478 lines
16 KiB
Rust
478 lines
16 KiB
Rust
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use middle::def_id::DefId;
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use middle::infer::InferCtxt;
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use middle::subst::Substs;
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use middle::ty::{self, Ty, ToPredicate, ToPolyTraitRef};
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use syntax::codemap::Span;
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use util::common::ErrorReported;
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use util::nodemap::FnvHashSet;
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use super::{Obligation, ObligationCause, PredicateObligation};
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struct PredicateSet<'a,'tcx:'a> {
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tcx: &'a ty::ctxt<'tcx>,
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set: FnvHashSet<ty::Predicate<'tcx>>,
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}
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impl<'a,'tcx> PredicateSet<'a,'tcx> {
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fn new(tcx: &'a ty::ctxt<'tcx>) -> PredicateSet<'a,'tcx> {
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PredicateSet { tcx: tcx, set: FnvHashSet() }
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}
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fn insert(&mut self, pred: &ty::Predicate<'tcx>) -> bool {
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// We have to be careful here because we want
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//
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// for<'a> Foo<&'a int>
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//
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// and
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//
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// for<'b> Foo<&'b int>
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//
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// to be considered equivalent. So normalize all late-bound
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// regions before we throw things into the underlying set.
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let normalized_pred = match *pred {
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ty::Predicate::Trait(ref data) =>
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ty::Predicate::Trait(self.tcx.anonymize_late_bound_regions(data)),
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ty::Predicate::Equate(ref data) =>
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ty::Predicate::Equate(self.tcx.anonymize_late_bound_regions(data)),
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ty::Predicate::RegionOutlives(ref data) =>
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ty::Predicate::RegionOutlives(self.tcx.anonymize_late_bound_regions(data)),
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ty::Predicate::TypeOutlives(ref data) =>
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ty::Predicate::TypeOutlives(self.tcx.anonymize_late_bound_regions(data)),
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ty::Predicate::Projection(ref data) =>
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ty::Predicate::Projection(self.tcx.anonymize_late_bound_regions(data)),
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ty::Predicate::WellFormed(data) =>
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ty::Predicate::WellFormed(data),
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ty::Predicate::ObjectSafe(data) =>
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ty::Predicate::ObjectSafe(data),
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};
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self.set.insert(normalized_pred)
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}
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}
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///////////////////////////////////////////////////////////////////////////
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// `Elaboration` iterator
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///////////////////////////////////////////////////////////////////////////
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/// "Elaboration" is the process of identifying all the predicates that
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/// are implied by a source predicate. Currently this basically means
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/// walking the "supertraits" and other similar assumptions. For
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/// example, if we know that `T : Ord`, the elaborator would deduce
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/// that `T : PartialOrd` holds as well. Similarly, if we have `trait
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/// Foo : 'static`, and we know that `T : Foo`, then we know that `T :
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/// 'static`.
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pub struct Elaborator<'cx, 'tcx:'cx> {
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tcx: &'cx ty::ctxt<'tcx>,
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stack: Vec<ty::Predicate<'tcx>>,
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visited: PredicateSet<'cx,'tcx>,
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}
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pub fn elaborate_trait_ref<'cx, 'tcx>(
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tcx: &'cx ty::ctxt<'tcx>,
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trait_ref: ty::PolyTraitRef<'tcx>)
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-> Elaborator<'cx, 'tcx>
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{
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elaborate_predicates(tcx, vec![trait_ref.to_predicate()])
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}
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pub fn elaborate_trait_refs<'cx, 'tcx>(
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tcx: &'cx ty::ctxt<'tcx>,
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trait_refs: &[ty::PolyTraitRef<'tcx>])
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-> Elaborator<'cx, 'tcx>
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{
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let predicates = trait_refs.iter()
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.map(|trait_ref| trait_ref.to_predicate())
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.collect();
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elaborate_predicates(tcx, predicates)
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}
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pub fn elaborate_predicates<'cx, 'tcx>(
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tcx: &'cx ty::ctxt<'tcx>,
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mut predicates: Vec<ty::Predicate<'tcx>>)
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-> Elaborator<'cx, 'tcx>
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{
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let mut visited = PredicateSet::new(tcx);
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predicates.retain(|pred| visited.insert(pred));
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Elaborator { tcx: tcx, stack: predicates, visited: visited }
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}
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impl<'cx, 'tcx> Elaborator<'cx, 'tcx> {
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pub fn filter_to_traits(self) -> FilterToTraits<Elaborator<'cx, 'tcx>> {
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FilterToTraits::new(self)
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}
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fn push(&mut self, predicate: &ty::Predicate<'tcx>) {
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match *predicate {
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ty::Predicate::Trait(ref data) => {
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// Predicates declared on the trait.
