lang: Strengthen RFC 3391 guarantees to match T-lang consensus · rust-lang/rust@7baf066 (original) (raw)
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/*!
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The guarantees in RFC 3391 were strengthened as a result of the 2024 Oct 09 T-lang meeting^1
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following the precedent of T-lang's guaranteeing^2 ABI compatibility for "Option-like" enums^2.
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We now guarantee ABI compatibility for enums that conform to these rules described by scottmcm:
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- The enum
Ehas exactly two variants.
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- One variant has exactly one field, of type
T.
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Tis arustc_nonnull_optimization_guaranteedtype.
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- All fields of the other variant are 1-ZSTs.
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Where "all" fields includes "there aren't any fields, so they're vacuously all 1-ZSTs".
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Note: "1-ZST" means a type of size 0 and alignment 1.
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The reason alignment of the zero-sized type matters is it can affect the alignment of the enum,
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which also will affect its size if the enum has a non-zero size.
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*/
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`#![allow(dead_code)]
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`#![deny(improper_ctypes)]
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`#![feature(ptr_internals)]
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`@@ -59,4 +82,52 @@ extern "C" {
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`fn result_1zst_exhaustive_no_field_e(x: Result<NoField, num::NonZero>);
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`}
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// Custom "Result-like" enum for testing custom "Option-like" types are also accepted
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enum Either<L, R> {
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Left(L),
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Right(R),
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}
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extern "C" {
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fn either_ref_t(x: Either<&'static u8, ()>);
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fn either_fn_t(x: Either<extern "C" fn(), ()>);
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fn either_nonnull_t(x: Either<std::ptr::NonNull, ()>);
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fn either_unique_t(x: Either<std::ptr::Unique, ()>);
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fn either_nonzero_u8_t(x: Either<num::NonZero, ()>);
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fn either_nonzero_u16_t(x: Either<num::NonZero, ()>);
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fn either_nonzero_u32_t(x: Either<num::NonZero, ()>);
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fn either_nonzero_u64_t(x: Either<num::NonZero, ()>);
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fn either_nonzero_usize_t(x: Either<num::NonZero, ()>);
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fn either_nonzero_i8_t(x: Either<num::NonZero, ()>);
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fn either_nonzero_i16_t(x: Either<num::NonZero, ()>);
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fn either_nonzero_i32_t(x: Either<num::NonZero, ()>);
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fn either_nonzero_i64_t(x: Either<num::NonZero, ()>);
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fn either_nonzero_isize_t(x: Either<num::NonZero, ()>);
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fn either_transparent_struct_t(x: Either<TransparentStruct<num::NonZero>, ()>);
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fn either_transparent_enum_t(x: Either<TransparentEnum<num::NonZero>, ()>);
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fn either_phantom_t(x: Either<num::NonZero, std:📑:PhantomData<()>>);
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fn either_1zst_exhaustive_no_variant_t(x: Either<num::NonZero, Z>);
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fn either_1zst_exhaustive_no_field_t(x: Either<num::NonZero, NoField>);
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fn either_ref_e(x: Either<(), &'static u8>);
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fn either_fn_e(x: Either<(), extern "C" fn()>);
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fn either_nonnull_e(x: Either<(), std::ptr::NonNull>);
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fn either_unique_e(x: Either<(), std::ptr::Unique>);
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fn either_nonzero_u8_e(x: Either<(), num::NonZero>);
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fn either_nonzero_u16_e(x: Either<(), num::NonZero>);
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fn either_nonzero_u32_e(x: Either<(), num::NonZero>);
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fn either_nonzero_u64_e(x: Either<(), num::NonZero>);
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fn either_nonzero_usize_e(x: Either<(), num::NonZero>);
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fn either_nonzero_i8_e(x: Either<(), num::NonZero>);
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fn either_nonzero_i16_e(x: Either<(), num::NonZero>);
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fn either_nonzero_i32_e(x: Either<(), num::NonZero>);
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fn either_nonzero_i64_e(x: Either<(), num::NonZero>);
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fn either_nonzero_isize_e(x: Either<(), num::NonZero>);
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fn either_transparent_struct_e(x: Either<(), TransparentStruct<num::NonZero>>);
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fn either_transparent_enum_e(x: Either<(), TransparentEnum<num::NonZero>>);
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fn either_phantom_e(x: Either<num::NonZero, std:📑:PhantomData<()>>);
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fn either_1zst_exhaustive_no_variant_e(x: Either<Z, num::NonZero>);
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fn either_1zst_exhaustive_no_field_e(x: Either<NoField, num::NonZero>);
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}
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`pub fn main() {}
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