Prefer lower TraitUpcasting candidates

2025-01-14 17:54:53 +00:00
parent 2ae9916816
commit bf545ce2fe
6 changed files with 54 additions and 6 deletions
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -741,12 +741,14 @@ where
                a_data.principal(),
            ));
        } else if let Some(a_principal) = a_data.principal() {
-            for new_a_principal in
-                elaborate::supertraits(self.cx(), a_principal.with_self_ty(cx, a_ty)).skip(1)
+            for (idx, new_a_principal) in
+                elaborate::supertraits(self.cx(), a_principal.with_self_ty(cx, a_ty))
+                    .enumerate()
+                    .skip(1)
            {
                responses.extend(self.consider_builtin_upcast_to_principal(
                    goal,
-                    CandidateSource::BuiltinImpl(BuiltinImplSource::TraitUpcasting),
+                    CandidateSource::BuiltinImpl(BuiltinImplSource::TraitUpcasting(idx)),
                    a_data,
                    a_region,
                    b_data,