diff --git a/src/librustc/middle/traits/coherence.rs b/src/librustc/middle/traits/coherence.rs index 3a7522cafee..e199a60c370 100644 --- a/src/librustc/middle/traits/coherence.rs +++ b/src/librustc/middle/traits/coherence.rs @@ -10,24 +10,27 @@ //! See `doc.rs` for high-level documentation +use super::Normalized; use super::SelectionContext; -use super::{Obligation, ObligationCause}; +use super::{ObligationCause}; +use super::PredicateObligation; use super::project; use super::util; use middle::subst::{Subst, TypeSpace}; -use middle::ty::{self, Ty}; -use middle::infer::InferCtxt; +use middle::ty::{self, ToPolyTraitRef, Ty}; +use middle::infer::{self, InferCtxt}; use std::collections::HashSet; use std::rc::Rc; use syntax::ast; use syntax::codemap::DUMMY_SP; use util::ppaux::Repr; -pub fn impl_can_satisfy(infcx: &InferCtxt, - impl1_def_id: ast::DefId, - impl2_def_id: ast::DefId) - -> bool +/// True if there exist types that satisfy both of the two given impls. +pub fn overlapping_impls(infcx: &InferCtxt, + impl1_def_id: ast::DefId, + impl2_def_id: ast::DefId) + -> bool { debug!("impl_can_satisfy(\ impl1_def_id={}, \ @@ -35,28 +38,68 @@ pub fn impl_can_satisfy(infcx: &InferCtxt, impl1_def_id.repr(infcx.tcx), impl2_def_id.repr(infcx.tcx)); - let param_env = ty::empty_parameter_environment(infcx.tcx); - let mut selcx = SelectionContext::intercrate(infcx, ¶m_env); - let cause = ObligationCause::dummy(); + let param_env = &ty::empty_parameter_environment(infcx.tcx); + let selcx = &mut SelectionContext::intercrate(infcx, param_env); + infcx.probe(|_| { + overlap(selcx, impl1_def_id, impl2_def_id) || overlap(selcx, impl2_def_id, impl1_def_id) + }) +} - // `impl1` provides an implementation of `Foo for Z`. - let impl1_substs = - util::fresh_substs_for_impl(infcx, DUMMY_SP, impl1_def_id); - let impl1_trait_ref = - (*ty::impl_trait_ref(infcx.tcx, impl1_def_id).unwrap()).subst(infcx.tcx, &impl1_substs); - let impl1_trait_ref = - project::normalize(&mut selcx, cause.clone(), &impl1_trait_ref); +/// Can the types from impl `a` be used to satisfy impl `b`? +/// (Including all conditions) +fn overlap(selcx: &mut SelectionContext, + a_def_id: ast::DefId, + b_def_id: ast::DefId) + -> bool +{ + let (a_trait_ref, a_obligations) = impl_trait_ref_and_oblig(selcx, a_def_id); + let (b_trait_ref, b_obligations) = impl_trait_ref_and_oblig(selcx, b_def_id); - // Determine whether `impl2` can provide an implementation for those - // same types. - let obligation = Obligation::new(cause, - ty::Binder(ty::TraitPredicate { - trait_ref: Rc::new(impl1_trait_ref.value), - })); - debug!("impl_can_satisfy(obligation={})", obligation.repr(infcx.tcx)); - selcx.evaluate_impl(impl2_def_id, &obligation) && - impl1_trait_ref.obligations.iter().all( - |o| selcx.evaluate_obligation(o)) + // Does `a <: b` hold? If not, no overlap. + if let Err(_) = infer::mk_sub_poly_trait_refs(selcx.infcx(), + true, + infer::Misc(DUMMY_SP), + a_trait_ref.to_poly_trait_ref(), + b_trait_ref.to_poly_trait_ref()) { + return false; + } + + // Are any of the obligations unsatisfiable? If so, no overlap. + a_obligations.iter() + .chain(b_obligations.iter()) + .all(|o| selcx.evaluate_obligation(o)) +} + +/// Instantiate fresh variables for all bound parameters of the impl +/// and return the impl trait ref with those variables substituted. +fn impl_trait_ref_and_oblig<'a,'tcx>(selcx: &mut SelectionContext<'a,'tcx>, + impl_def_id: