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Rollup merge of #123393 - aDotInTheVoid:ast-p-docs, r=Nilstrieb

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rustc_ast: Update `P<T>` docs to reflect mutable status.

`P<T>` has implemented `DerefMut` since #54277. While this was lamented at the time [1], rustc now relies on it extensively via the many implementors of MutVisitor [2].

Updates the docs to reflect that `P<T>` is fundamentally mutable, and a few other cleanups to make them nicer to browse.

[1]: https://github.com/rust-lang/rust/pull/54277#discussion_r257181754
[2]: https://doc.rust-lang.org/1.77.1/nightly-rustc/rustc_ast/mut_visit/trait.MutVisitor.html#implementors

r? `@Nilstrieb`
This commit is contained in:
Matthias Krüger 2024-04-03 17:15:49 +02:00 committed by GitHub
commit 0c11f13a57
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1 changed files with 7 additions and 9 deletions
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16
compiler/rustc_ast/src/ptr.rs
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@ -1,6 +1,6 @@
//! The AST pointer.
//!
//! Provides `P<T>`, a frozen owned smart pointer.
//! Provides [`P<T>`][struct@P], an owned smart pointer.
//!
//! # Motivations and benefits
//!
@ -8,18 +8,14 @@
//! passes (e.g., one may be able to bypass the borrow checker with a shared
//! `ExprKind::AddrOf` node taking a mutable borrow).
//!
//! * **Immutability**: `P<T>` disallows mutating its inner `T`, unlike `Box<T>`
//! (unless it contains an `Unsafe` interior, but that may be denied later).
//! This mainly prevents mistakes, but also enforces a kind of "purity".
//!
//! * **Efficiency**: folding can reuse allocation space for `P<T>` and `Vec<T>`,
//! the latter even when the input and output types differ (as it would be the
//! case with arenas or a GADT AST using type parameters to toggle features).
//!
//! * **Maintainability**: `P<T>` provides a fixed interface - `Deref`,
//! `and_then` and `map` - which can remain fully functional even if the
//! implementation changes (using a special thread-local heap, for example).
//! Moreover, a switch to, e.g., `P<'a, T>` would be easy and mostly automated.
//! * **Maintainability**: `P<T>` provides an interface, which can remain fully
//! functional even if the implementation changes (using a special thread-local
//! heap, for example). Moreover, a switch to, e.g., `P<'a, T>` would be easy
//! and mostly automated.
use std::fmt::{self, Debug, Display};
use std::ops::{Deref, DerefMut};
@ -29,6 +25,8 @@ use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
/// An owned smart pointer.
///
/// See the [module level documentation][crate::ptr] for details.
pub struct P<T: ?Sized> {
ptr: Box<T>,
}