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let predicates = self.tcx.lookup_super_predicates(data.def_id());
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let mut predicates: Vec<_> =
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predicates.predicates
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.iter()
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.map(|p| p.subst_supertrait(self.tcx, &data.to_poly_trait_ref()))
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.collect();
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debug!("super_predicates: data={:?} predicates={:?}",
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data, predicates);
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// Only keep those bounds that we haven't already
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// seen. This is necessary to prevent infinite
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// recursion in some cases. One common case is when
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// people define `trait Sized: Sized { }` rather than `trait
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// Sized { }`.
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predicates.retain(|r| self.visited.insert(r));
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self.stack.extend(predicates);
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}
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ty::Predicate::WellFormed(..) => {
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// Currently, we do not elaborate WF predicates,
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// although we easily could.
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}
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ty::Predicate::ObjectSafe(..) => {
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// Currently, we do not elaborate object-safe
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// predicates.
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}
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ty::Predicate::Equate(..) => {
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// Currently, we do not "elaborate" predicates like
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// `X == Y`, though conceivably we might. For example,
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// `&X == &Y` implies that `X == Y`.
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}
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ty::Predicate::Projection(..) => {
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// Nothing to elaborate in a projection predicate.
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}
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ty::Predicate::RegionOutlives(..) |
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ty::Predicate::TypeOutlives(..) => {
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// Currently, we do not "elaborate" predicates like
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// `'a : 'b` or `T : 'a`. We could conceivably do
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// more here. For example,
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//
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// &'a int : 'b
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//
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// implies that
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//
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// 'a : 'b
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//
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// and we could get even more if we took WF
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// constraints into account. For example,
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//
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// &'a &'b int : 'c
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//
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// implies that
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//
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// 'b : 'a
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// 'a : 'c
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}
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}
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}
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}
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impl<'cx, 'tcx> Iterator for Elaborator<'cx, 'tcx> {
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type Item = ty::Predicate<'tcx>;
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fn next(&mut self) -> Option<ty::Predicate<'tcx>> {
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// Extract next item from top-most stack frame, if any.
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let next_predicate = match self.stack.pop() {
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Some(predicate) => predicate,
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None => {
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// No more stack frames. Done.
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return None;
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}
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};
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self.push(&next_predicate);
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return Some(next_predicate);
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}
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}
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///////////////////////////////////////////////////////////////////////////
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// Supertrait iterator
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///////////////////////////////////////////////////////////////////////////
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pub type Supertraits<'cx, 'tcx> = FilterToTraits<Elaborator<'cx, 'tcx>>;
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pub fn supertraits<'cx, 'tcx>(tcx: &'cx ty::ctxt<'tcx>,
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trait_ref: ty::PolyTraitRef<'tcx>)
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-> Supertraits<'cx, 'tcx>
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{
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elaborate_trait_ref(tcx, trait_ref).filter_to_traits()
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}
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pub fn transitive_bounds<'cx, 'tcx>(tcx: &'cx ty::ctxt<'tcx>,
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bounds: &[ty::PolyTraitRef<'tcx>])
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-> Supertraits<'cx, 'tcx>
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{
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elaborate_trait_refs(tcx, bounds).filter_to_traits()
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}
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///////////////////////////////////////////////////////////////////////////
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// Iterator over def-ids of supertraits
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pub struct SupertraitDefIds<'cx, 'tcx:'cx> {
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tcx: &'cx ty::ctxt<'tcx>,
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stack: Vec<DefId>,
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visited: FnvHashSet<DefId>,
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}
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pub fn supertrait_def_ids<'cx, 'tcx>(tcx: &'cx ty::ctxt<'tcx>,
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trait_def_id: DefId)
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-> SupertraitDefIds<'cx, 'tcx>
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{
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SupertraitDefIds {
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tcx: tcx,
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stack: vec![trait_def_id],
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visited: Some(trait_def_id).into_iter().collect(),
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}
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}
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impl<'cx, 'tcx> Iterator for SupertraitDefIds<'cx, 'tcx> {
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type Item = DefId;
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fn next(&mut self) -> Option<DefId> {
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let def_id = match self.stack.pop() {
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Some(def_id) => def_id,
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None => { return None; }
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};
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let predicates = self.tcx.lookup_super_predicates(def_id);
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let visited = &mut self.visited;
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self.stack.extend(
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predicates.predicates
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.iter()
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.filter_map(|p| p.to_opt_poly_trait_ref())
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.map(|t| t.def_id())
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.filter(|&super_def_id| visited.insert(super_def_id)));
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Some(def_id)
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}
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}
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///////////////////////////////////////////////////////////////////////////
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// Other
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///////////////////////////////////////////////////////////////////////////
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/// A filter around an iterator of predicates that makes it yield up
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/// just trait references.
