self ty infer ambiguity: add proof tree cand

Author: lcnr

compiler/rustc_trait_selection/src/solve/assembly/mod.rs

@@ -263,7 +263,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
     ) -> Vec<Candidate<'tcx>> {
         debug_assert_eq!(goal, self.resolve_vars_if_possible(goal));
         if let Some(ambig) = self.assemble_self_ty_infer_ambiguity_response(goal) {
-            return ambig;
+            return vec![ambig];
         }
 
         let mut candidates = self.assemble_candidates_via_self_ty(goal, 0);
@@ -288,15 +288,20 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
     fn assemble_self_ty_infer_ambiguity_response<G: GoalKind<'tcx>>(
         &mut self,
         goal: Goal<'tcx, G>,
-    ) -> Option<Vec<Candidate<'tcx>>> {
-        goal.predicate.self_ty().is_ty_var().then(|| {
-            vec![Candidate {
-                source: CandidateSource::BuiltinImpl(BuiltinImplSource::Misc),
-                result: self
-                    .evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
-                    .unwrap(),
-            }]
-        })
+    ) -> Option<Candidate<'tcx>> {
+        if goal.predicate.self_ty().is_ty_var() {
+            debug!("adding self_ty_infer_ambiguity_response");
+            let source = CandidateSource::BuiltinImpl(BuiltinImplSource::Misc);
+            let result = self
+                .evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
+                .unwrap();
+            let mut dummy_probe = self.inspect.new_probe();
+            dummy_probe.probe_kind(ProbeKind::TraitCandidate { source, result: Ok(result) });
+            self.inspect.finish_probe(dummy_probe);
+            Some(Candidate { source, result })
+        } else {
+            None
+        }
     }
 
     /// Assemble candidates which apply to the self type. This only looks at candidate which
@@ -310,7 +315,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
     ) -> Vec<Candidate<'tcx>> {
         debug_assert_eq!(goal, self.resolve_vars_if_possible(goal));
         if let Some(ambig) = self.assemble_self_ty_infer_ambiguity_response(goal) {
-            return ambig;
+            return vec![ambig];
         }
 
         let mut candidates = Vec::new();

tests/ui/impl-trait/auto-trait-coherence.next.stderr

@@ -6,8 +6,6 @@ LL | impl<T: Send> AnotherTrait for T {}
 ...
 LL | impl AnotherTrait for D<OpaqueType> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<OpaqueType>`
-   |
-   = note: upstream crates may add a new impl of trait `std::marker::Send` for type `OpaqueType` in future versions
 
 error: aborting due to previous error
 

tests/ui/traits/new-solver/coherence/trait_ref_is_knowable-norm-overflow.stderr

@@ -6,9 +6,6 @@ LL | impl<T: Copy> Trait for T {}
 LL | struct LocalTy;
 LL | impl Trait for <LocalTy as Overflow>::Assoc {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `<LocalTy as Overflow>::Assoc`
-   |
-   = note: downstream crates may implement trait `std::marker::Sized` for type `<LocalTy as Overflow>::Assoc`
-   = note: downstream crates may implement trait `std::marker::Copy` for type `<LocalTy as Overflow>::Assoc`
 
 error: aborting due to previous error