no_generative_constructors_in_superclass

The class '{0}' can't extend '{1}' because '{1}' only has factory constructors (no generative constructors), and '{0}' has at least one generative constructor.

The analyzer produces this diagnostic when a class that has at least one generative constructor (whether explicit or implicit) has a superclass that doesn't have any generative constructors. Every generative constructor, except the one defined in Object, invokes, either explicitly or implicitly, one of the generative constructors from its superclass.

The following code produces this diagnostic because the class B has an implicit generative constructor that can't invoke a generative constructor from A because A doesn't have any generative constructors:

class A {
  factory A.none() => throw '';
}

class B extends A {}

If the superclass should have a generative constructor, then add one:

class A {
  A();
  factory A.none() => throw '';
}

class B extends A {}

If the subclass shouldn't have a generative constructor, then remove it by adding a factory constructor:

class A {
  factory A.none() => throw '';
}

class B extends A {
  factory B.none() => throw '';
}

If the subclass must have a generative constructor but the superclass can't have one, then implement the superclass instead:

class A {
  factory A.none() => throw '';
}

class B implements A {}