Another let_and_return false positive

[antonok-edm]

Summary

There are already a few issues involving let_and_return false positives with E0597, but all of them are closed. I've found another case that still reproduces on Nightly (very similar to the one fixed by #5680).

Lint Name

let_and_return

Reproducer

I tried this code:

struct HasDrop<'i>(core::marker::PhantomData<&'i ()>);

impl<'i> Drop for HasDrop<'i> {
    fn drop(&mut self) {}
}

struct DropIterator<'i>(&'i ());

impl<'i> Iterator for DropIterator<'i> {
    type Item = HasDrop<'i>;
    fn next(&mut self) -> Option<Self::Item> {
        None
    }
}

fn is_valid() -> bool {
    let i = ();
    let mut drop_iter = DropIterator(&i);
    let x = drop_iter.next().is_none();
    x
}

fn main() {
    println!("{}", is_valid());
}

The code runs correctly, printing true to the console. However, there is a single clippy lint reported:

warning: returning the result of a `let` binding from a block
  --> src/main.rs:20:5
   |
19 |     let x = drop_iter.next().is_none();
   |     ----------------------------------- unnecessary `let` binding
20 |     x
   |     ^
   |
   = note: `#[warn(clippy::let_and_return)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#let_and_return
help: return the expression directly
   |
19 ~
20 ~     drop_iter.next().is_none()
   |

After applying the suggestion, the code no longer compiles. The following error is reported:

error[E0597]: `i` does not live long enough
  --> src/main.rs:18:38
   |
18 |     let mut drop_iter = DropIterator(&i);
   |                                      ^^ borrowed value does not live long enough
19 |     drop_iter.next().is_none()
   |     ---------------- a temporary with access to the borrow is created here ...
20 | }
   | -
   | |
   | `i` dropped here while still borrowed
   | ... and the borrow might be used here, when that temporary is dropped and runs the destructor for type `Option<HasDrop<'_>>`
   |
   = note: the temporary is part of an expression at the end of a block;
           consider forcing this temporary to be dropped sooner, before the block's local variables are dropped
help: for example, you could save the expression's value in a new local variable `x` and then make `x` be the expression at the end of the block
   |
19 |     let x = drop_iter.next().is_none(); x
   |     +++++++                           +++

For more information about this error, try `rustc --explain E0597`.

I expected to see this happen:

The original code should not suggest any clippy lints.

Version

rustc 1.59.0-nightly (db9d361a4 2021-11-28)
binary: rustc
commit-hash: db9d361a4731ca0bb48533fab6297a8fea75696f
commit-date: 2021-11-28
host: x86_64-unknown-linux-gnu
release: 1.59.0-nightly
LLVM version: 13.0.0

Additional Labels

@rustbot label +I-suggestion-causes-error