Bubble up opaque <eq> opaque operations instead of picking an order

1 files changed, 21 insertions, 2 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index 3ebf1246a41..f1779451bc5 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -6,6 +6,7 @@ use rustc_infer::infer::DefineOpaqueTypes;
 use rustc_infer::traits::ProjectionCacheKey;
 use rustc_infer::traits::{PolyTraitObligation, SelectionError, TraitEngine};
 use rustc_middle::mir::interpret::ErrorHandled;
+use rustc_middle::traits::DefiningAnchor;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::GenericArgsRef;
@@ -623,9 +624,27 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                     }
                 }
                 ty::PredicateKind::Ambiguous => ProcessResult::Unchanged,
-                ty::PredicateKind::AliasRelate(..) => {
-                    bug!("AliasRelate is only used for new solver")
+                ty::PredicateKind::AliasRelate(..)
+                    if matches!(self.selcx.infcx.defining_use_anchor, DefiningAnchor::Bubble) =>
+                {
+                    ProcessResult::Unchanged
                 }
+                ty::PredicateKind::AliasRelate(a, b, relate) => match relate {
+                    ty::AliasRelationDirection::Equate => match self
+                        .selcx
+                        .infcx
+                        .at(&obligation.cause, obligation.param_env)
+                        .eq(DefineOpaqueTypes::Yes, a, b)
+                    {
+                        Ok(inf_ok) => ProcessResult::Changed(mk_pending(inf_ok.into_obligations())),
+                        Err(_) => ProcessResult::Error(FulfillmentErrorCode::CodeSelectionError(
+                            SelectionError::Unimplemented,
+                        )),
+                    },
+                    ty::AliasRelationDirection::Subtype => {
+                        bug!("AliasRelate with subtyping is only used for new solver")
+                    }
+                },
                 ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
                     match self.selcx.infcx.at(&obligation.cause, obligation.param_env).eq(
                         DefineOpaqueTypes::No,