3aa14e3b2e
In its first step of computing transmutability, `rustc_transmutability` constructs a byte-level representation of type layout (`Tree`). Previously, this representation was computed for ADTs by inspecting the ADT definition and performing our own layout computations. This process was error-prone, verbose, and limited our ability to analyze many types (particularly default-repr types). In this PR, we instead construct `Tree`s from `rustc_target::abi::Layout`s. This helps ensure that layout optimizations are reflected our analyses, and increases the kinds of types we can now analyze, including: - default repr ADTs - transparent unions - `UnsafeCell`-containing types Overall, this PR expands the expressvity of `rustc_transmutability` to be much closer to the transmutability analysis performed by miri. Future PRs will work to close the remaining gaps (e.g., support for `Box`, raw pointers, `NonZero*`, coroutines, etc.).
72 lines
2.2 KiB
Rust
72 lines
2.2 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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mod assert {
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use std::mem::{Assume, BikeshedIntrinsicFrom};
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pub fn is_maybe_transmutable<Src, Dst>()
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where
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Dst: BikeshedIntrinsicFrom<Src, {
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Assume {
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alignment: true,
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lifetimes: true,
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safety: true,
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validity: true,
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}
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}>
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{}
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}
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fn void() {
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enum Void {}
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// This transmutation is vacuously acceptable; since one cannot construct a
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// `Void`, unsoundness cannot directly arise from transmuting a void into
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// anything else.
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assert::is_maybe_transmutable::<Void, u128>();
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assert::is_maybe_transmutable::<(), Void>(); //~ ERROR: cannot be safely transmuted
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}
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// Non-ZST uninhabited types are, nonetheless, uninhabited.
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fn yawning_void() {
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enum Void {}
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struct YawningVoid(Void, u128);
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const _: () = {
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assert!(std::mem::size_of::<YawningVoid>() == std::mem::size_of::<u128>());
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// Just to be sure the above constant actually evaluated:
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assert!(false); //~ ERROR: evaluation of constant value failed
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};
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// This transmutation is vacuously acceptable; since one cannot construct a
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// `Void`, unsoundness cannot directly arise from transmuting a void into
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// anything else.
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assert::is_maybe_transmutable::<YawningVoid, u128>();
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assert::is_maybe_transmutable::<(), Void>(); //~ ERROR: cannot be safely transmuted
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}
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// References to uninhabited types are, logically, uninhabited, but for layout
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// purposes are not ZSTs, and aren't treated as uninhabited when they appear in
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// enum variants.
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fn distant_void() {
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enum Void {}
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enum DistantVoid {
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A(&'static Void)
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}
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const _: () = {
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assert!(std::mem::size_of::<DistantVoid>() == std::mem::size_of::<usize>());
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// Just to be sure the above constant actually evaluated:
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assert!(false); //~ ERROR: evaluation of constant value failed
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};
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assert::is_maybe_transmutable::<DistantVoid, ()>();
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assert::is_maybe_transmutable::<DistantVoid, &'static Void>();
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assert::is_maybe_transmutable::<u128, DistantVoid>(); //~ ERROR: cannot be safely transmuted
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}
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