duplicate_field_formal_parameter

The field '{0}' can't be initialized by multiple parameters in the same constructor.

The analyzer produces this diagnostic when there's more than one initializing formal parameter for the same field in a constructor's parameter list. It isn't useful to assign a value that will immediately be overwritten.

The following code produces this diagnostic because this.f appears twice in the parameter list:

class C {
  int f;

  C(this.f, this.f) {}
}

Remove one of the initializing formal parameters:

class C {
  int f;

  C(this.f) {}
}