needless_lifetimes false positive, which leads to unsound code

[matklad]

Summary

See jeromefroe/lru-rs#153

Reproducer

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Version

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Additional Labels

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[Jarcho]

Is there a reason pub fn peek_lru(&self) -> Option<(&K, &V)> is wrong? The lint could use a suggestion.

[matklad]

Hm, actually you are right! The error message isn't inherently misleading:

    Checking lru v0.7.8 (/home/matklad/p/lru-rs)
error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
   --> src/lib.rs:489:5
    |
489 |     pub fn get_or_insert<'a, F>(&'a mut self, k: K, f: F) -> &'a V
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D clippy::needless-lifetimes` implied by `-D warnings`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes

we can fully rely on elision here. But yeah, I think adding a suggestion here would help to make sure that all 'a's are removed