invalid_deprecated_implement_annotation

The annotation '@Deprecated.implement' can only be applied to implementable classes.

The analyzer produces this diagnostic when anything other than an implementable class or mixin is annotated with Deprecated.implement. An implementable class or mixin is one not declared with the base, final, or sealed keywords.

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

@Deprecated.implement()
sealed class C {}

Remove the annotation:

sealed class C {}