1 use super::combine::CombineFields;
3 use super::lattice::{self, LatticeDir};
6 use crate::traits::ObligationCause;
7 use crate::ty::{self, Ty, TyCtxt};
8 use crate::ty::relate::{Relate, RelateResult, TypeRelation};
10 /// "Least upper bound" (common supertype)
11 pub struct Lub<'combine, 'infcx: 'combine, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> {
12 fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>,
16 impl<'combine, 'infcx, 'gcx, 'tcx> Lub<'combine, 'infcx, 'gcx, 'tcx> {
17 pub fn new(fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>, a_is_expected: bool)
18 -> Lub<'combine, 'infcx, 'gcx, 'tcx>
20 Lub { fields: fields, a_is_expected: a_is_expected }
24 impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
25 for Lub<'combine, 'infcx, 'gcx, 'tcx>
27 fn tag(&self) -> &'static str { "Lub" }
29 fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> { self.fields.tcx() }
31 fn a_is_expected(&self) -> bool { self.a_is_expected }
33 fn relate_with_variance<T: Relate<'tcx>>(&mut self,
34 variance: ty::Variance,
37 -> RelateResult<'tcx, T>
40 ty::Invariant => self.fields.equate(self.a_is_expected).relate(a, b),
41 ty::Covariant => self.relate(a, b),
42 // FIXME(#41044) -- not correct, need test
43 ty::Bivariant => Ok(a.clone()),
44 ty::Contravariant => self.fields.glb(self.a_is_expected).relate(a, b),
48 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
49 lattice::super_lattice_tys(self, a, b)
52 fn regions(&mut self, a: ty::Region<'tcx>, b: ty::Region<'tcx>)
53 -> RelateResult<'tcx, ty::Region<'tcx>> {
54 debug!("{}.regions({:?}, {:?})",
59 let origin = Subtype(self.fields.trace.clone());
60 Ok(self.fields.infcx.borrow_region_constraints().lub_regions(self.tcx(), origin, a, b))
65 a: &'tcx ty::Const<'tcx>,
66 b: &'tcx ty::Const<'tcx>,
67 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
68 debug!("{}.consts({:?}, {:?})", self.tag(), a, b);
73 self.fields.infcx.super_combine_consts(self, a, b)
76 fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
77 -> RelateResult<'tcx, ty::Binder<T>>
80 debug!("binders(a={:?}, b={:?})", a, b);
82 // When higher-ranked types are involved, computing the LUB is
83 // very challenging, switch to invariance. This is obviously
84 // overly conservative but works ok in practice.
85 self.relate_with_variance(ty::Variance::Invariant, a, b)?;
90 impl<'combine, 'infcx, 'gcx, 'tcx> LatticeDir<'infcx, 'gcx, 'tcx>
91 for Lub<'combine, 'infcx, 'gcx, 'tcx>
93 fn infcx(&self) -> &'infcx InferCtxt<'infcx, 'gcx, 'tcx> {
97 fn cause(&self) -> &ObligationCause<'tcx> {
98 &self.fields.trace.cause
101 fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> {
102 let mut sub = self.fields.sub(self.a_is_expected);