diff options
| -rw-r--r-- | src/librustc_typeck/check/closure.rs | 37 |
1 files changed, 25 insertions, 12 deletions
diff --git a/src/librustc_typeck/check/closure.rs b/src/librustc_typeck/check/closure.rs index b8def243635..162555cd3ce 100644 --- a/src/librustc_typeck/check/closure.rs +++ b/src/librustc_typeck/check/closure.rs @@ -698,20 +698,32 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { /// Given a projection like /// - /// `<_ as Future>::Output = T` + /// `<X as Future>::Output = T` /// - /// returns `Some(T)`. If the projection is for some other trait, - /// returns `None`. + /// where `X` is some type that has no late-bound regions, returns + /// `Some(T)`. If the projection is for some other trait, returns + /// `None`. fn deduce_future_output_from_projection( &self, cause_span: Span, - projection: &ty::PolyProjectionPredicate<'tcx>, + predicate: &ty::PolyProjectionPredicate<'tcx>, ) -> Option<Ty<'tcx>> { - debug!("deduce_future_output_from_projection(projection={:?})", projection); + debug!("deduce_future_output_from_projection(predicate={:?})", predicate); + + // We do not expect any bound regions in our predicate, so + // skip past the bound vars. + let predicate = match predicate.no_bound_vars() { + Some(p) => p, + None => { + debug!("deduce_future_output_from_projection: has late-bound regions"); + return None; + } + }; - let trait_ref = projection.to_poly_trait_ref(self.tcx); + // Check that this is a projection from the `Future` trait. + let trait_ref = predicate.projection_ty.trait_ref(self.tcx); let future_trait = self.tcx.lang_items().future_trait().unwrap(); - if trait_ref.def_id() != future_trait { + if trait_ref.def_id != future_trait { debug!("deduce_future_output_from_projection: not a future"); return None; } @@ -719,18 +731,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { // The `Future` trait has only one associted item, `Output`, // so check that this is what we see. let output_assoc_item = self.tcx.associated_items(future_trait).nth(0).unwrap().def_id; - if output_assoc_item != projection.projection_def_id() { + if output_assoc_item != predicate.projection_ty.item_def_id { span_bug!( cause_span, "projecting associated item `{:?}` from future, which is not Output `{:?}`", - projection.projection_def_id(), + predicate.projection_ty.item_def_id, output_assoc_item, ); } - // Extract the type from the projection. - let output_ty = projection.skip_binder().ty; - let output_ty = self.resolve_vars_if_possible(&output_ty); + // Extract the type from the projection. Note that there can + // be no bound variables in this type because the "self type" + // does not have any regions in it. + let output_ty = self.resolve_vars_if_possible(&predicate.ty); debug!("deduce_future_output_from_projection: output_ty={:?}", output_ty); Some(output_ty) } |