unqualified_reference_to_static_member_of_extended_type

Static members from the extended type or one of its superclasses must be qualified by the name of the defining type.

The analyzer produces this diagnostic when an undefined name is found, and the name is the same as a static member of the extended type or one of its superclasses.

The following code produces this diagnostic because m is a static member of the extended type C:

class C {
  static void m() {}
}
​
extension E on C {
  void f() {
    m();
  }
}

If you're trying to reference a static member that's declared outside the extension, then add the name of the class or extension before the reference to the member:

class C {
  static void m() {}
}
​
extension E on C {
  void f() {
    C.m();
  }
}

If you're referencing a member that isn't declared yet, add a declaration:

class C {
  static void m() {}
}
​
extension E on C {
  void f() {
    m();
  }
​
  void m() {}
}