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pub struct FilterToTraits<I> {
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base_iterator: I
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}
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impl<I> FilterToTraits<I> {
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fn new(base: I) -> FilterToTraits<I> {
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FilterToTraits { base_iterator: base }
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}
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}
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impl<'tcx,I:Iterator<Item=ty::Predicate<'tcx>>> Iterator for FilterToTraits<I> {
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type Item = ty::PolyTraitRef<'tcx>;
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fn next(&mut self) -> Option<ty::PolyTraitRef<'tcx>> {
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loop {
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match self.base_iterator.next() {
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None => {
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return None;
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}
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Some(ty::Predicate::Trait(data)) => {
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return Some(data.to_poly_trait_ref());
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}
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Some(_) => {
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}
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}
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}
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}
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}
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///////////////////////////////////////////////////////////////////////////
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// Other
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///////////////////////////////////////////////////////////////////////////
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// determine the `self` type, using fresh variables for all variables
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// declared on the impl declaration e.g., `impl<A,B> for Box<[(A,B)]>`
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// would return ($0, $1) where $0 and $1 are freshly instantiated type
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// variables.
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pub fn fresh_type_vars_for_impl<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
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span: Span,
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impl_def_id: DefId)
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-> Substs<'tcx>
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{
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let tcx = infcx.tcx;
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let impl_generics = tcx.lookup_item_type(impl_def_id).generics;
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infcx.fresh_substs_for_generics(span, &impl_generics)
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}
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/// See `super::obligations_for_generics`
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pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
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recursion_depth: usize,
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generic_bounds: &ty::InstantiatedPredicates<'tcx>)
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-> Vec<PredicateObligation<'tcx>>
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{
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debug!("predicates_for_generics(generic_bounds={:?})",
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generic_bounds);
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generic_bounds.predicates.iter().map(|predicate| {
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Obligation { cause: cause.clone(),
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recursion_depth: recursion_depth,
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predicate: predicate.clone() }
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}).collect()
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}
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pub fn trait_ref_for_builtin_bound<'tcx>(
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tcx: &ty::ctxt<'tcx>,
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builtin_bound: ty::BuiltinBound,
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param_ty: Ty<'tcx>)
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-> Result<ty::TraitRef<'tcx>, ErrorReported>
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{
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match tcx.lang_items.from_builtin_kind(builtin_bound) {
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Ok(def_id) => {
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Ok(ty::TraitRef {
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def_id: def_id,
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substs: tcx.mk_substs(Substs::empty().with_self_ty(param_ty))
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})
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}
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Err(e) => {
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tcx.sess.err(&e);
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Err(ErrorReported)
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}
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}
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}
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pub fn predicate_for_trait_ref<'tcx>(
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cause: ObligationCause<'tcx>,
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trait_ref: ty::TraitRef<'tcx>,
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recursion_depth: usize)
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-> PredicateObligation<'tcx>
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{
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Obligation {
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cause: cause,
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recursion_depth: recursion_depth,
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predicate: trait_ref.to_predicate(),
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}
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}
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pub fn predicate_for_trait_def<'tcx>(
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tcx: &ty::ctxt<'tcx>,
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cause: ObligationCause<'tcx>,
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trait_def_id: DefId,
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recursion_depth: usize,
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param_ty: Ty<'tcx>,
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ty_params: Vec<Ty<'tcx>>)
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-> PredicateObligation<'tcx>
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{
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let trait_ref = ty::TraitRef {
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def_id: trait_def_id,
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substs: tcx.mk_substs(Substs::new_trait(ty_params, vec![], param_ty))
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};
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predicate_for_trait_ref(cause, trait_ref, recursion_depth)
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}
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pub fn predicate_for_builtin_bound<'tcx>(
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tcx: &ty::ctxt<'tcx>,
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cause: ObligationCause<'tcx>,
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builtin_bound: ty::BuiltinBound,
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recursion_depth: usize,
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param_ty: Ty<'tcx>)
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-> Result<PredicateObligation<'tcx>, ErrorReported>
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{
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let trait_ref = try!(trait_ref_for_builtin_bound(tcx, builtin_bound, param_ty));
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Ok(predicate_for_trait_ref(cause, trait_ref, recursion_depth))
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}
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/// Cast a trait reference into a reference to one of its super
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/// traits; returns `None` if `target_trait_def_id` is not a
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/// supertrait.
