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Rollup merge of #125021 - joshlf:patch-11, r=RalfJung

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Update reference safety requirements

Per https://github.com/rust-lang/rust/pull/116677#issuecomment-1945495786, the language as written promises too much. This PR relaxes the language to be consistent with current semantics. If and when #117945 is implemented, we can revert to the old language.

While we're here, we also require that references be non-null.

cc ``@RalfJung``
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Guillaume Gomez 2024-05-12 13:41:57 +02:00 • committed by GitHub
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library/core/src/primitive_docs.rs
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@ -1467,8 +1467,9 @@ mod prim_usize {}
/// For all types, `T: ?Sized`, and for all `t: &T` or `t: &mut T`, when such values cross an API
/// boundary, the following invariants must generally be upheld:
///
/// * `t` is non-null
/// * `t` is aligned to `align_of_val(t)`
/// * `t` is dereferenceable for `size_of_val(t)` many bytes
/// * if `size_of_val(t) > 0`, then `t` is dereferenceable for `size_of_val(t)` many bytes
///
/// If `t` points at address `a`, being "dereferenceable" for N bytes means that the memory range
/// `[a, a + N)` is all contained within a single [allocated object].