needless_collect false positives around borrowing

Lint name: needless_collect

I tried this code:

struct Foo(Vec<u8>);

impl Foo {
    fn get_iterator(&self) -> impl Iterator<Item = u8> {
        let items: Vec<_> = self.0.iter().filter(|x| **x > 0).copied().collect();
        items.into_iter()
    }
}

(playpen)

I expected to see this happen: No lint, because removing the collect produces an iterator that borrows from self

Instead, this happened:

warning: avoid using `collect()` when not needed
 --> src/main.rs:5:72
  |
5 |         let items: Vec<_> = self.0.iter().filter(|x| **x > 0).copied().collect();
  |                                                                        ^^^^^^^
6 |         items.into_iter()
  |         ----------------- 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
  |
5 |         
6 |         self.0.iter().filter(|x| **x > 0).copied()
  |

Meta

• cargo clippy -V: clippy 0.1.54 (a178d03 2021-07-26)
• rustc -Vv:

rustc 1.54.0 (a178d0322 2021-07-26)
binary: rustc
commit-hash: a178d0322ce20e33eac124758e837cbd80a6f633
commit-date: 2021-07-26
host: x86_64-unknown-linux-gnu
release: 1.54.0
LLVM version: 12.0.1rustc 1.54.0 (a178d0322 2021-07-26)
binary: rustc
commit-hash: a178d0322ce20e33eac124758e837cbd80a6f633
commit-date: 2021-07-26
host: x86_64-unknown-linux-gnu
release: 1.54.0
LLVM version: 12.0.1

Reproduce the needless_collect warning with the Rust example in the issue by running cargo clippy. Start at the needless_collect lint entry point, then add coverage for the borrowing case so the lint does not suggest removing a collect when that would return an iterator borrowing from self.