Extend coherence check to understand subtyping.

This commit is contained in:
Niko Matsakis 2015-02-12 12:42:02 -05:00
parent 91eedfe18b
commit 8c841f2a31
3 changed files with 121 additions and 37 deletions

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@ -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, &param_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<X,Y> 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<ty::TraitRef<'tcx>>,
Vec<PredicateObligation<'tcx>>)
{
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> {

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@ -28,6 +28,7 @@
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>,

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@ -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 <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.
// 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() { }