1 files changed, 16 insertions, 3 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/assembly.rs b/compiler/rustc_trait_selection/src/solve/assembly.rs
index 0f7a0eb337b..856b1c08b72 100644
--- a/compiler/rustc_trait_selection/src/solve/assembly.rs
+++ b/compiler/rustc_trait_selection/src/solve/assembly.rs
@@ -6,6 +6,7 @@ use super::trait_goals::structural_traits::*;
 use super::{EvalCtxt, SolverMode};
 use crate::traits::coherence;
 use itertools::Itertools;
+use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir::def_id::DefId;
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::util::elaborate_predicates;
@@ -489,9 +490,21 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         };
 
         let tcx = self.tcx();
-        for assumption in
-            elaborate_predicates(tcx, bounds.iter().map(|bound| bound.with_self_ty(tcx, self_ty)))
-        {
+        let own_bounds: FxIndexSet<_> =
+            bounds.iter().map(|bound| bound.with_self_ty(tcx, self_ty)).collect();
+        for assumption in elaborate_predicates(tcx, own_bounds.iter().copied()) {
+            // FIXME: Predicates are fully elaborated in the object type's existential bounds
+            // list. We want to only consider these pre-elaborated projections, and not other
+            // projection predicates that we reach by elaborating the principal trait ref,
+            // since that'll cause ambiguity.
+            //
+            // We can remove this when we have implemented intersections in responses.
+            if assumption.to_opt_poly_projection_pred().is_some()
+                && !own_bounds.contains(&assumption)
+            {
+                continue;
+            }
+
             match G::consider_object_bound_candidate(self, goal, assumption) {
                 Ok(result) => {
                     candidates.push(Candidate { source: CandidateSource::BuiltinImpl, result })