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Commit | Line | Data |
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5e7ed085 FG |
1 | //! Least upper bound. See [`lattice`]. |
2 | ||
c34b1796 | 3 | use super::combine::CombineFields; |
c34b1796 | 4 | use super::lattice::{self, LatticeDir}; |
dfeec247 | 5 | use super::InferCtxt; |
c34b1796 | 6 | use super::Subtype; |
1a4d82fc | 7 | |
f9f354fc | 8 | use crate::infer::combine::ConstEquateRelation; |
5e7ed085 | 9 | use crate::traits::{ObligationCause, PredicateObligation}; |
ba9703b0 XL |
10 | use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation}; |
11 | use rustc_middle::ty::{self, Ty, TyCtxt}; | |
1a4d82fc JJ |
12 | |
13 | /// "Least upper bound" (common supertype) | |
dc9dc135 XL |
14 | pub struct Lub<'combine, 'infcx, 'tcx> { |
15 | fields: &'combine mut CombineFields<'infcx, 'tcx>, | |
5bcae85e | 16 | a_is_expected: bool, |
1a4d82fc JJ |
17 | } |
18 | ||
dc9dc135 XL |
19 | impl<'combine, 'infcx, 'tcx> Lub<'combine, 'infcx, 'tcx> { |
20 | pub fn new( | |
21 | fields: &'combine mut CombineFields<'infcx, 'tcx>, | |
22 | a_is_expected: bool, | |
23 | ) -> Lub<'combine, 'infcx, 'tcx> { | |
74b04a01 | 24 | Lub { fields, a_is_expected } |
54a0048b | 25 | } |
c34b1796 | 26 | } |
1a4d82fc | 27 | |
a2a8927a | 28 | impl<'tcx> TypeRelation<'tcx> for Lub<'_, '_, 'tcx> { |
dfeec247 XL |
29 | fn tag(&self) -> &'static str { |
30 | "Lub" | |
31 | } | |
1a4d82fc | 32 | |
487cf647 FG |
33 | fn intercrate(&self) -> bool { |
34 | assert!(!self.fields.infcx.intercrate); | |
35 | false | |
36 | } | |
37 | ||
dfeec247 XL |
38 | fn tcx(&self) -> TyCtxt<'tcx> { |
39 | self.fields.tcx() | |
40 | } | |
1a4d82fc | 41 | |
dfeec247 XL |
42 | fn param_env(&self) -> ty::ParamEnv<'tcx> { |
43 | self.fields.param_env | |
44 | } | |
416331ca | 45 | |
dfeec247 XL |
46 | fn a_is_expected(&self) -> bool { |
47 | self.a_is_expected | |
48 | } | |
1a4d82fc | 49 | |
487cf647 FG |
50 | fn mark_ambiguous(&mut self) { |
51 | bug!("mark_ambiguous used outside of coherence"); | |
52 | } | |
53 | ||
dfeec247 XL |
54 | fn relate_with_variance<T: Relate<'tcx>>( |
55 | &mut self, | |
56 | variance: ty::Variance, | |
17df50a5 | 57 | _info: ty::VarianceDiagInfo<'tcx>, |
f035d41b XL |
58 | a: T, |
59 | b: T, | |
dfeec247 | 60 | ) -> RelateResult<'tcx, T> { |
c34b1796 | 61 | match variance { |
5bcae85e | 62 | ty::Invariant => self.fields.equate(self.a_is_expected).relate(a, b), |
c34b1796 | 63 | ty::Covariant => self.relate(a, b), |
cc61c64b | 64 | // FIXME(#41044) -- not correct, need test |
1b1a35ee | 65 | ty::Bivariant => Ok(a), |
5bcae85e | 66 | ty::Contravariant => self.fields.glb(self.a_is_expected).relate(a, b), |
1a4d82fc JJ |
67 | } |
68 | } | |
69 | ||
c34b1796 AL |
70 | fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { |
71 | lattice::super_lattice_tys(self, a, b) | |
1a4d82fc JJ |
72 | } |
73 | ||
dfeec247 XL |
74 | fn regions( |
75 | &mut self, | |
76 | a: ty::Region<'tcx>, | |
77 | b: ty::Region<'tcx>, | |
