invalid_deprecated_subclass_annotation

The annotation '@Deprecated.subclass' can only be applied to subclassable classes and mixins.

The analyzer produces this diagnostic when anything other than a subclassable class or mixin is annotated with Deprecated.subclass. A subclassable class is a class not declared with the final or sealed keywords. A subclassable mixin is a mixin not declared with the base keyword.

The following code produces this diagnostic because the annotation is on a sealed class:

@Deprecated.subclass()
sealed class C {}

Remove the annotation:

sealed class C {}