compiler/rustc_infer/src/infer/equate.rs

   1 use super::combine::{CombineFields, ConstEquateRelation, RelationDir};
   2 use super::Subtype;
   3
   4 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
   5 use rustc_middle::ty::subst::SubstsRef;
   6 use rustc_middle::ty::TyVar;
   7 use rustc_middle::ty::{self, Ty, TyCtxt};
   8
   9 use rustc_hir::def_id::DefId;
  10
  11 /// Ensures `a` is made equal to `b`. Returns `a` on success.
  12 pub struct Equate<'combine, 'infcx, 'tcx> {
  13     fields: &'combine mut CombineFields<'infcx, 'tcx>,
  14     a_is_expected: bool,
  15 }
  16
  17 impl<'combine, 'infcx, 'tcx> Equate<'combine, 'infcx, 'tcx> {
  18     pub fn new(
  19         fields: &'combine mut CombineFields<'infcx, 'tcx>,
  20         a_is_expected: bool,
  21     ) -> Equate<'combine, 'infcx, 'tcx> {
  22         Equate { fields, a_is_expected }
  23     }
  24 }
  25
  26 impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
  27     fn tag(&self) -> &'static str {
  28         "Equate"
  29     }
  30
  31     fn tcx(&self) -> TyCtxt<'tcx> {
  32         self.fields.tcx()
  33     }
  34
  35     fn param_env(&self) -> ty::ParamEnv<'tcx> {
  36         self.fields.param_env
  37     }
  38
  39     fn a_is_expected(&self) -> bool {
  40         self.a_is_expected
  41     }
  42
  43     fn relate_item_substs(
  44         &mut self,
  45         _item_def_id: DefId,
  46         a_subst: SubstsRef<'tcx>,
  47         b_subst: SubstsRef<'tcx>,
  48     ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
  49         // N.B., once we are equating types, we don't care about
  50         // variance, so don't try to lookup the variance here. This
  51         // also avoids some cycles (e.g., #41849) since looking up
  52         // variance requires computing types which can require
  53         // performing trait matching (which then performs equality
  54         // unification).
  55
  56         relate::relate_substs(self, None, a_subst, b_subst)
  57     }
  58
  59     fn relate_with_variance<T: Relate<'tcx>>(
  60         &mut self,
  61         _: ty::Variance,
  62         _info: ty::VarianceDiagInfo<'tcx>,
  63         a: T,
  64         b: T,
  65     ) -> RelateResult<'tcx, T> {
  66         self.relate(a, b)
  67     }
  68
  69     #[instrument(skip(self), level = "debug")]
  70     fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
  71         if a == b {
  72             return Ok(a);
  73         }
  74
  75         trace!(a = ?a.kind(), b = ?b.kind());
  76
  77         let infcx = self.fields.infcx;
  78
  79         let a = infcx.inner.borrow_mut().type_variables().replace_if_possible(a);
  80         let b = infcx.inner.borrow_mut().type_variables().replace_if_possible(b);
  81
  82         match (a.kind(), b.kind()) {
  83             (&ty::Infer(TyVar(a_id)), &ty::Infer(TyVar(b_id))) => {
  84                 infcx.inner.borrow_mut().type_variables().equate(a_id, b_id);
  85             }
  86
  87             (&ty::Infer(TyVar(a_id)), _) => {
  88                 self.fields.instantiate(b, RelationDir::EqTo, a_id, self.a_is_expected)?;
  89             }
  90
  91             (_, &ty::Infer(TyVar(b_id))) => {
  92                 self.fields.instantiate(a, RelationDir::EqTo, b_id, self.a_is_expected)?;
  93             }
  94
  95             (&ty::Opaque(a_def_id, _), &ty::Opaque(b_def_id, _)) if a_def_id == b_def_id => {
  96                 self.fields.infcx.super_combine_tys(self, a, b)?;
  97             }
  98             (&ty::Opaque(did, ..), _) | (_, &ty::Opaque(did, ..))
  99                 if self.fields.define_opaque_types && did.is_local() =>
 100             {
 101                 self.fields.obligations.extend(
 102                     infcx
 103                         .handle_opaque_type(
 104                             a,
 105                             b,
 106                             self.a_is_expected(),
 107                             &self.fields.trace.cause,
 108                             self.param_env(),
 109                         )?
 110                         .obligations,
 111                 );
 112             }
 113
 114             _ => {
 115                 self.fields.infcx.super_combine_tys(self, a, b)?;
 116             }
 117         }
 118
 119         Ok(a)
 120     }
 121
 122     fn regions(
 123         &mut self,
 124         a: ty::Region<'tcx>,
 125         b: ty::Region<'tcx>,
 126     ) -> RelateResult<'tcx, ty::Region<'tcx>> {
 127         debug!("{}.regions({:?}, {:?})", self.tag(), a, b);
 128         let origin = Subtype(Box::new(self.fields.trace.clone()));
 129         self.fields
 130             .infcx
 131             .inner
 132             .borrow_mut()
 133             .unwrap_region_constraints()
 134             .make_eqregion(origin, a, b);
 135         Ok(a)
 136     }
 137
 138     fn consts(
 139         &mut self,
 140         a: ty::Const<'tcx>,
 141         b: ty::Const<'tcx>,
 142     ) -> RelateResult<'tcx, ty::Const<'tcx>> {
 143         self.fields.infcx.super_combine_consts(self, a, b)
 144     }
 145
 146     fn binders<T>(
 147         &mut self,
 148         a: ty::Binder<'tcx, T>,
 149         b: ty::Binder<'tcx, T>,
 150     ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
 151     where
 152         T: Relate<'tcx>,
 153     {
 154         if a.skip_binder().has_escaping_bound_vars() || b.skip_binder().has_escaping_bound_vars() {
 155             self.fields.higher_ranked_sub(a, b, self.a_is_expected)?;
 156             self.fields.higher_ranked_sub(b, a, self.a_is_expected)
 157         } else {
 158             // Fast path for the common case.
 159             self.relate(a.skip_binder(), b.skip_binder())?;
 160             Ok(a)
 161         }
 162     }
 163 }
 164
 165 impl<'tcx> ConstEquateRelation<'tcx> for Equate<'_, '_, 'tcx> {
 166     fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>) {
 167         self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
 168     }
 169 }