conflicting_type_variable_and_container

'{0}' can't be used to name both a type parameter and the class in which the type parameter is defined.

'{0}' can't be used to name both a type parameter and the enum in which the type parameter is defined.

'{0}' can't be used to name both a type parameter and the extension in which the type parameter is defined.

'{0}' can't be used to name both a type parameter and the extension type in which the type parameter is defined.

'{0}' can't be used to name both a type parameter and the mixin in which the type parameter is defined.

The analyzer produces this diagnostic when a class, mixin, or extension declaration declares a type parameter with the same name as the class, mixin, or extension that declares it.

The following code produces this diagnostic because the type parameter C has the same name as the class C of which it's a part:

class C<C> {}

Rename either the type parameter, or the class, mixin, or extension:

class C<T> {}