Reflexive instances for AsType?

[endgame]

There appears to be reflexive instances for AsSubtype and HasType, but not for AsType.

Consider:

data SomethingError = OhNo
  deriving (Generic)

doSomething :: (AsType SomethingError e, MonadError e m) => m ()

In 2.2.1.0 we can write

data AppError = AESomething SomethingError | AEOther Text
  deriving (Generic)

app :: ExceptT AppError IO ()
app = do
  ...
  doSomething
  ...

But

app :: ExceptT SomethingError IO ()
app = do
  ...
  doSomething
  ...

gives an error like The type SomethingError does not contain a constructor whose field is of type SomethingError.

Is there a good reason why we can't add instance AsType a a? Or is there a different way to achieve this kind of behaviour?

Originally posted by @lrworth in https://github.com/kcsongor/generic-lens/issues/85#issuecomment-1056024535