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Diffstat (limited to '')
-rw-r--r-- | compiler/rustc_infer/src/infer/lub.rs | 144 |
1 files changed, 144 insertions, 0 deletions
diff --git a/compiler/rustc_infer/src/infer/lub.rs b/compiler/rustc_infer/src/infer/lub.rs new file mode 100644 index 000000000..9f96d52c8 --- /dev/null +++ b/compiler/rustc_infer/src/infer/lub.rs @@ -0,0 +1,144 @@ +//! Least upper bound. See [`lattice`]. + +use super::combine::CombineFields; +use super::lattice::{self, LatticeDir}; +use super::InferCtxt; +use super::Subtype; + +use crate::infer::combine::ConstEquateRelation; +use crate::traits::{ObligationCause, PredicateObligation}; +use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation}; +use rustc_middle::ty::{self, Ty, TyCtxt}; + +/// "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, a_is_expected } + } +} + +impl<'tcx> TypeRelation<'tcx> for Lub<'_, '_, '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, + _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.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::new(self.fields.trace.clone())); + 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>, + { + 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 LUB 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<'tcx> ConstEquateRelation<'tcx> for Lub<'_, '_, 'tcx> { + fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>) { + self.fields.add_const_equate_obligation(self.a_is_expected, a, b); + } +} + +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 add_obligations(&mut self, obligations: Vec<PredicateObligation<'tcx>>) { + self.fields.obligations.extend(obligations) + } + + 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(()) + } + + fn define_opaque_types(&self) -> bool { + self.fields.define_opaque_types + } +} |