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Do not implement unsafe auto traits for types with unsafe fields #133934

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Dec 7, 2024
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4 changes: 4 additions & 0 deletions compiler/rustc_middle/src/ty/context.rs
Original file line number Diff line number Diff line change
Expand Up @@ -585,6 +585,10 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
self.trait_def(trait_def_id).implement_via_object
}

fn trait_is_unsafe(self, trait_def_id: Self::DefId) -> bool {
self.trait_def(trait_def_id).safety == hir::Safety::Unsafe
}

fn is_impl_trait_in_trait(self, def_id: DefId) -> bool {
self.is_impl_trait_in_trait(def_id)
}
Expand Down
8 changes: 8 additions & 0 deletions compiler/rustc_middle/src/ty/sty.rs
Original file line number Diff line number Diff line change
Expand Up @@ -978,6 +978,14 @@ impl<'tcx> rustc_type_ir::inherent::Ty<TyCtxt<'tcx>> for Ty<'tcx> {
fn async_destructor_ty(self, interner: TyCtxt<'tcx>) -> Ty<'tcx> {
self.async_destructor_ty(interner)
}

fn has_unsafe_fields(self) -> bool {
if let ty::Adt(adt_def, ..) = self.kind() {
adt_def.all_fields().any(|x| x.safety == hir::Safety::Unsafe)
} else {
false
}
}
}

/// Type utilities
Expand Down
8 changes: 8 additions & 0 deletions compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
Original file line number Diff line number Diff line change
Expand Up @@ -169,6 +169,14 @@ where
return result;
}

// Only consider auto impls of unsafe traits when there are no unsafe
// fields.
if ecx.cx().trait_is_unsafe(goal.predicate.def_id())
&& goal.predicate.self_ty().has_unsafe_fields()
{
return Err(NoSolution);
}

// We only look into opaque types during analysis for opaque types
// outside of their defining scope. Doing so for opaques in the
// defining scope may require calling `typeck` on the same item we're
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -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::*;
Expand Down Expand Up @@ -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
Expand Down
3 changes: 3 additions & 0 deletions compiler/rustc_type_ir/src/inherent.rs
Original file line number Diff line number Diff line change
Expand Up @@ -136,6 +136,9 @@ pub trait Ty<I: Interner<Ty = Self>>:
matches!(self.kind(), ty::FnPtr(..))
}

/// Checks whether this type is an ADT that has unsafe fields.
fn has_unsafe_fields(self) -> bool;

fn fn_sig(self, interner: I) -> ty::Binder<I, ty::FnSig<I>> {
match self.kind() {
ty::FnPtr(sig_tys, hdr) => sig_tys.with(hdr),
Expand Down
3 changes: 3 additions & 0 deletions compiler/rustc_type_ir/src/interner.rs
Original file line number Diff line number Diff line change
Expand Up @@ -270,6 +270,9 @@ pub trait Interner:

fn trait_may_be_implemented_via_object(self, trait_def_id: Self::DefId) -> bool;

/// Returns `true` if this is an `unsafe trait`.
fn trait_is_unsafe(self, trait_def_id: Self::DefId) -> bool;

fn is_impl_trait_in_trait(self, def_id: Self::DefId) -> bool;

fn delay_bug(self, msg: impl ToString) -> Self::ErrorGuaranteed;
Expand Down
17 changes: 17 additions & 0 deletions tests/ui/unsafe-fields/auto-traits.current.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,17 @@
error[E0277]: the trait bound `UnsafeEnum: UnsafeAuto` is not satisfied
--> $DIR/auto-traits.rs:24:22
|
LL | impl_unsafe_auto(UnsafeEnum::Safe(42));
| ---------------- ^^^^^^^^^^^^^^^^^^^^ the trait `UnsafeAuto` is not implemented for `UnsafeEnum`
| |
| required by a bound introduced by this call
|
note: required by a bound in `impl_unsafe_auto`
--> $DIR/auto-traits.rs:20:29
|
LL | fn impl_unsafe_auto(_: impl UnsafeAuto) {}
| ^^^^^^^^^^ required by this bound in `impl_unsafe_auto`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.
17 changes: 17 additions & 0 deletions tests/ui/unsafe-fields/auto-traits.next.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,17 @@
error[E0277]: the trait bound `UnsafeEnum: UnsafeAuto` is not satisfied
--> $DIR/auto-traits.rs:24:22
|
LL | impl_unsafe_auto(UnsafeEnum::Safe(42));
| ---------------- ^^^^^^^^^^^^^^^^^^^^ the trait `UnsafeAuto` is not implemented for `UnsafeEnum`
| |
| required by a bound introduced by this call
|
note: required by a bound in `impl_unsafe_auto`
--> $DIR/auto-traits.rs:20:29
|
LL | fn impl_unsafe_auto(_: impl UnsafeAuto) {}
| ^^^^^^^^^^ required by this bound in `impl_unsafe_auto`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.
26 changes: 26 additions & 0 deletions tests/ui/unsafe-fields/auto-traits.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,26 @@
//@ compile-flags: --crate-type=lib
//@ revisions: current next
//@[next] compile-flags: -Znext-solver

#![feature(auto_traits)]
#![feature(unsafe_fields)]
#![allow(incomplete_features)]

enum UnsafeEnum {
Safe(u8),
Unsafe { unsafe field: u8 },
}

auto trait SafeAuto {}

fn impl_safe_auto(_: impl SafeAuto) {}

unsafe auto trait UnsafeAuto {}

fn impl_unsafe_auto(_: impl UnsafeAuto) {}

fn tests() {
impl_safe_auto(UnsafeEnum::Safe(42));
impl_unsafe_auto(UnsafeEnum::Safe(42));
//~^ ERROR the trait bound `UnsafeEnum: UnsafeAuto` is not satisfied
}
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