| use super::combine::CombineFields; |
| use super::InferCtxt; |
| use super::lattice::{self, LatticeDir}; |
| use super::Subtype; |
| |
| use crate::traits::ObligationCause; |
| use crate::ty::{self, Ty, TyCtxt}; |
| use crate::ty::relate::{Relate, RelateResult, TypeRelation}; |
| |
| /// "Least upper bound" (common supertype) |
| pub struct Lub<'combine, 'infcx, 'tcx> { |
| fields: &'combine mut CombineFields<'infcx, 'tcx>, |
| a_is_expected: bool, |
| } |
| |
| impl<'combine, 'infcx, 'tcx> Lub<'combine, 'infcx, 'tcx> { |
| pub fn new( |
| fields: &'combine mut CombineFields<'infcx, 'tcx>, |
| a_is_expected: bool, |
| ) -> Lub<'combine, 'infcx, 'tcx> { |
| Lub { fields: fields, a_is_expected: a_is_expected } |
| } |
| } |
| |
| impl TypeRelation<'tcx> for Lub<'combine, 'infcx, 'tcx> { |
| fn tag(&self) -> &'static str { "Lub" } |
| |
| fn tcx(&self) -> TyCtxt<'tcx> { self.fields.tcx() } |
| |
| fn param_env(&self) -> ty::ParamEnv<'tcx> { self.fields.param_env } |
| |
| fn a_is_expected(&self) -> bool { self.a_is_expected } |
| |
| fn relate_with_variance<T: Relate<'tcx>>(&mut self, |
| variance: ty::Variance, |
| a: &T, |
| b: &T) |
| -> RelateResult<'tcx, T> |
| { |
| match variance { |
| ty::Invariant => self.fields.equate(self.a_is_expected).relate(a, b), |
| ty::Covariant => self.relate(a, b), |
| // FIXME(#41044) -- not correct, need test |
| ty::Bivariant => Ok(a.clone()), |
| ty::Contravariant => self.fields.glb(self.a_is_expected).relate(a, b), |
| } |
| } |
| |
| fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { |
| lattice::super_lattice_tys(self, a, b) |
| } |
| |
| fn regions(&mut self, a: ty::Region<'tcx>, b: ty::Region<'tcx>) |
| -> RelateResult<'tcx, ty::Region<'tcx>> { |
| debug!("{}.regions({:?}, {:?})", |
| self.tag(), |
| a, |
| b); |
| |
| let origin = Subtype(box self.fields.trace.clone()); |
| Ok(self.fields.infcx.borrow_region_constraints().lub_regions(self.tcx(), origin, a, b)) |
| } |
| |
| fn consts( |
| &mut self, |
| a: &'tcx ty::Const<'tcx>, |
| b: &'tcx ty::Const<'tcx>, |
| ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> { |
| self.fields.infcx.super_combine_consts(self, a, b) |
| } |
| |
| fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>) |
| -> RelateResult<'tcx, ty::Binder<T>> |
| where T: Relate<'tcx> |
| { |
| debug!("binders(a={:?}, b={:?})", a, b); |
| |
| // When higher-ranked types are involved, computing the LUB is |
| // very challenging, switch to invariance. This is obviously |
| // overly conservative but works ok in practice. |
| self.relate_with_variance(ty::Variance::Invariant, a, b)?; |
| Ok(a.clone()) |
| } |
| } |
| |
| impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Lub<'combine, 'infcx, 'tcx> { |
| fn infcx(&self) -> &'infcx InferCtxt<'infcx, 'tcx> { |
| self.fields.infcx |
| } |
| |
| fn cause(&self) -> &ObligationCause<'tcx> { |
| &self.fields.trace.cause |
| } |
| |
| fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> { |
| let mut sub = self.fields.sub(self.a_is_expected); |
| sub.relate(&a, &v)?; |
| sub.relate(&b, &v)?; |
| Ok(()) |
| } |
| } |