mixin_class_declares_non_trivial_generative_constructor

The mixin class '{0}' can't declare a non-trivial generative constructor.

The analyzer produces this diagnostic when a mixin class declares a non-trivial generative constructor. Trivial constructors are allowed, but non-trivial ones (those with parameters, bodies, or initializers) aren't.

The following code produces this diagnostic because the mixin class A defines a generative constructor with a body:

mixin class A {
  A() {}
}

If you can remove the body or parameters of the constructor to make it trivial, then do so:

mixin class A {
  A(); // Trivial constructor
}

If the constructor can't be made trivial, then convert the mixin class to a regular class and extend or implement it, or separate the mixin capability:

class A {
  A() {}
}
​
mixin class AM { // A separate mixin for mixing in behavior
}