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HEAD: `KnownNat` does not imply `Typeable` any more

As Iavor confirmed (https://mail.haskell.org/pipermail/ghc-devs/2015-April/008885.html) there is a regression on HEAD relative to ghc-7.11.20150215. Here is a reproduction snippet:

{-# LANGUAGE AutoDeriveTypeable, GADTs, DataKinds, KindSignatures, StandaloneDeriving #-}

import GHC.TypeLits
import Data.Typeable

data Foo (n :: Nat) where
  Hey :: KnownNat n => Foo n

deriving instance Show (Foo n)

data T t where
  T :: (Show t, Typeable t) => t -> T t

deriving instance Show (T n)

With ghci-7.11.20150407 I now see more constraints

*Main> :t T Hey
T Hey :: (Typeable n, KnownNat n) => T (Foo n)

OTOH ghci-7.11.20150215 only wanted KnownNat:

*Main> :t T Hey
T Hey :: KnownNat n => T (Foo n)
Trac metadata
Trac field Value
Version 7.11
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture
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