FP: needless_for_each causes type inference problems

[matthiaskrgr]

Summary

.

Lint Name

needless_for_each

Reproducer

I tried this code:

#![feature(generators)]
// #59620
fn nested_closures() {
    let mut i = 0;
    [].iter().for_each(|_: &i32| {
        [].iter().for_each(move |_: &i32| {
            i += 1;
        });
    });
}

fn main() {}

I saw this happen:
cargo clippy --fix -- -Aclippy::all -Wclippy::needless_for_each

warning: failed to automatically apply fixes suggested by rustc to crate `clpy`

after fixes were automatically applied the compiler reported errors within these files:

  * src/main.rs

This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag

The following errors were reported:
error[E0282]: type annotations needed
  --> src/main.rs:11:21
   |
11 |         for _ in [].iter() {
   |                     ^^^^ cannot infer type

error: aborting due to previous error

For more information about this error, try `rustc --explain E0282`.
Original diagnostics will follow.

warning: unused variable: `i`
  --> src/main.rs:12:13
   |
12 |             i += 1;
   |             ^
   |
   = help: did you mean to capture by reference instead?
   = note: `#[warn(unused_variables)]` on by default

warning: function `nested_closures` is never used
 --> src/main.rs:8:4
  |
8 | fn nested_closures() {
  |    ^^^^^^^^^^^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: needless use of `for_each`
  --> src/main.rs:10:5
   |
10 | /     [].iter().for_each(|_: &i32| {
11 | |         [].iter().for_each(move |_: &i32| {
12 | |             i += 1;
13 | |         });
14 | |     });
   | |_______^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_for_each
   = note: requested on the command line with `-W clippy::needless-for-each`
help: try
   |
10 ~     for _ in [].iter() {
11 +         [].iter().for_each(move |_: &i32| {
12 +             i += 1;
13 +         });
14 +     }
   |

warning: needless use of `for_each`
  --> src/main.rs:11:9
   |
11 | /         [].iter().for_each(move |_: &i32| {
12 | |             i += 1;
13 | |         });
   | |___________^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_for_each
help: try
   |
11 ~         for _ in [].iter() {
12 +             i += 1;
13 +         }
   |

warning: `clpy` (bin "clpy") generated 4 warnings (run `cargo fix --bin "clpy"` to apply 2 suggestions)
warning: `clpy` (bin "clpy" test) generated 4 warnings (4 duplicates)
    Finished dev [unoptimized + debuginfo] target(s) in 0.52s

Version

rustc 1.67.0-nightly (c5d82ed7a 2022-11-19)
binary: rustc
commit-hash: c5d82ed7a4ad94a538bb87e5016e7d5ce0bd434b
commit-date: 2022-11-19
host: x86_64-unknown-linux-gnu
release: 1.67.0-nightly
LLVM version: 15.0.4

Additional Labels

No response