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Mark ZST as FFI-safe if all its fields are PhantomData

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Modify the linting behavior and add the corresponding
regression test
This commit is contained in:
Arthur Carcano 2023-01-10 11:38:53 +01:00
parent 2b8590ef3b
commit 797f247997
2 changed files with 45 additions and 23 deletions
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46
compiler/rustc_lint/src/types.rs
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@ -878,39 +878,39 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
) -> FfiResult<'tcx> {
use FfiResult::*;
if def.repr().transparent() {
let transparent_safety = def.repr().transparent().then(|| {
// Can assume that at most one field is not a ZST, so only check
// that field's type for FFI-safety.
if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
self.check_field_type_for_ffi(cache, field, substs)
return self.check_field_type_for_ffi(cache, field, substs);
} else {
// All fields are ZSTs; this means that the type should behave
// like (), which is FFI-unsafe
// like (), which is FFI-unsafe... except if all fields are PhantomData,
// which is tested for below
FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_struct_zst, help: None }
}
} else {
// We can't completely trust repr(C) markings; make sure the fields are
// actually safe.
let mut all_phantom = !variant.fields.is_empty();
for field in &variant.fields {
match self.check_field_type_for_ffi(cache, &field, substs) {
FfiSafe => {
all_phantom = false;
}
FfiPhantom(..) if def.is_enum() => {
return FfiUnsafe {
ty,
reason: fluent::lint_improper_ctypes_enum_phantomdata,
help: None,
};
}
FfiPhantom(..) => {}
r => return r,
});
// We can't completely trust repr(C) markings; make sure the fields are
// actually safe.
let mut all_phantom = !variant.fields.is_empty();
for field in &variant.fields {
match self.check_field_type_for_ffi(cache, &field, substs) {
FfiSafe => {
all_phantom = false;
}
FfiPhantom(..) if !def.repr().transparent() && def.is_enum() => {
return FfiUnsafe {
ty,
reason: fluent::lint_improper_ctypes_enum_phantomdata,
help: None,
};
}
FfiPhantom(..) => {}
r => return transparent_safety.unwrap_or(r),
}
if all_phantom { FfiPhantom(ty) } else { FfiSafe }
}
if all_phantom { FfiPhantom(ty) } else { transparent_safety.unwrap_or(FfiSafe) }
}
/// Checks if the given type is "ffi-safe" (has a stable, well-defined