This snippet does not compile with the following error:

pub fn main() {
    |i: u32| { || i };
}

error[E0597]: `i` does not live long enough
 --> src/main.rs:2:19
  |
2 |     |i: u32| { || i };
  |                -- ^ - borrowed value dropped before borrower
  |                |  |
  |                |  borrowed value does not live long enough
  |                capture occurs here
  |
  = note: values in a scope are dropped in the opposite order they are created

https://play.rust-lang.org/?version=stable&mode=debug&edition=2015&gist=2aa8b97e68b9eba4c1b7c0d3f627c386

But adding a move fixes it:

pub fn main() {
    |i: u32| { move || i };
}

I believe the compiler tries to suggest move where appropriate, and it seems that this case has been missed.

[grantslatton]

With Rust 2018 this now provides the correct error message:

error[E0373]: closure may outlive the current function, but it borrows `i`, which is owned by the current function
 --> src/main.rs:2:16
  |
2 |     |i: u32| { || i };
  |                ^^ - `i` is borrowed here
  |                |
  |                may outlive borrowed value `i`
  |
note: closure is returned here
 --> src/main.rs:2:16
  |
2 |     |i: u32| { || i };
  |                ^^^^
help: to force the closure to take ownership of `i` (and any other referenced variables), use the `move` keyword
  |
2 |     |i: u32| { move || i };
  |                ^^^^^^^