use super::assembly::{self, Candidate, CandidateSource};
use super::infcx_ext::InferCtxtExt;
-use super::{Certainty, EvalCtxt, Goal, QueryResult};
+use super::{CanonicalResponse, Certainty, EvalCtxt, Goal, QueryResult};
use rustc_hir::def_id::DefId;
use rustc_infer::infer::InferCtxt;
use rustc_infer::traits::query::NoSolution;
+use rustc_infer::traits::util::supertraits;
use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
use rustc_middle::ty::{TraitPredicate, TypeVisitable};
)
}
- fn consider_builtin_pointer_sized_candidate(
+ fn consider_builtin_pointer_like_candidate(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
) -> QueryResult<'tcx> {
.to_predicate(tcx),
)
}
+
+ fn consider_builtin_unsize_candidate(
+ ecx: &mut EvalCtxt<'_, 'tcx>,
+ goal: Goal<'tcx, Self>,
+ ) -> QueryResult<'tcx> {
+ let tcx = ecx.tcx();
+ let a_ty = goal.predicate.self_ty();
+ let b_ty = goal.predicate.trait_ref.substs.type_at(1);
+ if b_ty.is_ty_var() {
+ return ecx.make_canonical_response(Certainty::AMBIGUOUS);
+ }
+ ecx.infcx.probe(|_| {
+ match (a_ty.kind(), b_ty.kind()) {
+ // Trait upcasting, or `dyn Trait + Auto + 'a` -> `dyn Trait + 'b`
+ (&ty::Dynamic(_, _, ty::Dyn), &ty::Dynamic(_, _, ty::Dyn)) => {
+ // Dyn upcasting is handled separately, since due to upcasting,
+ // when there are two supertraits that differ by substs, we
+ // may return more than one query response.
+ return Err(NoSolution);
+ }
+ // `T` -> `dyn Trait` unsizing
+ (_, &ty::Dynamic(data, region, ty::Dyn)) => {
+ // Can only unsize to an object-safe type
+ if data
+ .principal_def_id()
+ .map_or(false, |def_id| !tcx.check_is_object_safe(def_id))
+ {
+ return Err(NoSolution);
+ }
+
+ let Some(sized_def_id) = tcx.lang_items().sized_trait() else {
+ return Err(NoSolution);
+ };
+ let nested_goals: Vec<_> = data
+ .iter()
+ // Check that the type implements all of the predicates of the def-id.
+ // (i.e. the principal, all of the associated types match, and any auto traits)
+ .map(|pred| goal.with(tcx, pred.with_self_ty(tcx, a_ty)))
+ .chain([
+ // The type must be Sized to be unsized.
+ goal.with(
+ tcx,
+ ty::Binder::dummy(tcx.mk_trait_ref(sized_def_id, [a_ty])),
+ ),
+ // The type must outlive the lifetime of the `dyn` we're unsizing into.
+ goal.with(tcx, ty::Binder::dummy(ty::OutlivesPredicate(a_ty, region))),
+ ])
+ .collect();
+
+ ecx.evaluate_all_and_make_canonical_response(nested_goals)
+ }
+ // `[T; n]` -> `[T]` unsizing
+ (&ty::Array(a_elem_ty, ..), &ty::Slice(b_elem_ty)) => {
+ // We just require that the element type stays the same
+ let nested_goals = ecx.infcx.eq(goal.param_env, a_elem_ty, b_elem_ty)?;
+ ecx.evaluate_all_and_make_canonical_response(nested_goals)
+ }
+ // Struct unsizing `Struct<T>` -> `Struct<U>` where `T: Unsize<U>`
+ (&ty::Adt(a_def, a_substs), &ty::Adt(b_def, b_substs))
+ if a_def.is_struct() && a_def.did() == b_def.did() =>
+ {
+ let unsizing_params = tcx.unsizing_params_for_adt(a_def.did());
+ // We must be unsizing some type parameters. This also implies
+ // that the struct has a tail field.
+ if unsizing_params.is_empty() {
+ return Err(NoSolution);
+ }
+
+ let tail_field = a_def
+ .non_enum_variant()
+ .fields
+ .last()
+ .expect("expected unsized ADT to have a tail field");
+ let tail_field_ty = tcx.bound_type_of(tail_field.did);
+
+ let a_tail_ty = tail_field_ty.subst(tcx, a_substs);
+ let b_tail_ty = tail_field_ty.subst(tcx, b_substs);
+
+ // Substitute just the unsizing params from B into A. The type after
+ // this substitution must be equal to B. This is so we don't unsize
+ // unrelated type parameters.
+ let new_a_substs = tcx.mk_substs(a_substs.iter().enumerate().map(|(i, a)| {
+ if unsizing_params.contains(i as u32) { b_substs[i] } else { a }
+ }));
+ let unsized_a_ty = tcx.mk_adt(a_def, new_a_substs);
+
+ // Finally, we require that `TailA: Unsize<TailB>` for the tail field
+ // types.
