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Extend BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE.

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To temporarily allow a `str` field in a packed struct using `derive`,
along with `[u8]`.
This commit is contained in:
Nicholas Nethercote 2023-02-06 12:58:39 +11:00
parent ef934d9b63
commit a70d03b624
4 changed files with 81 additions and 25 deletions
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55
compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
View file

@ -1557,31 +1557,46 @@ impl<'a> TraitDef<'a> {
}),
),
);
// In general, fields in packed structs are copied via a
// block, e.g. `&{self.0}`. The one exception is `[u8]`
// fields, which cannot be copied and also never cause
// unaligned references. This exception is allowed to
// handle the `FlexZeroSlice` type in the `zerovec` crate
// within `icu4x-0.9.0`.
//
// Once use of `icu4x-0.9.0` has dropped sufficiently, this
// exception should be removed.
let is_u8_slice = if let TyKind::Slice(ty) = &struct_field.ty.kind &&
let TyKind::Path(None, rustc_ast::Path { segments, .. }) = &ty.kind &&
let [seg] = segments.as_slice() &&
seg.ident.name == sym::u8 && seg.args.is_none()
{
true
} else {
false
};
if is_packed {
if is_u8_slice {
// In general, fields in packed structs are copied via a
// block, e.g. `&{self.0}`. The two exceptions are `[u8]`
// and `str` fields, which cannot be copied and also never
// cause unaligned references. These exceptions are allowed
// to handle the `FlexZeroSlice` type in the `zerovec`
// crate within `icu4x-0.9.0`.
//
// Once use of `icu4x-0.9.0` has dropped sufficiently, this
// exception should be removed.
let is_simple_path = |ty: &P<ast::Ty>, sym| {
if let TyKind::Path(None, ast::Path { segments, .. }) = &ty.kind &&
let [seg] = segments.as_slice() &&
seg.ident.name == sym && seg.args.is_none()
{
true
} else {
false
}
};
let exception = if let TyKind::Slice(ty) = &struct_field.ty.kind &&
is_simple_path(ty, sym::u8)
{
Some("byte")
} else if is_simple_path(&struct_field.ty, sym::str) {
Some("string")
} else {
None
};
if let Some(ty) = exception {
cx.sess.parse_sess.buffer_lint_with_diagnostic(
BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE,
sp,
ast::CRATE_NODE_ID,
"byte slice in a packed struct that derives a built-in trait",
&format!(
"{} slice in a packed struct that derives a built-in trait",
ty
),
rustc_lint_defs::BuiltinLintDiagnostics::ByteSliceInPackedStructWithDerive
);
} else {