1 use super::combine::CombineFields;
2 use super::lattice::{self, LatticeDir};
6 use crate::infer::combine::ConstEquateRelation;
7 use crate::traits::ObligationCause;
8 use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation};
9 use rustc_middle::ty::{self, Ty, TyCtxt};
11 /// "Least upper bound" (common supertype)
12 pub struct Lub<'combine, 'infcx, 'tcx> {
13 fields: &'combine mut CombineFields<'infcx, 'tcx>,
17 impl<'combine, 'infcx, 'tcx> Lub<'combine, 'infcx, 'tcx> {
19 fields: &'combine mut CombineFields<'infcx, 'tcx>,
21 ) -> Lub<'combine, 'infcx, 'tcx> {
22 Lub { fields, a_is_expected }
26 impl TypeRelation<'tcx> for Lub<'combine, 'infcx, 'tcx> {
27 fn tag(&self) -> &'static str {
31 fn tcx(&self) -> TyCtxt<'tcx> {
35 fn param_env(&self) -> ty::ParamEnv<'tcx> {
39 fn a_is_expected(&self) -> bool {
43 fn relate_with_variance<T: Relate<'tcx>>(
45 variance: ty::Variance,
48 ) -> RelateResult<'tcx, T> {
50 ty::Invariant => self.fields.equate(self.a_is_expected).relate(a, b),
51 ty::Covariant => self.relate(a, b),
52 // FIXME(#41044) -- not correct, need test
53 ty::Bivariant => Ok(a.clone()),
54 ty::Contravariant => self.fields.glb(self.a_is_expected).relate(a, b),
58 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
59 lattice::super_lattice_tys(self, a, b)
66 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
67 debug!("{}.regions({:?}, {:?})", self.tag(), a, b);
69 let origin = Subtype(box self.fields.trace.clone());
70 Ok(self.fields.infcx.inner.borrow_mut().unwrap_region_constraints().lub_regions(
80 a: &'tcx ty::Const<'tcx>,
81 b: &'tcx ty::Const<'tcx>,
82 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
83 self.fields.infcx.super_combine_consts(self, a, b)
90 ) -> RelateResult<'tcx, ty::Binder<T>>
94 debug!("binders(a={:?}, b={:?})", a, b);
96 // When higher-ranked types are involved, computing the LUB is
97 // very challenging, switch to invariance. This is obviously
98 // overly conservative but works ok in practice.
99 self.relate_with_variance(ty::Variance::Invariant, a, b)?;
104 impl<'tcx> ConstEquateRelation<'tcx> for Lub<'_, '_, 'tcx> {
105 fn const_equate_obligation(&mut self, a: &'tcx ty::Const<'tcx>, b: &'tcx ty::Const<'tcx>) {
106 self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
110 impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Lub<'combine, 'infcx, 'tcx> {
111 fn infcx(&self) -> &'infcx InferCtxt<'infcx, 'tcx> {
115 fn cause(&self) -> &ObligationCause<'tcx> {
116 &self.fields.trace.cause
119 fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> {
120 let mut sub = self.fields.sub(self.a_is_expected);