Fix.

source/slang/slang-check-overload.cpp

@@ -2266,6 +2266,7 @@ namespace Slang
  for (auto& arg : expr->arguments)
  {
  arg = maybeOpenRef(arg);
+ arg = maybeOpenExistential(arg);
  }
 
  context.originalExpr = expr;
@@ -2394,6 +2395,10 @@ namespace Slang
  // the user the most help we can.
  if (shouldAddToCache)
  typeCheckingCache->resolvedOperatorOverloadCache[key] = *context.bestCandidate;
+
+ // Now that we have resolved the overload candidate, we need to undo an `openExistential`
+ // operation that was applied to `out` arguments.
+ //
  auto funcType = context.bestCandidate->funcType;
  ShortList<ParameterDirection> paramDirections;
  if (funcType)
@@ -2421,12 +2426,13 @@ namespace Slang
  case kParameterDirection_InOut:
  case kParameterDirection_Ref:
  case kParameterDirection_ConstRef:
- continue;
- default:
  break;
+ default:
+ continue;
  }
  }
- arg = maybeOpenExistential(arg);
+ if (auto extractExistentialExpr = as<ExtractExistentialValueExpr>(arg))
+ arg = extractExistentialExpr->originalExpr;
  }
  return CompleteOverloadCandidate(context, *context.bestCandidate);
  }