e9eae28eee
Previously, `rustc_transmute`'s layout representations were genericized over `R`, a reference. Now, it's instead genericized over representations of type and region. This allows us to move reference transmutability logic from `rustc_trait_selection` to `rustc_transmutability` (and thus unit test it independently of the compiler), and — in a follow-up PR — will make it possible to support analyzing function pointer transmutability with minimal surgery.
48 lines
2.0 KiB
Rust
48 lines
2.0 KiB
Rust
#![crate_type = "lib"]
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#![feature(transmutability)]
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#![allow(dead_code, incomplete_features, non_camel_case_types)]
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use std::cell::UnsafeCell;
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mod assert {
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use std::mem::{Assume, TransmuteFrom};
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pub fn is_maybe_transmutable<Src, Dst>()
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where
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Dst: TransmuteFrom<Src, { Assume::SAFETY }>
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{}
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}
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fn value_to_value() {
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// We accept value-to-value transmutations of `UnsafeCell`-containing types,
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// because owning a value implies exclusive access.
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assert::is_maybe_transmutable::<UnsafeCell<u8>, u8>();
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assert::is_maybe_transmutable::<u8, UnsafeCell<u8>>();
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assert::is_maybe_transmutable::<UnsafeCell<u8>, UnsafeCell<u8>>();
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}
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fn ref_to_ref() {
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// We forbid `UnsafeCell`-containing ref-to-ref transmutations, because the
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// two types may use different, incompatible synchronization strategies.
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assert::is_maybe_transmutable::<&'static u8, &'static UnsafeCell<u8>>(); //~ ERROR: cannot be safely transmuted
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assert::is_maybe_transmutable::<&'static UnsafeCell<u8>, &'static UnsafeCell<u8>>(); //~ ERROR: cannot be safely transmuted
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}
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fn mut_to_mut() {
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// `UnsafeCell` does't matter for `&mut T` to `&mut U`, since exclusive
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// borrows can't be used for shared access.
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assert::is_maybe_transmutable::<&'static mut u8, &'static mut UnsafeCell<u8>>();
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assert::is_maybe_transmutable::<&'static mut UnsafeCell<u8>, &'static mut u8>();
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assert::is_maybe_transmutable::<&'static mut UnsafeCell<u8>, &'static mut UnsafeCell<u8>>();
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}
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fn mut_to_ref() {
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// `&mut UnsafeCell` is irrelevant in the source.
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assert::is_maybe_transmutable::<&'static mut UnsafeCell<bool>, &'static u8>();
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// `&UnsafeCell` in forbidden in the destination, since the destination can be used to
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// invalidate a shadowed source reference.
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assert::is_maybe_transmutable::<&'static mut bool, &'static UnsafeCell<u8>>(); //~ ERROR: cannot be safely transmuted
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assert::is_maybe_transmutable::<&'static mut UnsafeCell<bool>, &'static UnsafeCell<u8>>(); //~ ERROR: cannot be safely transmuted
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}
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