| //! Greatest lower bound. See [`lattice`]. |
| |
| use super::combine::{CombineFields, ObligationEmittingRelation}; |
| use super::lattice::{self, LatticeDir}; |
| use super::InferCtxt; |
| use super::Subtype; |
| |
| use crate::traits::{ObligationCause, PredicateObligations}; |
| use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation}; |
| use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt}; |
| |
| /// "Greatest lower bound" (common subtype) |
| pub struct Glb<'combine, 'infcx, 'tcx> { |
| fields: &'combine mut CombineFields<'infcx, 'tcx>, |
| a_is_expected: bool, |
| } |
| |
| impl<'combine, 'infcx, 'tcx> Glb<'combine, 'infcx, 'tcx> { |
| pub fn new( |
| fields: &'combine mut CombineFields<'infcx, 'tcx>, |
| a_is_expected: bool, |
| ) -> Glb<'combine, 'infcx, 'tcx> { |
| Glb { fields, a_is_expected } |
| } |
| } |
| |
| impl<'tcx> TypeRelation<'tcx> for Glb<'_, '_, 'tcx> { |
| fn tag(&self) -> &'static str { |
| "Glb" |
| } |
| |
| fn intercrate(&self) -> bool { |
| assert!(!self.fields.infcx.intercrate); |
| false |
| } |
| |
| 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 mark_ambiguous(&mut self) { |
| bug!("mark_ambiguous used outside of coherence"); |
| } |
| |
| fn relate_with_variance<T: Relate<'tcx>>( |
| &mut self, |
| variance: ty::Variance, |
| _info: ty::VarianceDiagInfo<'tcx>, |
| 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), |
| ty::Contravariant => self.fields.lub(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::new(self.fields.trace.clone())); |
| // GLB(&'static u8, &'a u8) == &RegionLUB('static, 'a) u8 == &'static u8 |
| Ok(self.fields.infcx.inner.borrow_mut().unwrap_region_constraints().lub_regions( |
| self.tcx(), |
| origin, |
| a, |
| b, |
| )) |
| } |
| |
| fn consts( |
| &mut self, |
| a: ty::Const<'tcx>, |
| b: ty::Const<'tcx>, |
| ) -> RelateResult<'tcx, ty::Const<'tcx>> { |
| self.fields.infcx.super_combine_consts(self, a, b) |
| } |
| |
| fn binders<T>( |
| &mut self, |
| a: ty::Binder<'tcx, T>, |
| b: ty::Binder<'tcx, T>, |
| ) -> RelateResult<'tcx, ty::Binder<'tcx, T>> |
| where |
| T: Relate<'tcx>, |
| { |
| // GLB of a binder and itself is just itself |
| if a == b { |
| return Ok(a); |
| } |
| |
| debug!("binders(a={:?}, b={:?})", a, b); |
| if a.skip_binder().has_escaping_bound_vars() || b.skip_binder().has_escaping_bound_vars() { |
| // When higher-ranked types are involved, computing the GLB is |
| // very challenging, switch to invariance. This is obviously |
| // overly conservative but works ok in practice. |
| self.relate_with_variance( |
| ty::Variance::Invariant, |
| ty::VarianceDiagInfo::default(), |
| a, |
| b, |
| )?; |
| Ok(a) |
| } else { |
| Ok(ty::Binder::dummy(self.relate(a.skip_binder(), b.skip_binder())?)) |
| } |
| } |
| } |
| |
| impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Glb<'combine, 'infcx, 'tcx> { |
| fn infcx(&self) -> &'infcx InferCtxt<'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(v, a)?; |
| sub.relate(v, b)?; |
| Ok(()) |
| } |
| |
| fn define_opaque_types(&self) -> bool { |
| self.fields.define_opaque_types |
| } |
| } |
| |
| impl<'tcx> ObligationEmittingRelation<'tcx> for Glb<'_, '_, 'tcx> { |
| fn register_predicates(&mut self, obligations: impl IntoIterator<Item: ty::ToPredicate<'tcx>>) { |
| self.fields.register_predicates(obligations); |
| } |
| |
| fn register_obligations(&mut self, obligations: PredicateObligations<'tcx>) { |
| self.fields.register_obligations(obligations); |
| } |
| } |