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Consider negative polarity on trait selection

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Santiago Pastorino 2021-10-13 16:19:29 -03:00
parent 8b0bfb0dcb
commit ab17068662
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1 changed files with 24 additions and 26 deletions
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50
compiler/rustc_trait_selection/src/traits/select/mod.rs
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@ -1127,34 +1127,32 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
}
// Treat negative impls as unimplemented, and reservation impls as ambiguity.
if let ImplCandidate(def_id) = candidate {
match tcx.impl_polarity(def_id) {
ty::ImplPolarity::Negative if !self.allow_negative_impls => {
if let ty::ImplPolarity::Reservation = tcx.impl_polarity(def_id) {
if let Some(intercrate_ambiguity_clauses) = &mut self.intercrate_ambiguity_causes {
let attrs = tcx.get_attrs(def_id);
let attr = tcx.sess.find_by_name(&attrs, sym::rustc_reservation_impl);
let value = attr.and_then(|a| a.value_str());
if let Some(value) = value {
debug!(
"filter_impls: \
reservation impl ambiguity on {:?}",
def_id
);
intercrate_ambiguity_clauses.push(
IntercrateAmbiguityCause::ReservationImpl {
message: value.to_string(),
},
);
}
}
return Ok(None);
}
if !self.allow_negative_impls {
if obligation.predicate.skip_binder().polarity != tcx.impl_polarity(def_id) {
return Err(Unimplemented);
}
ty::ImplPolarity::Reservation => {
if let Some(intercrate_ambiguity_clauses) =
&mut self.intercrate_ambiguity_causes
{
let attrs = tcx.get_attrs(def_id);
let attr = tcx.sess.find_by_name(&attrs, sym::rustc_reservation_impl);
let value = attr.and_then(|a| a.value_str());
if let Some(value) = value {
debug!(
"filter_impls: \
reservation impl ambiguity on {:?}",
def_id
);
intercrate_ambiguity_clauses.push(
IntercrateAmbiguityCause::ReservationImpl {
message: value.to_string(),
},
);
}
}
return Ok(None);
}
_ => {}
};
}
}
Ok(Some(candidate))
}