wrong_number_of_parameters_for_setter

Setters must declare exactly one required positional parameter.

The analyzer produces this diagnostic when a setter is found that doesn't declare exactly one required positional parameter.

The following code produces this diagnostic because the setter s declares two required parameters:

class C {
  set s(int x, int y) {}
}

The following code produces this diagnostic because the setter s declares one optional parameter:

class C {
  set s([int? x]) {}
}

Change the declaration so that there's exactly one required positional parameter:

class C {
  set s(int x) {}
}