pub fn trait_ref_is_knowable<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::TraitRef<'tcx>,
-) -> Option<Conflict> {
+) -> Result<(), Conflict> {
debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref);
if orphan_check_trait_ref(tcx, trait_ref, InCrate::Remote).is_ok() {
// A downstream or cousin crate is allowed to implement some
// substitution of this trait-ref.
- return Some(Conflict::Downstream);
+ return Err(Conflict::Downstream);
}
if trait_ref_is_local_or_fundamental(tcx, trait_ref) {
// allowed to implement a substitution of this trait ref, which
// means impls could only come from dependencies of this crate,
// which we already know about.
- return None;
+ return Ok(());
}
// This is a remote non-fundamental trait, so if another crate
// we are an owner.
if orphan_check_trait_ref(tcx, trait_ref, InCrate::Local).is_ok() {
debug!("trait_ref_is_knowable: orphan check passed");
- None
+ Ok(())
} else {
debug!("trait_ref_is_knowable: nonlocal, nonfundamental, unowned");
- Some(Conflict::Upstream)
+ Err(Conflict::Upstream)
}
}
&mut self,
stack: &TraitObligationStack<'o, 'tcx>,
) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
- if let Some(conflict) = self.is_knowable(stack) {
+ if let Err(conflict) = self.is_knowable(stack) {
debug!("coherence stage: not knowable");
if self.intercrate_ambiguity_causes.is_some() {
debug!("evaluate_stack: intercrate_ambiguity_causes is some");
Ok(Some(candidate))
}
- fn is_knowable<'o>(&mut self, stack: &TraitObligationStack<'o, 'tcx>) -> Option<Conflict> {
+ fn is_knowable<'o>(&mut self, stack: &TraitObligationStack<'o, 'tcx>) -> Result<(), Conflict> {
debug!("is_knowable(intercrate={:?})", self.intercrate);
if !self.intercrate || stack.obligation.polarity() == ty::ImplPolarity::Negative {
- return None;
+ return Ok(());
}
let obligation = &stack.obligation;