bjoernager/rust
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do not implement unsafe auto traits for types with unsafe fields

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If a type has unsafe fields, its safety invariants are not simply
the conjunction of its field types' safety invariants. Consequently,
it's invalid to reason about the safety properties of these types
in a purely structural manner — i.e., the manner in which `auto`
traits are implemented.

Makes progress towards #132922.
This commit is contained in:
Jack Wrenn 2024-12-05 20:15:08 +00:00
parent 0e98766a54
commit a122dde217
16 changed files with 95 additions and 0 deletions
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9
compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
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@ -18,6 +18,7 @@ use rustc_infer::traits::{
use rustc_middle::ty::fast_reject::DeepRejectCtxt;
use rustc_middle::ty::{self, ToPolyTraitRef, Ty, TypeVisitableExt, TypingMode};
use rustc_middle::{bug, span_bug};
use rustc_type_ir::Interner;
use tracing::{debug, instrument, trace};
use super::SelectionCandidate::*;
@ -794,6 +795,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
| ty::Never
| ty::Tuple(_)
| ty::CoroutineWitness(..) => {
use rustc_type_ir::inherent::*;
// Only consider auto impls of unsafe traits when there are
// no unsafe fields.
if self.tcx().trait_is_unsafe(def_id) && self_ty.has_unsafe_fields() {
return;
}
// Only consider auto impls if there are no manual impls for the root of `self_ty`.
//
// For example, we only consider auto candidates for `&i32: Auto` if no explicit impl