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Remove unification despite ambiguity in projection #33555

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Merged
merged 1 commit into from
May 14, 2016
Merged

Remove unification despite ambiguity in projection #33555

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58 changes: 1 addition & 57 deletions src/librustc/traits/project.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -218,10 +218,7 @@ fn project_and_unify_type<'cx, 'gcx, 'tcx>(
obligation.cause.clone(),
obligation.recursion_depth) {
Some(n) => n,
None => {
consider_unification_despite_ambiguity(selcx, obligation);
return Ok(None);
}
None => return Ok(None),
};

debug!("project_and_unify_type: normalized_ty={:?} obligations={:?}",
Expand All @@ -240,59 +237,6 @@ fn project_and_unify_type<'cx, 'gcx, 'tcx>(
}
}

fn consider_unification_despite_ambiguity<'cx, 'gcx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'gcx, 'tcx>,
obligation: &ProjectionObligation<'tcx>)
{
debug!("consider_unification_despite_ambiguity(obligation={:?})",
obligation);

let def_id = obligation.predicate.projection_ty.trait_ref.def_id;
match selcx.tcx().lang_items.fn_trait_kind(def_id) {
Some(_) => { }
None => { return; }
}

let infcx = selcx.infcx();
let self_ty = obligation.predicate.projection_ty.trait_ref.self_ty();
let self_ty = infcx.shallow_resolve(self_ty);
debug!("consider_unification_despite_ambiguity: self_ty.sty={:?}",
self_ty.sty);
match self_ty.sty {
ty::TyClosure(closure_def_id, substs) => {
let closure_typer = selcx.closure_typer();
let closure_type = closure_typer.closure_type(closure_def_id, substs);
let ty::Binder((_, ret_type)) =
infcx.tcx.closure_trait_ref_and_return_type(def_id,
self_ty,
&closure_type.sig,
util::TupleArgumentsFlag::No);
// We don't have to normalize the return type here - this is only
// reached for TyClosure: Fn inputs where the closure kind is
// still unknown, which should only occur in typeck where the
// closure type is already normalized.
let (ret_type, _) =
infcx.replace_late_bound_regions_with_fresh_var(
obligation.cause.span,
infer::AssocTypeProjection(obligation.predicate.projection_ty.item_name),
&ty::Binder(ret_type));

debug!("consider_unification_despite_ambiguity: ret_type={:?}",
ret_type);
let origin = TypeOrigin::RelateOutputImplTypes(obligation.cause.span);
let obligation_ty = obligation.predicate.ty;
match infcx.eq_types(true, origin, obligation_ty, ret_type) {
Ok(InferOk { obligations, .. }) => {
// FIXME(#32730) propagate obligations
assert!(obligations.is_empty());
}
Err(_) => { /* ignore errors */ }
}
}
_ => { }
}
}

/// Normalizes any associated type projections in `value`, replacing
/// them with a fully resolved type where possible. The return value
/// combines the normalized result and any additional obligations that
Expand Down