Don't match any projection predicates when the obligation has inference types or consts in GAT substs

2 files changed, 12 insertions, 2 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 6634f3e364d..9a7d06ef640 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -2470,8 +2470,8 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 let projection_ty = ty::ProjectionTy {
                     // `T`
                     substs: self.tcx.mk_substs_trait(
-                        trait_pred.self_ty().skip_binder(),
-                        self.fresh_substs_for_item(span, item_def_id),
+                        trait_ref.self_ty().skip_binder(),
+                        &self.fresh_substs_for_item(span, item_def_id)[1..],
                     ),
                     // `Future::Output`
                     item_def_id,
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 47427395b93..562535b0fea 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1521,6 +1521,16 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             infer_predicate.projection_ty
         };
 
+        // If the obligation contains any inference types or consts in associated
+        // type substs, then we don't match any projection candidates against it.
+        // This isn't really correct, but otherwise we can end up in a case where
+        // we constrain inference variables by selecting a single predicate, when
+        // we need to stay general. See issue #91762.
+        let (_, predicate_own_substs) =
+            obligation.predicate.trait_ref_and_own_substs(self.infcx.tcx);
+        if predicate_own_substs.iter().any(|g| g.has_infer_types_or_consts()) {
+            return false;
+        }
         self.infcx
             .at(&obligation.cause, obligation.param_env)
             .sup(obligation.predicate, infer_projection)