Infer type context in a type signature

If I have code such as

class Foo f where
    foo :: a -> f a

data Bar f a = Foo f => Bar {bar :: f a}

instance Foo (Bar f) where
    foo a = Bar (foo a)

GHC will demand Foo f => on the instance declaration, even though this can be inferred from the definition of Bar.

I understand why this is happening, but it should not be necessary to repeat information already given. Some code violates DRY dozens of times because of this limitation.