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Make Copy unsafe to implement for ADTs with unsafe fields

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As a rule, the application of `unsafe` to a declaration requires that use-sites
of that declaration also require `unsafe`. For example, a field declared
`unsafe` may only be read in the lexical context of an `unsafe` block.

For nearly all safe traits, the safety obligations of fields are explicitly
discharged when they are mentioned in method definitions. For example,
idiomatically implementing `Clone` (a safe trait) for a type with unsafe fields
will require `unsafe` to clone those fields.

Prior to this commit, `Copy` violated this rule. The trait is marked safe, and
although it has no explicit methods, its implementation permits reads of `Self`.

This commit resolves this by making `Copy` conditionally safe to implement. It
remains safe to implement for ADTs without unsafe fields, but unsafe to
implement for ADTs with unsafe fields.

Tracking: #132922
This commit is contained in:
Jack Wrenn 2024-12-06 17:11:36 +00:00
parent 9c707a8b76
commit 3ce35a4ec5
12 changed files with 164 additions and 52 deletions
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34
compiler/rustc_codegen_gcc/example/mini_core.rs
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@ -52,24 +52,24 @@ impl<T: ?Sized> LegacyReceiver for &mut T {}
impl<T: ?Sized, A: Allocator> LegacyReceiver for Box<T, A> {}
#[lang = "copy"]
pub unsafe trait Copy {}
pub trait Copy {}
unsafe impl Copy for bool {}
unsafe impl Copy for u8 {}
unsafe impl Copy for u16 {}
unsafe impl Copy for u32 {}
unsafe impl Copy for u64 {}
unsafe impl Copy for usize {}
unsafe impl Copy for i8 {}
unsafe impl Copy for i16 {}
unsafe impl Copy for i32 {}
unsafe impl Copy for isize {}
unsafe impl Copy for f32 {}
unsafe impl Copy for f64 {}
unsafe impl Copy for char {}
unsafe impl<'a, T: ?Sized> Copy for &'a T {}
unsafe impl<T: ?Sized> Copy for *const T {}
unsafe impl<T: ?Sized> Copy for *mut T {}
impl Copy for bool {}
impl Copy for u8 {}
impl Copy for u16 {}
impl Copy for u32 {}
impl Copy for u64 {}
impl Copy for usize {}
impl Copy for i8 {}
impl Copy for i16 {}
impl Copy for i32 {}
impl Copy for isize {}
impl Copy for f32 {}
impl Copy for f64 {}
impl Copy for char {}
impl<'a, T: ?Sized> Copy for &'a T {}
impl<T: ?Sized> Copy for *const T {}
impl<T: ?Sized> Copy for *mut T {}
#[lang = "sync"]
pub unsafe trait Sync {}