use super::combine::{CombineFields, RelationDir}; use super::SubregionOrigin; use crate::infer::combine::ConstEquateRelation; use crate::traits::Obligation; use rustc_middle::ty::relate::{Cause, Relate, RelateResult, TypeRelation}; use rustc_middle::ty::visit::TypeVisitable; use rustc_middle::ty::TyVar; use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt}; use std::mem; /// Ensures `a` is made a subtype of `b`. Returns `a` on success. pub struct Sub<'combine, 'a, 'tcx> { fields: &'combine mut CombineFields<'a, 'tcx>, a_is_expected: bool, } impl<'combine, 'infcx, 'tcx> Sub<'combine, 'infcx, 'tcx> { pub fn new( f: &'combine mut CombineFields<'infcx, 'tcx>, a_is_expected: bool, ) -> Sub<'combine, 'infcx, 'tcx> { Sub { fields: f, a_is_expected } } fn with_expected_switched 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<'tcx> TypeRelation<'tcx> for Sub<'_, '_, 'tcx> { fn tag(&self) -> &'static str { "Sub" } fn tcx(&self) -> TyCtxt<'tcx> { self.fields.infcx.tcx } fn param_env(&self) -> ty::ParamEnv<'tcx> { self.fields.param_env } fn a_is_expected(&self) -> bool { self.a_is_expected } fn with_cause(&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>( &mut self, variance: ty::Variance, _info: ty::VarianceDiagInfo<'tcx>, 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), ty::Contravariant => self.with_expected_switched(|this| this.relate(b, a)), } } #[instrument(skip(self), level = "debug")] fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { if a == b { return Ok(a); } let infcx = self.fields.infcx; let a = infcx.inner.borrow_mut().type_variables().replace_if_possible(a); let b = infcx.inner.borrow_mut().type_variables().replace_if_possible(b); match (a.kind(), b.kind()) { (&ty::Infer(TyVar(_)), &ty::Infer(TyVar(_))) => { // 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. self.fields.obligations.push(Obligation::new( self.fields.trace.cause.clone(), self.fields.param_env, ty::Binder::dummy(ty::PredicateKind::Subtype(ty::SubtypePredicate { a_is_expected: self.a_is_expected, a, b, })) .to_predicate(self.tcx()), )); 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().ty_error()) } (&ty::Opaque(a_def_id, _), &ty::Opaque(b_def_id, _)) if a_def_id == b_def_id => { self.fields.infcx.super_combine_tys(self, a, b)?; Ok(a) } (&ty::Opaque(did, ..), _) | (_, &ty::Opaque(did, ..)) if self.fields.define_opaque_types && did.is_local() => { self.fields.obligations.extend( infcx .handle_opaque_type( a, b, self.a_is_expected, &self.fields.trace.cause, self.param_env(), )? .obligations, ); Ok(a) } // Optimization of GeneratorWitness relation since we know that all // free regions are replaced with bound regions during construction. // This greatly speeds up subtyping of GeneratorWitness. (&ty::GeneratorWitness(a_types), &ty::GeneratorWitness(b_types)) => { let a_types = infcx.tcx.anonymize_bound_vars(a_types); let b_types = infcx.tcx.anonymize_bound_vars(b_types); if a_types.bound_vars() == b_types.bound_vars() { let (a_types, b_types) = infcx.replace_bound_vars_with_placeholders( a_types.map_bound(|a_types| (a_types, b_types.skip_binder())), ); for (a, b) in std::iter::zip(a_types, b_types) { self.relate(a, b)?; } Ok(a) } else { Err(ty::error::TypeError::Sorts(ty::relate::expected_found(self, a, b))) } } _ => { 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(Box::new(self.fields.trace.clone())); self.fields .infcx .inner .borrow_mut() .unwrap_region_constraints() .make_subregion(origin, a, b); Ok(a) } fn consts( &mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>, ) -> RelateResult<'tcx, ty::Const<'tcx>> { self.fields.infcx.super_combine_consts(self, a, b) } fn binders( &mut self, a: ty::Binder<'tcx, T>, b: ty::Binder<'tcx, T>, ) -> RelateResult<'tcx, ty::Binder<'tcx, T>> where T: Relate<'tcx>, { self.fields.higher_ranked_sub(a, b, self.a_is_expected)?; Ok(a) } } impl<'tcx> ConstEquateRelation<'tcx> for Sub<'_, '_, 'tcx> { fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>) { self.fields.add_const_equate_obligation(self.a_is_expected, a, b); } }