| // Copyright 2012 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| use super::combine::CombineFields; |
| use super::SubregionOrigin; |
| use super::type_variable::{SubtypeOf, SupertypeOf}; |
| |
| use ty::{self, Ty, TyCtxt}; |
| use ty::TyVar; |
| use ty::relate::{Cause, Relate, RelateResult, TypeRelation}; |
| use traits::PredicateObligations; |
| use std::mem; |
| |
| /// Ensures `a` is made a subtype of `b`. Returns `a` on success. |
| pub struct Sub<'a, 'gcx: 'a+'tcx, 'tcx: 'a> { |
| fields: CombineFields<'a, 'gcx, 'tcx>, |
| } |
| |
| impl<'a, 'gcx, 'tcx> Sub<'a, 'gcx, 'tcx> { |
| pub fn new(f: CombineFields<'a, 'gcx, 'tcx>) -> Sub<'a, 'gcx, 'tcx> { |
| Sub { fields: f } |
| } |
| |
| pub fn obligations(self) -> PredicateObligations<'tcx> { |
| self.fields.obligations |
| } |
| } |
| |
| impl<'a, 'gcx, 'tcx> TypeRelation<'a, 'gcx, 'tcx> for Sub<'a, 'gcx, 'tcx> { |
| fn tag(&self) -> &'static str { "Sub" } |
| fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> { self.fields.infcx.tcx } |
| fn a_is_expected(&self) -> bool { self.fields.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().relate(a, b), |
| ty::Covariant => self.relate(a, b), |
| ty::Bivariant => self.fields.bivariate().relate(a, b), |
| ty::Contravariant => self.fields.switch_expected().sub().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_id)), &ty::TyInfer(TyVar(b_id))) => { |
| infcx.type_variables |
| .borrow_mut() |
| .relate_vars(a_id, SubtypeOf, b_id); |
| Ok(a) |
| } |
| (&ty::TyInfer(TyVar(a_id)), _) => { |
| self.fields |
| .switch_expected() |
| .instantiate(b, SupertypeOf, a_id)?; |
| Ok(a) |
| } |
| (_, &ty::TyInfer(TyVar(b_id))) => { |
| self.fields.instantiate(a, SubtypeOf, b_id)?; |
| 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, b: ty::Region) -> RelateResult<'tcx, ty::Region> { |
| 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.region_vars.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) |
| } |
| } |