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Unrolled build for rust-lang#131890
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Rollup merge of rust-lang#131890 - printfn:precise-capturing-docs, r=traviscross

Update `use` keyword docs to describe precise capturing

I noticed that the standard library keyword docs for the `use` keyword haven't been updated yet to describe the new precise capturing syntax.
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rust-timer authored Oct 19, 2024
2 parents a2a1206 + be984c1 commit 83f946e
Showing 1 changed file with 39 additions and 7 deletions.
46 changes: 39 additions & 7 deletions library/std/src/keyword_docs.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2146,10 +2146,13 @@ mod unsafe_keyword {}

#[doc(keyword = "use")]
//
/// Import or rename items from other crates or modules.
/// Import or rename items from other crates or modules, or specify precise capturing
/// with `use<..>`.
///
/// Usually a `use` keyword is used to shorten the path required to refer to a module item.
/// The keyword may appear in modules, blocks and even functions, usually at the top.
/// ## Importing items
///
/// The `use` keyword is employed to shorten the path required to refer to a module item.
/// The keyword may appear in modules, blocks, and even functions, typically at the top.
///
/// The most basic usage of the keyword is `use path::to::item;`,
/// though a number of convenient shortcuts are supported:
Expand Down Expand Up @@ -2190,19 +2193,48 @@ mod unsafe_keyword {}
/// // Compiles.
/// let _ = VariantA;
///
/// // Does not compile !
/// // Does not compile!
/// let n = new();
/// ```
///
/// For more information on `use` and paths in general, see the [Reference].
/// For more information on `use` and paths in general, see the [Reference][ref-use-decls].
///
/// The differences about paths and the `use` keyword between the 2015 and 2018 editions
/// can also be found in the [Reference].
/// can also be found in the [Reference][ref-use-decls].
///
/// ## Precise capturing
///
/// The `use<..>` syntax is used within certain `impl Trait` bounds to control which generic
/// parameters are captured. This is important for return-position `impl Trait` (RPIT) types,
/// as it affects borrow checking by controlling which generic parameters can be used in the
/// hidden type.
///
/// For example, the following function demonstrates an error without precise capturing in
/// Rust 2021 and earlier editions:
///
/// ```rust,compile_fail,edition2021
/// fn f(x: &()) -> impl Sized { x }
/// ```
///
/// By using `use<'_>` for precise capturing, it can be resolved:
///
/// ```rust
/// fn f(x: &()) -> impl Sized + use<'_> { x }
/// ```
///
/// This syntax specifies that the elided lifetime be captured and therefore available for
/// use in the hidden type.
///
/// In Rust 2024, opaque types automatically capture all lifetime parameters in scope.
/// `use<..>` syntax serves as an important way of opting-out of that default.
///
/// For more details about precise capturing, see the [Reference][ref-impl-trait].
///
/// [`crate`]: keyword.crate.html
/// [`self`]: keyword.self.html
/// [`super`]: keyword.super.html
/// [Reference]: ../reference/items/use-declarations.html
/// [ref-use-decls]: ../reference/items/use-declarations.html
/// [ref-impl-trait]: ../reference/types/impl-trait.html
mod use_keyword {}

#[doc(keyword = "where")]
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