expected_two_map_pattern_type_arguments

Map patterns require two type arguments or none, but {0} found.

The analyzer produces this diagnostic when a map pattern has either one type argument or more than two type arguments. Map patterns can have either two type arguments or zero type arguments, but can't have any other number.

The following code produces this diagnostic because the map pattern (<int>{}) has one type argument:

void f(Object x) {
  if (x case <int>{0: _}) {}
}

Add or remove type arguments until there are two, or none:

void f(Object x) {
  if (x case <int, int>{0: _}) {}
}