type_parameter_referenced_by_static

Static members can't reference type parameters of the class.

The analyzer produces this diagnostic when a static member references a type parameter that is declared for the class. Type parameters only have meaning for instances of the class.

The following code produces this diagnostic because the static method hasType has a reference to the type parameter T:

class C<T> {
  static bool hasType(Object o) => o is T;
}

If the member can be an instance member, then remove the keyword static:

class C<T> {
  bool hasType(Object o) => o is T;
}

If the member must be a static member, then make the member be generic:

class C<T> {
  static bool hasType<S>(Object o) => o is S;
}

Note, however, that there isn't a relationship between T and S, so this second option changes the semantics from what was likely to be intended.