False Positive for needless_collect with two mutable borrows

Summary

The applied lint fails to compile due to a Map created with items created from mutable borrows.

Lint Name

clippy::needless_collect

Reproducer

I tried this code:

...
let v: Vec<char> = (0..num)
    .map(|_| cmap.get_mut(origin - 1).unwrap().pop().unwrap())
    .collect();
cmap.get_mut(target - 1)
    .unwrap()
    .extend(v.into_iter().rev());
...
}

I saw this happen:

warning: avoid using `collect()` when not needed
  --> src\days\day_05.rs:28:18
   |
28 |                 .collect();
   |                  ^^^^^^^
...
31 |                 .extend(v.into_iter().rev());
   |                         ------------- the iterator could be used here instead
   |
   = note: `#[warn(clippy::needless_collect)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_collect
help: use the original Iterator instead of collecting it and then producing a new one
   |
26 ~
27 |             cmap.get_mut(target - 1)
28 |                 .unwrap()
29 ~                 .extend((0..num)
30 ~                 .map(|_| cmap.get_mut(origin - 1).unwrap().pop().unwrap()).rev());
   |

I expected to see this happen:

No warning.

Version

rustc 1.65.0 (897e37553 2022-11-02)
binary: rustc
commit-hash: 897e37553bba8b42751c67658967889d11ecd120
commit-date: 2022-11-02
host: x86_64-pc-windows-msvc
release: 1.65.0
LLVM version: 15.0.0

Additional Labels

No response

Start by reproducing the warning from the Rust snippet in the issue, focusing on the clippy::needless_collect lint and its suggested iterator rewrite. Trace how the lint handles the two mutable borrows; done means this valid pattern is no longer warned about while the lint still reports cases where collecting is unnecessary.