needless_lifetimes suggestion forgets to remove some lifetimes

[matthiaskrgr]

Summary

clippy leaves in one of lifetimes and thus the code fails to compile

9 - fn f<'a>(PhantomData::<&'a u8>: PhantomData<&'a u8>) {}
9 + fn f(PhantomData::<&'a u8>: PhantomData<&u8>) {}

Reproducer

I tried this code:

#![allow(dead_code)]
use std::marker::PhantomData;

fn f<'a>(PhantomData::<&'a u8>: PhantomData<&'a u8>) {}

fn main() {}

I expected to see this happen:

warning: the following explicit lifetimes could be elided: 'a
 --> src/main.rs:9:1
  |
9 | fn f<'a>(PhantomData::<&'a u8>: PhantomData<&'a u8>) {}
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes
  = note: `#[warn(clippy::needless_lifetimes)]` on by default
help: elide the lifetimes
  |
9 - fn f<'a>(PhantomData::<&'a u8>: PhantomData<&'a u8>) {}
9 + fn f(PhantomData::<&u8>: PhantomData<&u8>) {}

Instead, this happened:

warning: the following explicit lifetimes could be elided: 'a
 --> src/main.rs:9:1
  |
9 | fn f<'a>(PhantomData::<&'a u8>: PhantomData<&'a u8>) {}
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes
  = note: `#[warn(clippy::needless_lifetimes)]` on by default
help: elide the lifetimes
  |
9 - fn f<'a>(PhantomData::<&'a u8>: PhantomData<&'a u8>) {}
9 + fn f(PhantomData::<&'a u8>: PhantomData<&u8>) {}

Version

rustc 1.70.0-nightly (8a73f50d8 2023-03-11)
binary: rustc
commit-hash: 8a73f50d875840b8077b8ec080fa41881d7ce40d
commit-date: 2023-03-11
host: x86_64-unknown-linux-gnu
release: 1.70.0-nightly
LLVM version: 15.0.7

Additional Labels

No response

[DaniPopes]

Encountered the same with an impl in return position:

pub fn f<'a>(slice: &'a [u8]) -> impl Iterator<Item = &'a u8> + 'a {
    slice.iter()
}

needless_lifetimes suggestion:

warning: the following explicit lifetimes could be elided: 'a
 --> src/main.rs:1:1
  |
1 | pub fn f<'a>(slice: &'a [u8]) -> impl Iterator<Item = &'a u8> + 'a {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes
  = note: `#[warn(clippy::needless_lifetimes)]` on by default
help: elide the lifetimes
  |
1 - pub fn f<'a>(slice: &'a [u8]) -> impl Iterator<Item = &'a u8> + 'a {
1 + pub fn f(slice: &[u8]) -> impl Iterator<Item = &'_ u8> + 'a {
  |

Reported errors:

The following errors were reported:
error[E0261]: use of undeclared lifetime name `'a`
 --> src/main.rs:1:58
  |
1 | pub fn f(slice: &[u8]) -> impl Iterator<Item = &'_ u8> + 'a {
  |         -                                                ^^ undeclared lifetime
  |         |
  |         help: consider introducing lifetime `'a` here: `<'a>`

error: lifetime may not live long enough
 --> src/main.rs:2:5
  |
1 | pub fn f(slice: &[u8]) -> impl Iterator<Item = &'_ u8> + 'a {
  |                 - let's call the lifetime of this reference `'1`
2 |     slice.iter()
  |     ^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'static`
  |
help: to declare that `impl std::iter::Iterator<Item = &u8> + '_` captures data from argument `slice`, you can add an explicit `'_` lifetime bound
  |
1 | pub fn f(slice: &[u8]) -> impl Iterator<Item = &'_ u8> + 'a + '_ {
  |                                                             ++++

Version

rustc 1.71.0-nightly (7908a1d65 2023-04-17)
binary: rustc
commit-hash: 7908a1d65496b88626e4b7c193c81d777005d6f3
commit-date: 2023-04-17
host: x86_64-unknown-linux-gnu
release: 1.71.0-nightly
LLVM version: 16.0.2