1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 use super::SubregionOrigin;
12 use super::combine::CombineFields;
13 use super::type_variable::{SubtypeOf, SupertypeOf};
15 use ty::{self, Ty, TyCtxt};
17 use ty::relate::{Cause, Relate, RelateResult, TypeRelation};
20 /// Ensures `a` is made a subtype of `b`. Returns `a` on success.
21 pub struct Sub<'combine, 'infcx: 'combine, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> {
22 fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>,
26 impl<'combine, 'infcx, 'gcx, 'tcx> Sub<'combine, 'infcx, 'gcx, 'tcx> {
27 pub fn new(f: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>, a_is_expected: bool)
28 -> Sub<'combine, 'infcx, 'gcx, 'tcx>
30 Sub { fields: f, a_is_expected: a_is_expected }
33 fn with_expected_switched<R, F: FnOnce(&mut Self) -> R>(&mut self, f: F) -> R {
34 self.a_is_expected = !self.a_is_expected;
36 self.a_is_expected = !self.a_is_expected;
41 impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
42 for Sub<'combine, 'infcx, 'gcx, 'tcx>
44 fn tag(&self) -> &'static str { "Sub" }
45 fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> { self.fields.infcx.tcx }
46 fn a_is_expected(&self) -> bool { self.a_is_expected }
48 fn with_cause<F,R>(&mut self, cause: Cause, f: F) -> R
49 where F: FnOnce(&mut Self) -> R
51 debug!("sub with_cause={:?}", cause);
52 let old_cause = mem::replace(&mut self.fields.cause, Some(cause));
54 debug!("sub old_cause={:?}", old_cause);
55 self.fields.cause = old_cause;
59 fn relate_with_variance<T: Relate<'tcx>>(&mut self,
60 variance: ty::Variance,
63 -> RelateResult<'tcx, T>
66 ty::Invariant => self.fields.equate(self.a_is_expected).relate(a, b),
67 ty::Covariant => self.relate(a, b),
68 ty::Bivariant => self.fields.bivariate(self.a_is_expected).relate(a, b),
69 ty::Contravariant => self.with_expected_switched(|this| { this.relate(b, a) }),
73 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
74 debug!("{}.tys({:?}, {:?})", self.tag(), a, b);
76 if a == b { return Ok(a); }
78 let infcx = self.fields.infcx;
79 let a = infcx.type_variables.borrow_mut().replace_if_possible(a);
80 let b = infcx.type_variables.borrow_mut().replace_if_possible(b);
81 match (&a.sty, &b.sty) {
82 (&ty::TyInfer(TyVar(a_id)), &ty::TyInfer(TyVar(b_id))) => {
85 .relate_vars(a_id, SubtypeOf, b_id);
88 (&ty::TyInfer(TyVar(a_id)), _) => {
90 .instantiate(b, SupertypeOf, a_id, !self.a_is_expected)?;
93 (_, &ty::TyInfer(TyVar(b_id))) => {
94 self.fields.instantiate(a, SubtypeOf, b_id, self.a_is_expected)?;
98 (&ty::TyError, _) | (_, &ty::TyError) => {
99 infcx.set_tainted_by_errors();
100 Ok(self.tcx().types.err)
104 self.fields.infcx.super_combine_tys(self, a, b)?;
110 fn regions(&mut self, a: &'tcx ty::Region, b: &'tcx ty::Region)
111 -> RelateResult<'tcx, &'tcx ty::Region> {
112 debug!("{}.regions({:?}, {:?}) self.cause={:?}",
113 self.tag(), a, b, self.fields.cause);
115 // FIXME -- we have more fine-grained information available
116 // from the "cause" field, we could perhaps give more tailored
118 let origin = SubregionOrigin::Subtype(self.fields.trace.clone());
119 self.fields.infcx.region_vars.make_subregion(origin, a, b);
124 fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
125 -> RelateResult<'tcx, ty::Binder<T>>
126 where T: Relate<'tcx>
128 self.fields.higher_ranked_sub(a, b, self.a_is_expected)