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pub fn upcast<'tcx>(tcx: &ty::ctxt<'tcx>,
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source_trait_ref: ty::PolyTraitRef<'tcx>,
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target_trait_def_id: DefId)
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-> Vec<ty::PolyTraitRef<'tcx>>
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{
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if source_trait_ref.def_id() == target_trait_def_id {
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return vec![source_trait_ref]; // shorcut the most common case
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}
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supertraits(tcx, source_trait_ref)
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.filter(|r| r.def_id() == target_trait_def_id)
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.collect()
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}
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/// Given a trait `trait_ref`, returns the number of vtable entries
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/// that come from `trait_ref`, excluding its supertraits. Used in
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/// computing the vtable base for an upcast trait of a trait object.
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pub fn count_own_vtable_entries<'tcx>(tcx: &ty::ctxt<'tcx>,
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trait_ref: ty::PolyTraitRef<'tcx>)
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-> usize {
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let mut entries = 0;
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// Count number of methods and add them to the total offset.
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// Skip over associated types and constants.
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for trait_item in &tcx.trait_items(trait_ref.def_id())[..] {
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if let ty::MethodTraitItem(_) = *trait_item {
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entries += 1;
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}
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}
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entries
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}
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/// Given an upcast trait object described by `object`, returns the
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/// index of the method `method_def_id` (which should be part of
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/// `object.upcast_trait_ref`) within the vtable for `object`.
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pub fn get_vtable_index_of_object_method<'tcx>(tcx: &ty::ctxt<'tcx>,
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object: &super::VtableObjectData<'tcx>,
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method_def_id: DefId) -> usize {
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// Count number of methods preceding the one we are selecting and
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// add them to the total offset.
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// Skip over associated types and constants.
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let mut entries = object.vtable_base;
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for trait_item in &tcx.trait_items(object.upcast_trait_ref.def_id())[..] {
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if trait_item.def_id() == method_def_id {
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// The item with the ID we were given really ought to be a method.
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assert!(match *trait_item {
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ty::MethodTraitItem(_) => true,
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_ => false
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});
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return entries;
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}
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if let ty::MethodTraitItem(_) = *trait_item {
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entries += 1;
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}
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}
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tcx.sess.bug(&format!("get_vtable_index_of_object_method: {:?} was not found",
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method_def_id));
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}
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pub enum TupleArgumentsFlag { Yes, No }
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pub fn closure_trait_ref_and_return_type<'tcx>(
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tcx: &ty::ctxt<'tcx>,
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fn_trait_def_id: DefId,
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self_ty: Ty<'tcx>,
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sig: &ty::PolyFnSig<'tcx>,
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tuple_arguments: TupleArgumentsFlag)
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-> ty::Binder<(ty::TraitRef<'tcx>, Ty<'tcx>)>
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{
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let arguments_tuple = match tuple_arguments {
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TupleArgumentsFlag::No => sig.0.inputs[0],
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TupleArgumentsFlag::Yes => tcx.mk_tup(sig.0.inputs.to_vec()),
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};
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let trait_substs = Substs::new_trait(vec![arguments_tuple], vec![], self_ty);
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let trait_ref = ty::TraitRef {
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def_id: fn_trait_def_id,
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substs: tcx.mk_substs(trait_substs),
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};
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ty::Binder((trait_ref, sig.0.output.unwrap_or(tcx.mk_nil())))
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}
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