346397d081
Rename `pointer` field on `Pin` A few days ago, I was helping another user create a self-referential type using `PhantomPinned`. However, I noticed an odd behavior when I tried to access one of the type's fields via `Pin`'s `Deref` impl: ```rust use std::{marker::PhantomPinned, ptr}; struct Pinned { data: i32, pointer: *const i32, _pin: PhantomPinned, } fn main() { let mut b = Box::pin(Pinned { data: 42, pointer: ptr::null(), _pin: PhantomPinned, }); { let pinned = unsafe { b.as_mut().get_unchecked_mut() }; pinned.pointer = &pinned.data; } println!("{}", unsafe { *b.pointer }); } ``` ```rust error[E0658]: use of unstable library feature 'unsafe_pin_internals' --> <source>:19:30 | 19 | println!("{}", unsafe { *b.pointer }); | ^^^^^^^^^ error[E0277]: `Pinned` doesn't implement `std::fmt::Display` --> <source>:19:20 | 19 | println!("{}", unsafe { *b.pointer }); | ^^^^^^^^^^^^^^^^^^^^^ `Pinned` cannot be formatted with the default formatter | = help: the trait `std::fmt::Display` is not implemented for `Pinned` = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info) ``` Since the user named their field `pointer`, it conflicts with the `pointer` field on `Pin`, which is public but unstable since Rust 1.60.0 with #93176. On versions from 1.33.0 to 1.59.0, where the field on `Pin` is private, this program compiles and prints `42` as expected. To avoid this confusing behavior, this PR renames `pointer` to `__pointer`, so that it's less likely to conflict with a `pointer` field on the underlying type, as accessed through the `Deref` impl. This is technically a breaking change for anyone who names their field `__pointer` on the inner type; if this is undesirable, it could be renamed to something more longwinded. It's also a nightly breaking change for any external users of `unsafe_pin_internals`. |
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The Rust Programming Language
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