78 | ) -> RelateResult<'tcx, ty::Region<'tcx>> { | |
79 | debug!("{}.regions({:?}, {:?})", self.tag(), a, b); | |
1a4d82fc | 80 | |
94222f64 | 81 | let origin = Subtype(Box::new(self.fields.trace.clone())); |
74b04a01 XL |
82 | Ok(self.fields.infcx.inner.borrow_mut().unwrap_region_constraints().lub_regions( |
83 | self.tcx(), | |
84 | origin, | |
85 | a, | |
86 | b, | |
87 | )) | |
1a4d82fc JJ |
88 | } |
89 | ||
48663c56 XL |
90 | fn consts( |
91 | &mut self, | |
5099ac24 FG |
92 | a: ty::Const<'tcx>, |
93 | b: ty::Const<'tcx>, | |
94 | ) -> RelateResult<'tcx, ty::Const<'tcx>> { | |
48663c56 XL |
95 | self.fields.infcx.super_combine_consts(self, a, b) |
96 | } | |
97 | ||
dfeec247 XL |
98 | fn binders<T>( |
99 | &mut self, | |
cdc7bbd5 XL |
100 | a: ty::Binder<'tcx, T>, |
101 | b: ty::Binder<'tcx, T>, | |
102 | ) -> RelateResult<'tcx, ty::Binder<'tcx, T>> | |
dfeec247 XL |
103 | where |
104 | T: Relate<'tcx>, | |
c34b1796 | 105 | { |
9c376795 FG |
106 | // LUB of a binder and itself is just itself |
107 | if a == b { | |
108 | return Ok(a); | |
109 | } | |
110 | ||
abe05a73 | 111 | debug!("binders(a={:?}, b={:?})", a, b); |
923072b8 FG |
112 | if a.skip_binder().has_escaping_bound_vars() || b.skip_binder().has_escaping_bound_vars() { |
113 | // When higher-ranked types are involved, computing the LUB is | |
114 | // very challenging, switch to invariance. This is obviously | |
115 | // overly conservative but works ok in practice. | |
116 | self.relate_with_variance( | |
117 | ty::Variance::Invariant, | |
118 | ty::VarianceDiagInfo::default(), | |
119 | a, | |
120 | b, | |
121 | )?; | |
122 | Ok(a) | |
123 | } else { | |
124 | Ok(ty::Binder::dummy(self.relate(a.skip_binder(), b.skip_binder())?)) | |
125 | } | |
1a4d82fc | 126 | } |
c34b1796 | 127 | } |
1a4d82fc | 128 | |
f9f354fc | 129 | impl<'tcx> ConstEquateRelation<'tcx> for Lub<'_, '_, 'tcx> { |
5099ac24 | 130 | fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>) { |
f9f354fc XL |
131 | self.fields.add_const_equate_obligation(self.a_is_expected, a, b); |
132 | } | |
133 | } | |
134 | ||
dc9dc135 | 135 | impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Lub<'combine, 'infcx, 'tcx> { |
2b03887a | 136 | fn infcx(&self) -> &'infcx InferCtxt<'tcx> { |
c34b1796 AL |
137 | self.fields.infcx |
138 | } | |
139 | ||
476ff2be SL |
140 | fn cause(&self) -> &ObligationCause<'tcx> { |
141 | &self.fields.trace.cause | |
142 | } | |
143 | ||
5e7ed085 FG |
144 | fn add_obligations(&mut self, obligations: Vec<PredicateObligation<'tcx>>) { |
145 | self.fields.obligations.extend(obligations) | |
146 | } | |
147 | ||
5bcae85e SL |
148 | fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> { |
149 | let mut sub = self.fields.sub(self.a_is_expected); | |
f035d41b XL |
150 | sub.relate(a, v)?; |
151 | sub.relate(b, v)?; | |
c34b1796 | 152 | Ok(()) |
1a4d82fc | 153 | } |
5e7ed085 FG |
154 | |
155 | fn define_opaque_types(&self) -> bool { | |
156 | self.fields.define_opaque_types | |
157 | } | |
1a4d82fc | 158 | } |