invalid_deprecated_extend_annotation

The annotation '@Deprecated.extend' can only be applied to extendable classes.

The analyzer produces this diagnostic when anything other than an extendable class is annotated with Deprecated.extend. An extendable class is a class not declared with the interface, final, or sealed keywords, and with at least one public generative constructor.

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

@Deprecated.extend()
sealed class C {}

Remove the annotation:

sealed class C {}