`map_unwrap_or` suggests code that does not compile

Summary

Clippy suggestion does not compile.

The pattern is this:

some_option_that_borrows_mutably
    .map(func)
    .unwrap_or_else(closure_that_borrows_immutably)

After applying the suggestion there is a borrow error.

Lint Name

clippy::map_unwrap_or

Reproducer

I tried this code:

#[warn(clippy::map_unwrap_or)]

fn main() {
    let mut v = [1, 2, 3];
    let w: Vec<_> = v.iter_mut().collect();
    let _ = w.into_iter().next().map(|x| *x).unwrap_or_else(|| *v.iter().max().unwrap());
}

I saw this happen:

warning: called `map(<f>).unwrap_or_else(<g>)` on an `Option` value. This can be done more directly by calling `map_or_else(<g>, <f>)` instead
 --> src/main.rs:6:13
  |
6 |     let _ = w.into_iter().next().map(|x| *x).unwrap_or_else(|| *v.iter().max().unwrap());
  |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `w.into_iter().next().map_or_else(|| *v.iter().max().unwrap(), |x| *x)`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#map_unwrap_or
note: the lint level is defined here
 --> src/main.rs:1:8
  |
1 | #[warn(clippy::map_unwrap_or)]
  |        ^^^^^^^^^^^^^^^^^^^^^

After applying the lint:

#[warn(clippy::map_unwrap_or)]

fn main() {
    let mut v = [1, 2, 3];
    let w: Vec<_> = v.iter_mut().collect();
    let _ = w.into_iter().next().map_or_else(|| *v.iter().max().unwrap(), |x| *x);
}

This is the error:

error[[E0502]](https://doc.rust-lang.org/stable/error_codes/E0502.html): cannot borrow `v` as immutable because it is also borrowed as mutable
 --> src/main.rs:6:46
  |
5 |     let w: Vec<_> = v.iter_mut().collect();
  |                     ------------ mutable borrow occurs here
6 |     let _ = w.into_iter().next().map_or_else(|| *v.iter().max().unwrap(), |x| *x);
  |                                  ----------- ^^  - second borrow occurs due to use of `v` in closure
  |                                  |           |
  |                                  |           immutable borrow occurs here
  |                                  mutable borrow later used by call

For more information about this error, try `rustc --explain E0502`.

Link to playground: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=51f5cf8dafd635de05f2a59d1383287e

Version

rustc 1.73.0-nightly (7bd81ee19 2023-07-13)
binary: rustc
commit-hash: 7bd81ee1902c049691d0a1f03be5558bee51d100
commit-date: 2023-07-13
host: x86_64-pc-windows-msvc
release: 1.73.0-nightly
LLVM version: 16.0.5

Additional Labels

@rustbot label +I-suggestion-causes-error