ast::DefId) + -> (Rc>, + Vec>) +{ + let impl_substs = + &util::fresh_substs_for_impl(selcx.infcx(), DUMMY_SP, impl_def_id); + let impl_trait_ref = + ty::impl_trait_ref(selcx.tcx(), impl_def_id).unwrap(); + let impl_trait_ref = + impl_trait_ref.subst(selcx.tcx(), impl_substs); + let Normalized { value: impl_trait_ref, obligations: normalization_obligations1 } = + project::normalize(selcx, ObligationCause::dummy(), &impl_trait_ref); + + let predicates = ty::lookup_predicates(selcx.tcx(), impl_def_id); + let predicates = predicates.instantiate(selcx.tcx(), impl_substs); + let Normalized { value: predicates, obligations: normalization_obligations2 } = + project::normalize(selcx, ObligationCause::dummy(), &predicates); + let impl_obligations = + util::predicates_for_generics(selcx.tcx(), ObligationCause::dummy(), 0, &predicates); + + let impl_obligations: Vec<_> = + impl_obligations.into_iter() + .chain(normalization_obligations1.into_iter()) + .chain(normalization_obligations2.into_iter()) + .collect(); + + (impl_trait_ref, impl_obligations) } pub enum OrphanCheckErr<'tcx> { diff --git a/src/librustc/middle/traits/mod.rs b/src/librustc/middle/traits/mod.rs index 83090dd72aa..2e4bcdf0478 100644 --- a/src/librustc/middle/traits/mod.rs +++ b/src/librustc/middle/traits/mod.rs @@ -28,6 +28,7 @@ use util::ppaux::{Repr, UserString}; pub use self::error_reporting::report_fulfillment_errors; pub use self::error_reporting::suggest_new_overflow_limit; pub use self::coherence::orphan_check; +pub use self::coherence::overlapping_impls; pub use self::coherence::OrphanCheckErr; pub use self::fulfill::{FulfillmentContext, RegionObligation}; pub use self::project::MismatchedProjectionTypes; @@ -270,16 +271,6 @@ pub struct VtableObjectData<'tcx> { pub object_ty: Ty<'tcx>, } -/// True if there exist types that satisfy both of the two given impls. -pub fn overlapping_impls(infcx: &InferCtxt, - impl1_def_id: ast::DefId, - impl2_def_id: ast::DefId) - -> bool -{ - coherence::impl_can_satisfy(infcx, impl1_def_id, impl2_def_id) && - coherence::impl_can_satisfy(infcx, impl2_def_id, impl1_def_id) -} - /// Creates predicate obligations from the generic bounds. pub fn predicates_for_generics<'tcx>(tcx: &ty::ctxt<'tcx>, cause: ObligationCause<'tcx>, diff --git a/src/test/compile-fail/coherence-subtyping.rs b/src/test/compile-fail/coherence-subtyping.rs new file mode 100644 index 00000000000..897cb083f84 --- /dev/null +++ b/src/test/compile-fail/coherence-subtyping.rs @@ -0,0 +1,50 @@ +// Copyright 2015 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 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// Test that two distinct impls which match subtypes of one another +// yield coherence errors (or not) depending on the variance. + +trait Contravariant { + fn foo(&self) { } +} + +impl Contravariant for for<'a,'b> fn(&'a u8, &'b u8) { + //~^ ERROR E0119 +} + +impl Contravariant for for<'a> fn(&'a u8, &'a u8) { +} + +/////////////////////////////////////////////////////////////////////////// + +trait Covariant { + fn foo(&self) { } +} + +impl Covariant for for<'a,'b> fn(&'a u8, &'b u8) { + //~^ ERROR E0119 +} + +impl Covariant for for<'a> fn(&'a u8, &'a u8) { +} + +/////////////////////////////////////////////////////////////////////////// + +trait Invariant { + fn foo(&self) -> Self { } +} + +impl Invariant for for<'a,'b> fn(&'a u8, &'b u8) { +} + +impl Invariant for for<'a> fn(&'a u8, &'a u8) { +} + +fn main() { }