panic.hs

type I = Data.Vinyl.Functor.Identity
 (Identity (3 :: Int) :& Identity "foo" :& RNil) ^. rlens (Proxy @Int)

<interactive>:100:2: error:
    Ambiguous occurrence ‘Identity’
    It could refer to either ‘Control.Lens.Identity’,
                             imported from ‘Control.Lens’
                             (and originally defined in ‘Data.Functor.Identity’)
                          or ‘Data.Vinyl.Functor.Identity’,
                             imported from ‘Data.Vinyl.Functor’

<interactive>:100:25: error:
    Ambiguous occurrence ‘Identity’
    It could refer to either ‘Control.Lens.Identity’,
                             imported from ‘Control.Lens’
                             (and originally defined in ‘Data.Functor.Identity’)
                          or ‘Data.Vinyl.Functor.Identity’,
                             imported from ‘Data.Vinyl.Functor’
 (I (3 :: Int) :& I "foo" :& RNil) ^. rlens (Proxy @Int)
intero: panic! (the 'impossible' happened)
  (GHC version 8.0.2 for x86_64-apple-darwin):
	initTc: unsolved constraints
  WC {wc_insol =
        [W] I_a53fT :: t_a53fS[tau:1] (CHoleCan: I)
        [W] I_a53g9 :: t_a53g8[tau:1] (CHoleCan: I)
        [W] Proxy_a53gv :: t_a53gu[tau:1] (CHoleCan: Proxy)
        [W] I_a53gZ :: t_a53gY[tau:1] (CHoleCan: I)
        [W] I_a53hf :: t_a53he[tau:1] (CHoleCan: I)
        [W] Proxy_a53hB :: t_a53hA[tau:1] (CHoleCan: Proxy)}

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug