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use super::SubregionOrigin;
use super::combine::{CombineFields, RelationDir};
use traits::Obligation;
use ty::{self, Ty, TyCtxt};
use ty::TyVar;
use ty::fold::TypeFoldable;
use ty::relate::{Cause, Relate, RelateResult, TypeRelation};
use std::mem;
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::TyInfer(TyVar(a_vid)), &ty::TyInfer(TyVar(b_vid))) => {
assert!(!a.has_escaping_regions());
assert!(!b.has_escaping_regions());
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::TyInfer(TyVar(a_id)), _) => {
self.fields
.instantiate(b, RelationDir::SupertypeOf, a_id, !self.a_is_expected)?;
Ok(a)
}
(_, &ty::TyInfer(TyVar(b_id))) => {
self.fields.instantiate(a, RelationDir::SubtypeOf, b_id, self.a_is_expected)?;
Ok(a)
}
(&ty::TyError, _) | (_, &ty::TyError) => {
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);
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)
}
}