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-rw-r--r--compiler/rustc_infer/src/infer/relate/equate.rs188
1 files changed, 188 insertions, 0 deletions
diff --git a/compiler/rustc_infer/src/infer/relate/equate.rs b/compiler/rustc_infer/src/infer/relate/equate.rs
new file mode 100644
index 000000000..cb62f2583
--- /dev/null
+++ b/compiler/rustc_infer/src/infer/relate/equate.rs
@@ -0,0 +1,188 @@
+use super::combine::{CombineFields, ObligationEmittingRelation};
+use crate::infer::{DefineOpaqueTypes, SubregionOrigin};
+use crate::traits::PredicateObligations;
+
+use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
+use rustc_middle::ty::GenericArgsRef;
+use rustc_middle::ty::TyVar;
+use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
+
+use rustc_hir::def_id::DefId;
+
+/// Ensures `a` is made equal to `b`. Returns `a` on success.
+pub struct Equate<'combine, 'infcx, 'tcx> {
+ fields: &'combine mut CombineFields<'infcx, 'tcx>,
+ a_is_expected: bool,
+}
+
+impl<'combine, 'infcx, 'tcx> Equate<'combine, 'infcx, 'tcx> {
+ pub fn new(
+ fields: &'combine mut CombineFields<'infcx, 'tcx>,
+ a_is_expected: bool,
+ ) -> Equate<'combine, 'infcx, 'tcx> {
+ Equate { fields, a_is_expected }
+ }
+}
+
+impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
+ fn tag(&self) -> &'static str {
+ "Equate"
+ }
+
+ fn tcx(&self) -> TyCtxt<'tcx> {
+ self.fields.tcx()
+ }
+
+ fn a_is_expected(&self) -> bool {
+ self.a_is_expected
+ }
+
+ fn relate_item_args(
+ &mut self,
+ _item_def_id: DefId,
+ a_arg: GenericArgsRef<'tcx>,
+ b_arg: GenericArgsRef<'tcx>,
+ ) -> RelateResult<'tcx, GenericArgsRef<'tcx>> {
+ // N.B., once we are equating types, we don't care about
+ // variance, so don't try to lookup the variance here. This
+ // also avoids some cycles (e.g., #41849) since looking up
+ // variance requires computing types which can require
+ // performing trait matching (which then performs equality
+ // unification).
+
+ relate::relate_args_invariantly(self, a_arg, b_arg)
+ }
+
+ fn relate_with_variance<T: Relate<'tcx>>(
+ &mut self,
+ _: ty::Variance,
+ _info: ty::VarianceDiagInfo<'tcx>,
+ a: T,
+ b: T,
+ ) -> RelateResult<'tcx, T> {
+ self.relate(a, b)
+ }
+
+ #[instrument(skip(self), level = "debug")]
+ fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
+ if a == b {
+ return Ok(a);
+ }
+
+ trace!(a = ?a.kind(), b = ?b.kind());
+
+ let infcx = self.fields.infcx;
+
+ let a = infcx.inner.borrow_mut().type_variables().replace_if_possible(a);
+ let b = infcx.inner.borrow_mut().type_variables().replace_if_possible(b);
+
+ match (a.kind(), b.kind()) {
+ (&ty::Infer(TyVar(a_id)), &ty::Infer(TyVar(b_id))) => {
+ infcx.inner.borrow_mut().type_variables().equate(a_id, b_id);
+ }
+
+ (&ty::Infer(TyVar(a_id)), _) => {
+ self.fields.instantiate(b, ty::Invariant, a_id, self.a_is_expected)?;
+ }
+
+ (_, &ty::Infer(TyVar(b_id))) => {
+ self.fields.instantiate(a, ty::Invariant, b_id, self.a_is_expected)?;
+ }
+
+ (
+ &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, .. }),
+ &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }),
+ ) if a_def_id == b_def_id => {
+ self.fields.infcx.super_combine_tys(self, a, b)?;
+ }
+ (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }), _)
+ | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }))
+ if self.fields.define_opaque_types == DefineOpaqueTypes::Yes
+ && def_id.is_local()
+ && !self.fields.infcx.next_trait_solver() =>
+ {
+ self.fields.obligations.extend(
+ infcx
+ .handle_opaque_type(
+ a,
+ b,
+ self.a_is_expected(),
+ &self.fields.trace.cause,
+ self.param_env(),
+ )?
+ .obligations,
+ );
+ }
+ _ => {
+ self.fields.infcx.super_combine_tys(self, a, b)?;
+ }
+ }
+
+ Ok(a)
+ }
+
+ fn regions(
+ &mut self,
+ a: ty::Region<'tcx>,
+ b: ty::Region<'tcx>,
+ ) -> RelateResult<'tcx, ty::Region<'tcx>> {
+ debug!("{}.regions({:?}, {:?})", self.tag(), a, b);
+ let origin = SubregionOrigin::Subtype(Box::new(self.fields.trace.clone()));
+ self.fields
+ .infcx
+ .inner
+ .borrow_mut()
+ .unwrap_region_constraints()
+ .make_eqregion(origin, a, b);
+ Ok(a)
+ }
+
+ fn consts(
+ &mut self,
+ a: ty::Const<'tcx>,
+ b: ty::Const<'tcx>,
+ ) -> RelateResult<'tcx, ty::Const<'tcx>> {
+ self.fields.infcx.super_combine_consts(self, a, b)
+ }
+
+ fn binders<T>(
+ &mut self,
+ a: ty::Binder<'tcx, T>,
+ b: ty::Binder<'tcx, T>,
+ ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
+ where
+ T: Relate<'tcx>,
+ {
+ // A binder is equal to itself if it's structurally equal to itself
+ if a == b {
+ return Ok(a);
+ }
+
+ if a.skip_binder().has_escaping_bound_vars() || b.skip_binder().has_escaping_bound_vars() {
+ self.fields.higher_ranked_sub(a, b, self.a_is_expected)?;
+ self.fields.higher_ranked_sub(b, a, self.a_is_expected)?;
+ } else {
+ // Fast path for the common case.
+ self.relate(a.skip_binder(), b.skip_binder())?;
+ }
+ Ok(a)
+ }
+}
+
+impl<'tcx> ObligationEmittingRelation<'tcx> for Equate<'_, '_, 'tcx> {
+ fn param_env(&self) -> ty::ParamEnv<'tcx> {
+ self.fields.param_env
+ }
+
+ fn register_predicates(&mut self, obligations: impl IntoIterator<Item: ty::ToPredicate<'tcx>>) {
+ self.fields.register_predicates(obligations);
+ }
+
+ fn register_obligations(&mut self, obligations: PredicateObligations<'tcx>) {
+ self.fields.register_obligations(obligations);
+ }
+
+ fn alias_relate_direction(&self) -> ty::AliasRelationDirection {
+ ty::AliasRelationDirection::Equate
+ }
+}