2 files changed, 28 insertions, 1 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs
index 6fb788e296f..74dfbdddbab 100644
--- a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs
+++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs
@@ -837,7 +837,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         }
     }
 
-    pub(super) fn can_define_opaque_ty(&mut self, def_id: LocalDefId) -> bool {
+    pub(super) fn can_define_opaque_ty(&self, def_id: LocalDefId) -> bool {
         self.infcx.opaque_type_origin(def_id).is_some()
     }
 
diff --git a/compiler/rustc_trait_selection/src/solve/trait_goals.rs b/compiler/rustc_trait_selection/src/solve/trait_goals.rs
index 7ff47295e7c..cd68626bed1 100644
--- a/compiler/rustc_trait_selection/src/solve/trait_goals.rs
+++ b/compiler/rustc_trait_selection/src/solve/trait_goals.rs
@@ -7,6 +7,7 @@ use rustc_hir::{LangItem, Movability};
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::util::supertraits;
 use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, QueryResult};
+use rustc_middle::traits::Reveal;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams, TreatProjections};
 use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
 use rustc_middle::ty::{TraitPredicate, TypeVisitableExt};
@@ -118,6 +119,32 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
             return result;
         }
 
+        // Don't call `type_of` on a local TAIT that's in the defining scope,
+        // since that may require calling `typeck` on the same item we're
+        // currently type checking, which will result in a fatal cycle that
+        // ideally we want to avoid, since we can make progress on this goal
+        // via an alias bound or a locally-inferred hidden type instead.
+        //
+        // Also, don't call `type_of` on a TAIT in `Reveal::All` mode, since
+        // we already normalize the self type in
+        // `assemble_candidates_after_normalizing_self_ty`, and we'd
+        // just be registering an identical candidate here.
+        //
+        // Returning `Err(NoSolution)` here is ok in `SolverMode::Coherence`
+        // since we'll always be registering an ambiguous candidate in
+        // `assemble_candidates_after_normalizing_self_ty` due to normalizing
+        // the TAIT.
+        if let ty::Alias(ty::Opaque, opaque_ty) = goal.predicate.self_ty().kind() {
+            if matches!(goal.param_env.reveal(), Reveal::All)
+                || opaque_ty
+                    .def_id
+                    .as_local()
+                    .is_some_and(|def_id| ecx.can_define_opaque_ty(def_id))
+            {
+                return Err(NoSolution);
+            }
+        }
+
         ecx.probe_and_evaluate_goal_for_constituent_tys(
             goal,
             structural_traits::instantiate_constituent_tys_for_auto_trait,