/
equate.rs
151 lines (124 loc) · 5.18 KB
/
equate.rs
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use super::combine::{CombineFields, RelationDir, const_unification_error};
use super::Subtype;
use crate::hir::def_id::DefId;
use crate::ty::{self, Ty, TyCtxt, InferConst};
use crate::ty::TyVar;
use crate::ty::subst::SubstsRef;
use crate::ty::relate::{self, Relate, RelateResult, TypeRelation};
use crate::mir::interpret::ConstValue;
use crate::infer::unify_key::replace_if_possible;
/// Ensures `a` is made equal to `b`. Returns `a` on success.
pub struct Equate<'combine, 'infcx: 'combine, 'tcx: 'infcx> {
fields: &'combine mut CombineFields<'infcx, 'tcx>,
a_is_expected: bool,
}
impl<'combine, 'infcx, 'tcx> Equate<'combine, 'infcx, 'tcx> {
pub fn new(
fields: &'combine mut CombineFields<'infcx, 'tcx>,
a_is_expected: bool,
) -> Equate<'combine, 'infcx, 'tcx> {
Equate { fields: fields, a_is_expected: a_is_expected }
}
}
impl TypeRelation<'tcx> for Equate<'combine, 'infcx, 'tcx> {
fn tag(&self) -> &'static str { "Equate" }
fn tcx(&self) -> TyCtxt<'tcx> { self.fields.tcx() }
fn a_is_expected(&self) -> bool { self.a_is_expected }
fn relate_item_substs(&mut self,
_item_def_id: DefId,
a_subst: SubstsRef<'tcx>,
b_subst: SubstsRef<'tcx>)
-> RelateResult<'tcx, SubstsRef<'tcx>>
{
// N.B., once we are equating types, we don't care about
// variance, so don't try to lookup the variance here. This
// also avoids some cycles (e.g., #41849) since looking up
// variance requires computing types which can require
// performing trait matching (which then performs equality
// unification).
relate::relate_substs(self, None, a_subst, b_subst)
}
fn relate_with_variance<T: Relate<'tcx>>(&mut self,
_: ty::Variance,
a: &T,
b: &T)
-> RelateResult<'tcx, T>
{
self.relate(a, b)
}
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);
debug!("{}.tys: replacements ({:?}, {:?})", self.tag(), a, b);
match (&a.sty, &b.sty) {
(&ty::Infer(TyVar(a_id)), &ty::Infer(TyVar(b_id))) => {
infcx.type_variables.borrow_mut().equate(a_id, b_id);
}
(&ty::Infer(TyVar(a_id)), _) => {
self.fields.instantiate(b, RelationDir::EqTo, a_id, self.a_is_expected)?;
}
(_, &ty::Infer(TyVar(b_id))) => {
self.fields.instantiate(a, RelationDir::EqTo, b_id, self.a_is_expected)?;
}
_ => {
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.tag(),
a,
b);
let origin = Subtype(self.fields.trace.clone());
self.fields.infcx.borrow_region_constraints()
.make_eqregion(origin, a, b);
Ok(a)
}
fn consts(
&mut self,
a: &'tcx ty::Const<'tcx>,
b: &'tcx ty::Const<'tcx>,
) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
debug!("{}.consts({:?}, {:?})", self.tag(), a, b);
if a == b { return Ok(a); }
let infcx = self.fields.infcx;
let a = replace_if_possible(infcx.const_unification_table.borrow_mut(), a);
let b = replace_if_possible(infcx.const_unification_table.borrow_mut(), b);
let a_is_expected = self.a_is_expected();
match (a.val, b.val) {
(ConstValue::Infer(InferConst::Var(a_vid)),
ConstValue::Infer(InferConst::Var(b_vid))) => {
infcx.const_unification_table
.borrow_mut()
.unify_var_var(a_vid, b_vid)
.map_err(|e| const_unification_error(a_is_expected, e))?;
return Ok(a);
}
(ConstValue::Infer(InferConst::Var(a_id)), _) => {
self.fields.infcx.unify_const_variable(a_is_expected, a_id, b)?;
return Ok(a);
}
(_, ConstValue::Infer(InferConst::Var(b_id))) => {
self.fields.infcx.unify_const_variable(!a_is_expected, b_id, a)?;
return Ok(a);
}
_ => {}
}
self.fields.infcx.super_combine_consts(self, 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)?;
self.fields.higher_ranked_sub(b, a, self.a_is_expected)
}
}