diff options
| -rw-r--r-- | compiler/rustc_lint/src/types.rs | 14 |
1 files changed, 8 insertions, 6 deletions
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs index 7109fefbe78..d98b439ba89 100644 --- a/compiler/rustc_lint/src/types.rs +++ b/compiler/rustc_lint/src/types.rs @@ -756,10 +756,10 @@ declare_lint! { /// *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 @@ declare_lint! { /// - 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)" |