"deriving" seems to ignore class context for a type family

class Foo a where
  data Bar a :: *

class (Show (Bar a)) => Qux a
data (Qux a) => Xyzzy a = Xyzzy (Bar a) deriving Show

Here I get the following error:

    No instance for (Show (Bar a))
      arising from the 'deriving' clause of a data type declaration
    Possible fix:
      add an instance declaration for (Show (Bar a))
      or use a standalone 'deriving instance' declaration,
           so you can specify the instance context yourself
    When deriving the instance for (Show (Xyzzy a))

Curiously, I get the same error even if I add ", Show (Bar a)" to the context of "Xyzzy".

Trac metadata

Trac field	Value
Version	7.0.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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