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Remove outdated todo and clarify that slices are not ABI-compatible #214

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Merged
copybara-service merged 1 commit into from
Dec 19, 2025
+3 −11
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Remove outdated todo and clarify that slices are not ABI-compatible #214

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14 changes: 3 additions & 11 deletions cc_bindings_from_rs/generate_bindings/query_compiler.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -50,14 +50,6 @@ pub fn is_c_abi_compatible_by_value(tcx: TyCtxt<'_>, ty: Ty) -> bool {
// See `rust_builtin_type_abi_assumptions.md` for more details.
ty::TyKind::Char => true,

// TODO(b/271016831): When launching `&[T]` (not just `*const T`), consider returning
// `true` for `TyKind::Ref` and document the rationale for such decision - maybe
// something like this will be sufficient:
// - In general `TyKind::Ref` should have the same ABI as `TyKind::RawPtr`
// - References to slices (`&[T]`) or strings (`&str`) rely on assumptions
// spelled out in `rust_builtin_type_abi_assumptions.md`.
ty::TyKind::Slice { .. } => false,

// Crubit's C++ bindings for tuples, structs, and other ADTs may not preserve
// their ABI (even if they *do* preserve their memory layout). For example:
// - In System V ABI replacing a field with a fixed-length array of bytes may affect
Expand Down Expand Up @@ -89,9 +81,9 @@ pub fn is_c_abi_compatible_by_value(tcx: TyCtxt<'_>, ty: Ty) -> bool {
ty::TyKind::Array { .. } => false,
ty::TyKind::Alias { .. } => false,

// These kinds of reference-related types are not implemented yet - `is_c_abi_compatible_by_value`
// should never need to handle them, because `format_ty_for_cc` fails for such types.
ty::TyKind::Str => unimplemented!(),
// Slice references (`&[T]`, `&str`) are not guaranteed to be ABI-compatible when passed
// by-value.
ty::TyKind::Slice { .. } | ty::TyKind::Str => false,

// `format_ty_for_cc` is expected to fail for other kinds of types
// and therefore `is_c_abi_compatible_by_value` should never be called for
Expand Down