Make things work by using the new solver

compiler/rustc_trait_selection/src/solve/assembly/mod.rs

@@ -37,6 +37,8 @@ pub(super) trait GoalKind<'tcx>:
 
     fn trait_ref(self, tcx: TyCtxt<'tcx>) -> ty::TraitRef<'tcx>;
 
+    fn polarity(self) -> ty::ImplPolarity;
+
     fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self;
 
     fn trait_def_id(self, tcx: TyCtxt<'tcx>) -> DefId;

compiler/rustc_trait_selection/src/solve/project_goals/mod.rs

@@ -101,6 +101,10 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
         self.projection_ty.trait_ref(tcx)
     }
 
+    fn polarity(self) -> ty::ImplPolarity {
+        ty::ImplPolarity::Positive
+    }
+
     fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self {
         self.with_self_ty(tcx, self_ty)
     }

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -22,6 +22,10 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
         self.trait_ref
     }
 
+    fn polarity(self) -> ty::ImplPolarity {
+        self.polarity
+    }
+
     fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self {
         self.with_self_ty(tcx, self_ty)
     }