deprecated_subtype_of_function

Extending 'Function' is deprecated.

Implementing 'Function' has no effect.

Mixing in 'Function' is deprecated.

The analyzer produces this diagnostic when the class Function is used in either the extends, implements, or with clause of a class or mixin. Using the class Function in this way has no semantic value, so it's effectively dead code.

The following code produces this diagnostic because Function is used as the superclass of F:

class F extends Function {}

Remove the class Function from whichever clause it's in, and remove the whole clause if Function is the only type in the clause:

class F {}