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Auto merge of #115524 - RalfJung:misalign, r=wesleywiser

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const-eval: make misalignment a hard error

It's been a future-incompat error (showing up in cargo's reports) since https://github.com/rust-lang/rust/pull/104616, Rust 1.68, released in March.  That should be long enough.

The question for the lang team is simply -- should we move ahead with this, making const-eval alignment failures a hard error? (It turns out some of them accidentally already were hard errors since #104616. But not all so this is still a breaking change. Crater found no regression.)
This commit is contained in:
bors 2023-10-14 00:57:09 +00:00
commit 75a5dd05bc
12 changed files with 114 additions and 193 deletions
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40
compiler/rustc_lint_defs/src/builtin.rs
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@ -986,45 +986,6 @@ declare_lint! {
"detects trivial casts of numeric types which could be removed"
}
declare_lint! {
/// The `invalid_alignment` lint detects dereferences of misaligned pointers during
/// constant evaluation.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![feature(const_mut_refs)]
/// const FOO: () = unsafe {
/// let x = &[0_u8; 4];
/// let y = x.as_ptr().cast::<u32>();
/// let mut z = 123;
/// y.copy_to_nonoverlapping(&mut z, 1); // the address of a `u8` array is unknown
/// // and thus we don't know if it is aligned enough for copying a `u32`.
/// };
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The compiler allowed dereferencing raw pointers irrespective of alignment
/// during const eval due to the const evaluator at the time not making it easy
/// or cheap to check. Now that it is both, this is not accepted anymore.
///
/// Since it was undefined behaviour to begin with, this breakage does not violate
/// Rust's stability guarantees. Using undefined behaviour can cause arbitrary
/// behaviour, including failure to build.
///
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub INVALID_ALIGNMENT,
Deny,
"raw pointers must be aligned before dereferencing",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
reference: "issue #68585 <https://github.com/rust-lang/rust/issues/104616>",
};
}
declare_lint! {
/// The `exported_private_dependencies` lint detects private dependencies
/// that are exposed in a public interface.
@ -3430,7 +3391,6 @@ declare_lint_pass! {
INDIRECT_STRUCTURAL_MATCH,
INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
INLINE_NO_SANITIZE,
INVALID_ALIGNMENT,
INVALID_DOC_ATTRIBUTES,
INVALID_MACRO_EXPORT_ARGUMENTS,
INVALID_TYPE_PARAM_DEFAULT,