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Fix binder skipping

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This commit is contained in:
Nick Cameron 2015-05-13 14:57:47 +12:00
parent 5d4cce6cec
commit 31bb4ab759
1 changed files with 26 additions and 5 deletions
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31
src/librustc/middle/traits/select.rs
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@ -1369,9 +1369,28 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
fn assemble_candidates_for_unsizing(&mut self,
obligation: &TraitObligation<'tcx>,
candidates: &mut SelectionCandidateSet<'tcx>) {
// It is ok to skip past the higher-ranked binders here because the `match`
// below does not consider regions at all.
let source = self.infcx.shallow_resolve(*obligation.self_ty().skip_binder());
// We currently never consider higher-ranked obligations e.g.
// `for<'a> &'a T: Unsize<Trait+'a>` to be implemented. This is not
// because they are a priori invalid, and we could potentially add support
// for them later, it's just that there isn't really a strong need for it.
// A `T: Unsize<U>` obligation is always used as part of a `T: CoerceUnsize<U>`
// impl, and those are generally applied to concrete types.
//
// That said, one might try to write a fn with a where clause like
// for<'a> Foo<'a, T>: Unsize<Foo<'a, Trait>>
// where the `'a` is kind of orthogonal to the relevant part of the `Unsize`.
// Still, you'd be more likely to write that where clause as
// T: Trait
// so it seems ok if we (conservatively) fail to accept that `Unsize`
// obligation above. Should be possible to extend this in the future.
let self_ty = match ty::no_late_bound_regions(self.tcx(), &obligation.self_ty()) {
Some(t) => t,
None => {
// Don't add any candidates if there are bound regions.
return;
}
};
let source = self.infcx.shallow_resolve(self_ty);
let target = self.infcx.shallow_resolve(obligation.predicate.0.input_types()[0]);
debug!("assemble_candidates_for_unsizing(source={}, target={})",
@ -2403,8 +2422,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
SelectionError<'tcx>> {
let tcx = self.tcx();
// TODO is this skip_binder Ok?
let source = self.infcx.shallow_resolve(*obligation.self_ty().skip_binder());
// assemble_candidates_for_unsizing should ensure there are no late bound
// regions here. See the comment there for more details.
let source = self.infcx.shallow_resolve(
ty::no_late_bound_regions(tcx, &obligation.self_ty()).unwrap());
let target = self.infcx.shallow_resolve(obligation.predicate.0.input_types()[0]);
debug!("confirm_builtin_unsize_candidate(source={}, target={})",