IMPL_TRAIT_OVERCAPTURES in rustc_lint::impl_trait_overcaptures - Rust
Description: The `impl_trait_overcaptures` lint warns against cases where lifetime capture behavior will differ in edition 2024.

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## IMPL_TRAIT_OVERCAPTURES

# Static IMPL_TRAIT_OVERCAPTURES

Source

    pub static IMPL_TRAIT_OVERCAPTURES: &Lint

Expand description

The `impl_trait_overcaptures` lint warns against cases where lifetime capture behavior will differ in edition 2024.

In the 2024 edition, `impl Trait`s will capture all lifetimes in scope, rather than just the lifetimes that are mentioned in the bounds of the type. Often these sets are equal, but if not, it means that the `impl Trait` may cause erroneous borrow-checker errors.

#### §Example

ⓘ

    let mut x = vec![];
    x.push(1);

    fn test(x: &Vec<i32>) -> impl Display {
        x[0]
    }

    let element = test(&x);
    x.push(2);
    println!("{element}");

{{produces}}

#### §Explanation

In edition < 2024, the returned `impl Display` doesn’t capture the lifetime from the `&Vec<i32>`, so the vector can be mutably borrowed while the `impl Display` is live.

To fix this, we can explicitly state that the `impl Display` doesn’t capture any lifetimes, using `impl Display + use<>`.