| use super::SubregionOrigin; |
| use super::combine::{CombineFields, RelationDir}; |
| |
| use crate::traits::Obligation; |
| use crate::ty::{self, Ty, TyCtxt}; |
| use crate::ty::TyVar; |
| use crate::ty::fold::TypeFoldable; |
| use crate::ty::relate::{Cause, Relate, RelateResult, TypeRelation}; |
| use std::mem; |
| |
| /// Ensures `a` is made a subtype of `b`. Returns `a` on success. |
| pub struct Sub<'combine, 'infcx: 'combine, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> { |
| fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>, |
| a_is_expected: bool, |
| } |
| |
| impl<'combine, 'infcx, 'gcx, 'tcx> Sub<'combine, 'infcx, 'gcx, 'tcx> { |
| pub fn new(f: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>, a_is_expected: bool) |
| -> Sub<'combine, 'infcx, 'gcx, 'tcx> |
| { |
| Sub { fields: f, a_is_expected: a_is_expected } |
| } |
| |
| fn with_expected_switched<R, F: FnOnce(&mut Self) -> R>(&mut self, f: F) -> R { |
| self.a_is_expected = !self.a_is_expected; |
| let result = f(self); |
| self.a_is_expected = !self.a_is_expected; |
| result |
| } |
| } |
| |
| impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx> |
| for Sub<'combine, 'infcx, 'gcx, 'tcx> |
| { |
| fn tag(&self) -> &'static str { "Sub" } |
| fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> { self.fields.infcx.tcx } |
| fn a_is_expected(&self) -> bool { self.a_is_expected } |
| |
| fn with_cause<F,R>(&mut self, cause: Cause, f: F) -> R |
| where F: FnOnce(&mut Self) -> R |
| { |
| debug!("sub with_cause={:?}", cause); |
| let old_cause = mem::replace(&mut self.fields.cause, Some(cause)); |
| let r = f(self); |
| debug!("sub old_cause={:?}", old_cause); |
| self.fields.cause = old_cause; |
| r |
| } |
| |
| 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), |
| ty::Bivariant => Ok(a.clone()), |
| ty::Contravariant => self.with_expected_switched(|this| { this.relate(b, a) }), |
| } |
| } |
| |
| fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { |
| debug!("{}.tys({:?}, {:?})", self.tag(), a, b); |
| |
| if a == b { return Ok(a); } |
| |
| let infcx = self.fields.infcx; |
| let a = infcx.type_variables.borrow_mut().replace_if_possible(a); |
| let b = infcx.type_variables.borrow_mut().replace_if_possible(b); |
| match (&a.sty, &b.sty) { |
| (&ty::Infer(TyVar(a_vid)), &ty::Infer(TyVar(b_vid))) => { |
| // Shouldn't have any LBR here, so we can safely put |
| // this under a binder below without fear of accidental |
| // capture. |
| assert!(!a.has_escaping_bound_vars()); |
| assert!(!b.has_escaping_bound_vars()); |
| |
| // can't make progress on `A <: B` if both A and B are |
| // type variables, so record an obligation. We also |
| // have to record in the `type_variables` tracker that |
| // the two variables are equal modulo subtyping, which |
| // is important to the occurs check later on. |
| infcx.type_variables.borrow_mut().sub(a_vid, b_vid); |
| self.fields.obligations.push( |
| Obligation::new( |
| self.fields.trace.cause.clone(), |
| self.fields.param_env, |
| ty::Predicate::Subtype( |
| ty::Binder::dummy(ty::SubtypePredicate { |
| a_is_expected: self.a_is_expected, |
| a, |
| b, |
| })))); |
| |
| Ok(a) |
| } |
| (&ty::Infer(TyVar(a_id)), _) => { |
| self.fields |
| .instantiate(b, RelationDir::SupertypeOf, a_id, !self.a_is_expected)?; |
| Ok(a) |
| } |
| (_, &ty::Infer(TyVar(b_id))) => { |
| self.fields.instantiate(a, RelationDir::SubtypeOf, b_id, self.a_is_expected)?; |
| Ok(a) |
| } |
| |
| (&ty::Error, _) | (_, &ty::Error) => { |
| infcx.set_tainted_by_errors(); |
| Ok(self.tcx().types.err) |
| } |
| |
| _ => { |
| self.fields.infcx.super_combine_tys(self, a, b)?; |
| Ok(a) |
| } |
| } |
| } |
| |
| fn regions(&mut self, a: ty::Region<'tcx>, b: ty::Region<'tcx>) |
| -> RelateResult<'tcx, ty::Region<'tcx>> { |
| debug!("{}.regions({:?}, {:?}) self.cause={:?}", |
| self.tag(), a, b, self.fields.cause); |
| |
| // FIXME -- we have more fine-grained information available |
| // from the "cause" field, we could perhaps give more tailored |
| // error messages. |
| let origin = SubregionOrigin::Subtype(self.fields.trace.clone()); |
| self.fields.infcx.borrow_region_constraints() |
| .make_subregion(origin, a, b); |
| |
| Ok(a) |
| } |
| |
| fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>) |
| -> RelateResult<'tcx, ty::Binder<T>> |
| where T: Relate<'tcx> |
| { |
| self.fields.higher_ranked_sub(a, b, self.a_is_expected) |
| } |
| } |