1 use super::combine::CombineFields;
2 use super::lattice::{self, LatticeDir};
6 use crate::traits::ObligationCause;
7 use rustc::ty::relate::{Relate, RelateResult, TypeRelation};
8 use rustc::ty::{self, Ty, TyCtxt};
10 /// "Least upper bound" (common supertype)
11 pub struct Lub<'combine, 'infcx, 'tcx> {
12 fields: &'combine mut CombineFields<'infcx, 'tcx>,
16 impl<'combine, 'infcx, 'tcx> Lub<'combine, 'infcx, 'tcx> {
18 fields: &'combine mut CombineFields<'infcx, 'tcx>,
20 ) -> Lub<'combine, 'infcx, 'tcx> {
21 Lub { fields, a_is_expected }
25 impl TypeRelation<'tcx> for Lub<'combine, 'infcx, 'tcx> {
26 fn tag(&self) -> &'static str {
30 fn tcx(&self) -> TyCtxt<'tcx> {
34 fn param_env(&self) -> ty::ParamEnv<'tcx> {
38 fn a_is_expected(&self) -> bool {
42 fn relate_with_variance<T: Relate<'tcx>>(
44 variance: ty::Variance,
47 ) -> RelateResult<'tcx, T> {
49 ty::Invariant => self.fields.equate(self.a_is_expected).relate(a, b),
50 ty::Covariant => self.relate(a, b),
51 // FIXME(#41044) -- not correct, need test
52 ty::Bivariant => Ok(a.clone()),
53 ty::Contravariant => self.fields.glb(self.a_is_expected).relate(a, b),
57 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
58 lattice::super_lattice_tys(self, a, b)
65 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
66 debug!("{}.regions({:?}, {:?})", self.tag(), a, b);
68 let origin = Subtype(box self.fields.trace.clone());
69 Ok(self.fields.infcx.inner.borrow_mut().unwrap_region_constraints().lub_regions(
79 a: &'tcx ty::Const<'tcx>,
80 b: &'tcx ty::Const<'tcx>,
81 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
82 self.fields.infcx.super_combine_consts(self, a, b)
89 ) -> RelateResult<'tcx, ty::Binder<T>>
93 debug!("binders(a={:?}, b={:?})", a, b);
95 // When higher-ranked types are involved, computing the LUB is
96 // very challenging, switch to invariance. This is obviously
97 // overly conservative but works ok in practice.
98 self.relate_with_variance(ty::Variance::Invariant, a, b)?;
103 impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Lub<'combine, 'infcx, 'tcx> {
104 fn infcx(&self) -> &'infcx InferCtxt<'infcx, 'tcx> {
108 fn cause(&self) -> &ObligationCause<'tcx> {
109 &self.fields.trace.cause
112 fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> {
113 let mut sub = self.fields.sub(self.a_is_expected);