Pattern: Missing use of mixin
Issue: -
Dart 2.1 introduced a new syntax for mixins that provides a safe way for a mixin
to invoke inherited members using super. The new style of mixins should always
be used for types that are to be mixed in. As a result, this lint will flag any
uses of a class in a with clause.
Example of incorrect code:
class A {}
class B extends Object with A {}OK:
mixin M {}
class C with M {}