add link to #54105

Author: nikomatsakis

src/librustc_mir/borrow_check/nll/type_check/relate_tys.rs

@@ -695,9 +695,9 @@ impl TypeRelation<'me, 'gcx, 'tcx> for TypeGeneralizer<'me, 'bbcx, 'gcx, 'tcx> {
         // `self.universe` universe, this also serves to enforce the
         // universe scoping rules.
         //
-        // FIXME -- if the ambient variance is bivariant, though, we
-        // may however need to check well-formedness or risk a problem
-        // like #41677 again.
+        // FIXME(#54105) -- if the ambient variance is bivariant,
+        // though, we may however need to check well-formedness or
+        // risk a problem like #41677 again.
 
         let replacement_region_vid = self.type_rel
             .infcx