Rollup merge of #106309 - compiler-errors:prefer-non-err-candidates, r=oli-obk

Prefer non-`[type error]` candidates during selection

Fixes #102130
Fixes #106351

r? types

note: Alternatively we could filter out error where-clauses during param-env construction? But we still need to filter out impls with errors during `match_impl`, I think.

2 files changed, 5 insertions, 1 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index c54d901e9b1..170c1673dbd 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -174,7 +174,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .param_env
             .caller_bounds()
             .iter()
-            .filter_map(|o| o.to_opt_poly_trait_pred());
+            .filter_map(|p| p.to_opt_poly_trait_pred())
+            .filter(|p| !p.references_error());
 
         // Micro-optimization: filter out predicates relating to different traits.
         let matching_bounds =
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 3f14491f803..2615e262282 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -2377,6 +2377,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let impl_substs = self.infcx.fresh_substs_for_item(obligation.cause.span, impl_def_id);
 
         let impl_trait_ref = impl_trait_ref.subst(self.tcx(), impl_substs);
+        if impl_trait_ref.references_error() {
+            return Err(());
+        }
 
         debug!(?impl_trait_ref);