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 intercrate(&self) -> bool {
  36         self.fields.infcx.intercrate
  37     }
  38
  39     fn param_env(&self) -> ty::ParamEnv<'tcx> {
  40         self.fields.param_env
  41     }
  42
  43     fn a_is_expected(&self) -> bool {
  44         self.a_is_expected
  45     }
  46
  47     fn mark_ambiguous(&mut self) {
  48         self.fields.mark_ambiguous();
  49     }
  50
  51     fn relate_item_substs(
  52         &mut self,
  53         _item_def_id: DefId,
  54         a_subst: SubstsRef<'tcx>,
  55         b_subst: SubstsRef<'tcx>,
  56     ) -> RelateResult<'tcx, SubstsRef<'tcx>> {
  57         // N.B., once we are equating types, we don't care about
  58         // variance, so don't try to lookup the variance here. This
  59         // also avoids some cycles (e.g., #41849) since looking up
  60         // variance requires computing types which can require
  61         // performing trait matching (which then performs equality
  62         // unification).
  63
  64         relate::relate_substs(self, a_subst, b_subst)
  65     }
  66
  67     fn relate_with_variance<T: Relate<'tcx>>(
  68         &mut self,
  69         _: ty::Variance,
  70         _info: ty::VarianceDiagInfo<'tcx>,
  71         a: T,
  72         b: T,
  73     ) -> RelateResult<'tcx, T> {
  74         self.relate(a, b)
  75     }
  76
  77     #[instrument(skip(self), level = "debug")]
  78     fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
  79         if a == b {
  80             return Ok(a);
  81         }
  82
  83         trace!(a = ?a.kind(), b = ?b.kind());
  84
  85         let infcx = self.fields.infcx;
  86
  87         let a = infcx.inner.borrow_mut().type_variables().replace_if_possible(a);
  88         let b = infcx.inner.borrow_mut().type_variables().replace_if_possible(b);
  89
  90         match (a.kind(), b.kind()) {
  91             (&ty::Infer(TyVar(a_id)), &ty::Infer(TyVar(b_id))) => {
  92                 infcx.inner.borrow_mut().type_variables().equate(a_id, b_id);
  93             }
  94
  95             (&ty::Infer(TyVar(a_id)), _) => {
  96                 self.fields.instantiate(b, RelationDir::EqTo, a_id, self.a_is_expected)?;
  97             }
  98
  99             (_, &ty::Infer(TyVar(b_id))) => {
 100                 self.fields.instantiate(a, RelationDir::EqTo, b_id, self.a_is_expected)?;
 101             }
 102
 103             (&ty::Opaque(a_def_id, _), &ty::Opaque(b_def_id, _)) if a_def_id == b_def_id => {
 104                 self.fields.infcx.super_combine_tys(self, a, b)?;
 105             }
 106             (&ty::Opaque(did, ..), _) | (_, &ty::Opaque(did, ..))
 107                 if self.fields.define_opaque_types && did.is_local() =>
 108             {
 109                 self.fields.obligations.extend(
 110                     infcx
 111                         .handle_opaque_type(
 112                             a,
 113                             b,
 114                             self.a_is_expected(),
 115                             &self.fields.trace.cause,
 116                             self.param_env(),
 117                         )?
 118                         .obligations,
 119                 );
 120             }
 121             // Optimization of GeneratorWitness relation since we know that all
 122             // free regions are replaced with bound regions during construction.
 123             // This greatly speeds up equating of GeneratorWitness.
 124             (&ty::GeneratorWitness(a_types), &ty::GeneratorWitness(b_types)) => {
 125                 let a_types = infcx.tcx.anonymize_bound_vars(a_types);
 126                 let b_types = infcx.tcx.anonymize_bound_vars(b_types);
 127                 if a_types.bound_vars() == b_types.bound_vars() {
 128                     let (a_types, b_types) = infcx.replace_bound_vars_with_placeholders(
 129                         a_types.map_bound(|a_types| (a_types, b_types.skip_binder())),
 130                     );
 131                     for (a, b) in std::iter::zip(a_types, b_types) {
 132                         self.relate(a, b)?;
 133                     }
 134                 } else {
 135                     return Err(ty::error::TypeError::Sorts(ty::relate::expected_found(
 136                         self, a, b,
 137                     )));
 138                 }
 139             }
 140
 141             _ => {
 142                 self.fields.infcx.super_combine_tys(self, a, b)?;
 143             }
 144         }
 145
 146         Ok(a)
 147     }
 148
 149     fn regions(
 150         &mut self,
 151         a: ty::Region<'tcx>,
 152         b: ty::Region<'tcx>,
 153     ) -> RelateResult<'tcx, ty::Region<'tcx>> {
 154         debug!("{}.regions({:?}, {:?})", self.tag(), a, b);
 155         let origin = Subtype(Box::new(self.fields.trace.clone()));
 156         self.fields
 157             .infcx
 158             .inner
 159             .borrow_mut()
 160             .unwrap_region_constraints()
 161             .make_eqregion(origin, a, b);
 162         Ok(a)
 163     }
 164
 165     fn consts(
 166         &mut self,
 167         a: ty::Const<'tcx>,
 168         b: ty::Const<'tcx>,
 169     ) -> RelateResult<'tcx, ty::Const<'tcx>> {
 170         self.fields.infcx.super_combine_consts(self, a, b)
 171     }
 172
 173     fn binders<T>(
 174         &mut self,
 175         a: ty::Binder<'tcx, T>,
 176         b: ty::Binder<'tcx, T>,
 177     ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
 178     where
 179         T: Relate<'tcx>,
 180     {
 181         if a.skip_binder().has_escaping_bound_vars() || b.skip_binder().has_escaping_bound_vars() {
 182             self.fields.higher_ranked_sub(a, b, self.a_is_expected)?;
 183             self.fields.higher_ranked_sub(b, a, self.a_is_expected)?;
 184         } else {
 185             // Fast path for the common case.
 186             self.relate(a.skip_binder(), b.skip_binder())?;
 187         }
 188         Ok(a)
 189     }
 190 }
 191
 192 impl<'tcx> ConstEquateRelation<'tcx> for Equate<'_, '_, 'tcx> {
 193     fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>) {
 194         self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
 195     }
 196 }