+ let mut nested_goals = ecx.infcx.eq(goal.param_env, unsized_a_ty, b_ty)?;
+ nested_goals.push(goal.with(
+ tcx,
+ ty::Binder::dummy(
+ tcx.mk_trait_ref(goal.predicate.def_id(), [a_tail_ty, b_tail_ty]),
+ ),
+ ));
+
+ ecx.evaluate_all_and_make_canonical_response(nested_goals)
+ }
+ // Tuple unsizing `(.., T)` -> `(.., U)` where `T: Unsize<U>`
+ (&ty::Tuple(a_tys), &ty::Tuple(b_tys))
+ if a_tys.len() == b_tys.len() && !a_tys.is_empty() =>
+ {
+ let (a_last_ty, a_rest_tys) = a_tys.split_last().unwrap();
+ let b_last_ty = b_tys.last().unwrap();
+
+ // Substitute just the tail field of B., and require that they're equal.
+ let unsized_a_ty = tcx.mk_tup(a_rest_tys.iter().chain([b_last_ty]));
+ let mut nested_goals = ecx.infcx.eq(goal.param_env, unsized_a_ty, b_ty)?;
+
+ // Similar to ADTs, require that the rest of the fields are equal.
+ nested_goals.push(goal.with(
+ tcx,
+ ty::Binder::dummy(
+ tcx.mk_trait_ref(goal.predicate.def_id(), [*a_last_ty, *b_last_ty]),
+ ),
+ ));
+
+ ecx.evaluate_all_and_make_canonical_response(nested_goals)
+ }
+ _ => Err(NoSolution),
+ }
+ })
+ }
+
+ fn consider_builtin_dyn_upcast_candidates(
+ ecx: &mut EvalCtxt<'_, 'tcx>,
+ goal: Goal<'tcx, Self>,
+ ) -> Vec<CanonicalResponse<'tcx>> {
+ let tcx = ecx.tcx();
+
+ let a_ty = goal.predicate.self_ty();
+ let b_ty = goal.predicate.trait_ref.substs.type_at(1);
+ let ty::Dynamic(a_data, a_region, ty::Dyn) = *a_ty.kind() else {
+ return vec![];
+ };
+ let ty::Dynamic(b_data, b_region, ty::Dyn) = *b_ty.kind() else {
+ return vec![];
+ };
+
+ // All of a's auto traits need to be in b's auto traits.
+ let auto_traits_compatible =
+ b_data.auto_traits().all(|b| a_data.auto_traits().any(|a| a == b));
+ if !auto_traits_compatible {
+ return vec![];
+ }
+
+ let mut unsize_dyn_to_principal = |principal: Option<ty::PolyExistentialTraitRef<'tcx>>| {
+ ecx.infcx.probe(|_| -> Result<_, NoSolution> {
+ // Require that all of the trait predicates from A match B, except for
+ // the auto traits. We do this by constructing a new A type with B's
+ // auto traits, and equating these types.
+ let new_a_data = principal
+ .into_iter()
+ .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait))
+ .chain(a_data.iter().filter(|a| {
+ matches!(a.skip_binder(), ty::ExistentialPredicate::Projection(_))
+ }))
+ .chain(
+ b_data
+ .auto_traits()
+ .map(ty::ExistentialPredicate::AutoTrait)
+ .map(ty::Binder::dummy),
+ );
+ let new_a_data = tcx.mk_poly_existential_predicates(new_a_data);
+ let new_a_ty = tcx.mk_dynamic(new_a_data, b_region, ty::Dyn);
+
+ // We also require that A's lifetime outlives B's lifetime.
+ let mut nested_obligations = ecx.infcx.eq(goal.param_env, new_a_ty, b_ty)?;
+ nested_obligations.push(
+ goal.with(tcx, ty::Binder::dummy(ty::OutlivesPredicate(a_region, b_region))),
+ );
+
+ ecx.evaluate_all_and_make_canonical_response(nested_obligations)
+ })
+ };
+
+ let mut responses = vec![];
+ // If the principal def ids match (or are both none), then we're not doing
+ // trait upcasting. We're just removing auto traits (or shortening the lifetime).
+ if a_data.principal_def_id() == b_data.principal_def_id() {
+ if let Ok(response) = unsize_dyn_to_principal(a_data.principal()) {
+ responses.push(response);
+ }
+ } else if let Some(a_principal) = a_data.principal()
+ && let Some(b_principal) = b_data.principal()
+ {
+ for super_trait_ref in supertraits(tcx, a_principal.with_self_ty(tcx, a_ty)) {
+ if super_trait_ref.def_id() != b_principal.def_id() {
+ continue;
+ }
+ let erased_trait_ref = super_trait_ref
+ .map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
+ if let Ok(response) = unsize_dyn_to_principal(Some(erased_trait_ref)) {
+ responses.push(response);
+ }
+ }
+ }
+
+ responses
+ }
+
+ fn consider_builtin_discriminant_kind_candidate(
+ ecx: &mut EvalCtxt<'_, 'tcx>,
+ _goal: Goal<'tcx, Self>,
+ ) -> QueryResult<'tcx> {
+ // `DiscriminantKind` is automatically implemented for every type.
+ ecx.make_canonical_response(Certainty::Yes)
+ }
}
impl<'tcx> EvalCtxt<'_, 'tcx> {
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