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fix(macros): reject #[repr(C)] on enums in derive(Type) - #4508
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… for enums The derive took the first path-only item of #[repr(..)] as the integer type, so #[repr(C)] produced `as C` casts that don't compile. Only use integer reprs; anything else is treated like an enum without a repr.
Collaborator
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Did you see this comment on a prior PR I reviewed: #4403 (comment) |
repr(C) doesn't say whether the enum should be encoded as a string or as a C-like integer, and the C integer type differs per target. Instead of guessing, emit a compile error that points at #[repr(i32)] or removing the repr. Integer reprs work as before (also combined with C, e.g. #[repr(C, u8)]). Layout-only reprs like align(..), packed, transparent and Rust are still ignored since they don't affect the encoding.
thelastbackspace
changed the title
#[repr(C)] and other non-integer reprs in derive(Type) for enums#[repr(C)] on enums in derive(Type)
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Yes, I saw it, thanks for the pointer. I changed this PR to reject |
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Does your PR solve an issue?
fixes #4366
The enum derive picked the first path-only item in
#[repr(..)]as the integer type to encode through. With#[repr(C)]that ended up asC, so the expansion hadMyEnum::A as Cand failed with confusing errors.Following the review on #4403,
#[repr(C)]on an enum is now rejected with a clear error instead of guessing what it should map to:Other details:
u8..u128,i8..i128,usize,isize) are used as the encoded type.#[repr(C, u8)]is allowed since the integer type is explicit there.align(..),packed,transparentandRustare still ignored. They only affect layout and don't say anything about the encoding, so I didn't want to error on them.I added unit tests in
sqlx-macros-core/src/derives/attributes.rs(enum_repr_c_is_rejected,enum_repr_c_with_integer_is_accepted,enum_layout_only_reprs_are_ignored). The first two fail without the change. I also checked the error end to end on a sqlite derive.Is this a breaking change?
No. Enums with only
#[repr(C)]didn't compile before either, now they just get a better error.