Derived DataKinds Typeable instance collision leads to SafeHaskell violation
The derived Typeable
instances for a kind (with DataKinds
) is equal to the
instance of a type with the same name:
λ> data T = T
λ> typeRep (Proxy :: Proxy T) == typeRep (Proxy :: Proxy 'T)
True
This can be used to violate SafeHaskell
easily:
{-# LANGUAGE AutoDeriveTypeable, DataKinds, TypeFamilies, RankNTypes #-}
module Unsafe where
import Data.Typeable
data T = T
data family F p
newtype instance F (Proxy T) = ID (forall a. a -> a)
newtype instance F (Proxy 'T) = UC (forall a b. a -> b)
uc :: a -> b
uc = case cast (ID id) of Just (UC f) -> f
$ ghc -XSafe Unsafe.hs -e "uc 'a' :: Int"
97
Trac metadata
Trac field | Value |
---|---|
Version | 7.8.4 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |