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uses_power_alignment: wording tweaks

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Ralf Jung
2025-03-28 13:40:53 +01:00
parent e77a8f439c
commit 0ce025175d
1 changed files with 8 additions and 6 deletions
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compiler/rustc_lint/src/types.rs
+8 -6
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@@ -756,10 +756,10 @@ fn diag_item_cmpop(diag_item: Symbol) -> Option<ComparisonOp> {
/// *subsequent* fields of the associated structs to use an alignment value
/// where the floating-point type is aligned on a 4-byte boundary.
///
/// The power alignment rule for structs needed for C compatibility is
/// unimplementable within `repr(C)` in the compiler without building in
/// handling of references to packed fields and infectious nested layouts,
/// so a warning is produced in these situations.
/// Effectively, subsequent floating-point fields act as-if they are `repr(packed(4))`. This
/// would be unsound to do in a `repr(C)` type without all the restrictions that come with
/// `repr(packed)`. Rust instead chooses a layout that maintains soundness of Rust code, at the
/// expense of incompatibility with C code.
///
/// ### Example
///
@@ -791,8 +791,10 @@ fn diag_item_cmpop(diag_item: Symbol) -> Option<ComparisonOp> {
/// - offset_of!(Floats, a) == 0
/// - offset_of!(Floats, b) == 8
/// - offset_of!(Floats, c) == 12
/// However, rust currently aligns `c` at offset_of!(Floats, c) == 16.
/// Thus, a warning should be produced for the above struct in this case.
///
/// However, Rust currently aligns `c` at `offset_of!(Floats, c) == 16`.
/// Using offset 12 would be unsound since `f64` generally must be 8-aligned on this target.
/// Thus, a warning is produced for the above struct.
USES_POWER_ALIGNMENT,
Warn,
"Structs do not follow the power alignment rule under repr(C)"