Open existentials in invariant position

Author: angela-laar

lib/Sema/CSSimplify.cpp

@@ -1568,8 +1568,7 @@ shouldOpenExistentialCallArgument(
       callee, genericSig, genericParam,
       /*treatNonResultCovarianceAsInvariant=*/false,
       /*skipParamIdx=*/paramIdx);
-  if (referenceInfo.selfRef > TypePosition::Covariant ||
-      referenceInfo.assocTypeRef > TypePosition::Covariant)
+  if (referenceInfo.selfRef > TypePosition::Covariant)
     return None;
 
   return std::make_tuple(genericParam, paramTypeVar, argTy, adjustments);