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[rustc.git] / compiler / rustc_infer / src / infer / equate.rs
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f9f354fc 1use super::combine::{CombineFields, ConstEquateRelation, RelationDir};
48663c56 2use super::Subtype;
cc61c64b 3
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4use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
5use rustc_middle::ty::subst::SubstsRef;
6use rustc_middle::ty::TyVar;
7use rustc_middle::ty::{self, Ty, TyCtxt};
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8
9use rustc_hir::def_id::DefId;
1a4d82fc 10
b039eaaf 11/// Ensures `a` is made equal to `b`. Returns `a` on success.
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12pub struct Equate<'combine, 'infcx, 'tcx> {
13 fields: &'combine mut CombineFields<'infcx, 'tcx>,
5bcae85e 14 a_is_expected: bool,
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15}
16
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17impl<'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> {
74b04a01 22 Equate { fields, a_is_expected }
54a0048b 23 }
c34b1796 24}
1a4d82fc 25
a2a8927a 26impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
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27 fn tag(&self) -> &'static str {
28 "Equate"
29 }
1a4d82fc 30
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31 fn tcx(&self) -> TyCtxt<'tcx> {
32 self.fields.tcx()
33 }
1a4d82fc 34
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35 fn param_env(&self) -> ty::ParamEnv<'tcx> {
36 self.fields.param_env
37 }
416331ca 38
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39 fn a_is_expected(&self) -> bool {
40 self.a_is_expected
41 }
1a4d82fc 42
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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>> {
0731742a 49 // N.B., once we are equating types, we don't care about
cc61c64b 50 // variance, so don't try to lookup the variance here. This
0731742a 51 // also avoids some cycles (e.g., #41849) since looking up
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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
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59 fn relate_with_variance<T: Relate<'tcx>>(
60 &mut self,
61 _: ty::Variance,
17df50a5 62 _info: ty::VarianceDiagInfo<'tcx>,
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63 a: T,
64 b: T,
dfeec247 65 ) -> RelateResult<'tcx, T> {
c34b1796 66 self.relate(a, b)
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67 }
68
c34b1796 69 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
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70 debug!("{}.tys({:?}, {:?})", self.tag(), a, b);
71 if a == b {
72 return Ok(a);
73 }
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74
75 let infcx = self.fields.infcx;
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76 let a = infcx.inner.borrow_mut().type_variables().replace_if_possible(a);
77 let b = infcx.inner.borrow_mut().type_variables().replace_if_possible(b);
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78
79 debug!("{}.tys: replacements ({:?}, {:?})", self.tag(), a, b);
80
1b1a35ee 81 match (a.kind(), b.kind()) {
b7449926 82 (&ty::Infer(TyVar(a_id)), &ty::Infer(TyVar(b_id))) => {
f9f354fc 83 infcx.inner.borrow_mut().type_variables().equate(a_id, b_id);
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84 }
85
b7449926 86 (&ty::Infer(TyVar(a_id)), _) => {
cc61c64b 87 self.fields.instantiate(b, RelationDir::EqTo, a_id, self.a_is_expected)?;
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88 }
89
b7449926 90 (_, &ty::Infer(TyVar(b_id))) => {
cc61c64b 91 self.fields.instantiate(a, RelationDir::EqTo, b_id, self.a_is_expected)?;
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92 }
93
94 _ => {
a7813a04 95 self.fields.infcx.super_combine_tys(self, a, b)?;
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96 }
97 }
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98
99 Ok(a)
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100 }
101
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102 fn regions(
103 &mut self,
104 a: ty::Region<'tcx>,
105 b: ty::Region<'tcx>,
106 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
107 debug!("{}.regions({:?}, {:?})", self.tag(), a, b);
94222f64 108 let origin = Subtype(Box::new(self.fields.trace.clone()));
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109 self.fields
110 .infcx
111 .inner
112 .borrow_mut()
113 .unwrap_region_constraints()
114 .make_eqregion(origin, a, b);
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115 Ok(a)
116 }
117
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118 fn consts(
119 &mut self,
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120 a: ty::Const<'tcx>,
121 b: ty::Const<'tcx>,
122 ) -> RelateResult<'tcx, ty::Const<'tcx>> {
e1599b0c 123 self.fields.infcx.super_combine_consts(self, a, b)
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124 }
125
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126 fn binders<T>(
127 &mut self,
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128 a: ty::Binder<'tcx, T>,
129 b: ty::Binder<'tcx, T>,
130 ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
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131 where
132 T: Relate<'tcx>,
1a4d82fc 133 {
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134 if a.skip_binder().has_escaping_bound_vars() || b.skip_binder().has_escaping_bound_vars() {
135 self.fields.higher_ranked_sub(a, b, self.a_is_expected)?;
136 self.fields.higher_ranked_sub(b, a, self.a_is_expected)
137 } else {
138 // Fast path for the common case.
139 self.relate(a.skip_binder(), b.skip_binder())?;
f035d41b 140 Ok(a)
74b04a01 141 }
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142 }
143}
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144
145impl<'tcx> ConstEquateRelation<'tcx> for Equate<'_, '_, 'tcx> {
5099ac24 146 fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>) {
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147 self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
148 }
149}