deriving Data.Typeable on phantom newtypes does not report that DeriveDataTypeable is needed

newtype Foo x = Foo deriving (Typeable)

reports the rather cryptic error message:

Can't make a derived instance of Typeable (Foo x)' (even with cunning newtype deriving:) In the newtype declaration for Foo'

When newtype is replaced with data, this much more useful error message is given:

Can't make a derived instance of Typeable (Foo x)' (You need -XDeriveDataTypeable to derive an instance for this class) In the data type declaration for Foo'

Trac metadata

Trac field	Value
Version	6.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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