src/librustc/infer/equate.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use super::combine::{CombineFields, RelationDir};
  12 use super::{Subtype};
  13
  14 use hir::def_id::DefId;
  15
  16 use ty::{self, Ty, TyCtxt};
  17 use ty::TyVar;
  18 use ty::subst::Substs;
  19 use ty::relate::{self, Relate, RelateResult, TypeRelation};
  20
  21 /// Ensures `a` is made equal to `b`. Returns `a` on success.
  22 pub struct Equate<'combine, 'infcx: 'combine, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> {
  23     fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>,
  24     a_is_expected: bool,
  25 }
  26
  27 impl<'combine, 'infcx, 'gcx, 'tcx> Equate<'combine, 'infcx, 'gcx, 'tcx> {
  28     pub fn new(fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>, a_is_expected: bool)
  29         -> Equate<'combine, 'infcx, 'gcx, 'tcx>
  30     {
  31         Equate { fields: fields, a_is_expected: a_is_expected }
  32     }
  33 }
  34
  35 impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
  36     for Equate<'combine, 'infcx, 'gcx, 'tcx>
  37 {
  38     fn tag(&self) -> &'static str { "Equate" }
  39
  40     fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> { self.fields.tcx() }
  41
  42     fn a_is_expected(&self) -> bool { self.a_is_expected }
  43
  44     fn relate_item_substs(&mut self,
  45                           _item_def_id: DefId,
  46                           a_subst: &'tcx Substs<'tcx>,
  47                           b_subst: &'tcx Substs<'tcx>)
  48                           -> RelateResult<'tcx, &'tcx Substs<'tcx>>
  49     {
  50         // NB: Once we are equating types, we don't care about
  51         // variance, so don't try to lookup the variance here. This
  52         // also avoids some cycles (e.g. #41849) since looking up
  53         // variance requires computing types which can require
  54         // performing trait matching (which then performs equality
  55         // unification).
  56
  57         relate::relate_substs(self, None, a_subst, b_subst)
  58     }
  59
  60     fn relate_with_variance<T: Relate<'tcx>>(&mut self,
  61                                              _: ty::Variance,
  62                                              a: &T,
  63                                              b: &T)
  64                                              -> RelateResult<'tcx, T>
  65     {
  66         self.relate(a, b)
  67     }
  68
  69     fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
  70         debug!("{}.tys({:?}, {:?})", self.tag(),
  71                a, b);
  72         if a == b { return Ok(a); }
  73
  74         let infcx = self.fields.infcx;
  75         let a = infcx.type_variables.borrow_mut().replace_if_possible(a);
  76         let b = infcx.type_variables.borrow_mut().replace_if_possible(b);
  77         match (&a.sty, &b.sty) {
  78             (&ty::TyInfer(TyVar(a_id)), &ty::TyInfer(TyVar(b_id))) => {
  79                 infcx.type_variables.borrow_mut().equate(a_id, b_id);
  80                 Ok(a)
  81             }
  82
  83             (&ty::TyInfer(TyVar(a_id)), _) => {
  84                 self.fields.instantiate(b, RelationDir::EqTo, a_id, self.a_is_expected)?;
  85                 Ok(a)
  86             }
  87
  88             (_, &ty::TyInfer(TyVar(b_id))) => {
  89                 self.fields.instantiate(a, RelationDir::EqTo, b_id, self.a_is_expected)?;
  90                 Ok(a)
  91             }
  92
  93             _ => {
  94                 self.fields.infcx.super_combine_tys(self, a, b)?;
  95                 Ok(a)
  96             }
  97         }
  98     }
  99
 100     fn regions(&mut self, a: ty::Region<'tcx>, b: ty::Region<'tcx>)
 101                -> RelateResult<'tcx, ty::Region<'tcx>> {
 102         debug!("{}.regions({:?}, {:?})",
 103                self.tag(),
 104                a,
 105                b);
 106         let origin = Subtype(self.fields.trace.clone());
 107         self.fields.infcx.region_vars.make_eqregion(origin, a, b);
 108         Ok(a)
 109     }
 110
 111     fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
 112                   -> RelateResult<'tcx, ty::Binder<T>>
 113         where T: Relate<'tcx>
 114     {
 115         self.fields.higher_ranked_sub(a, b, self.a_is_expected)?;
 116         self.fields.higher_ranked_sub(b, a, self.a_is_expected)
 117     }
 118 }