deriving Generic does not work with TypeLits

{-# LANGUAGE DataKinds, KindSignatures #-}
{-# LANGUAGE DeriveGeneric #-}

import GHC.TypeLits
import GHC.Generics

data F (a :: Symbol)
data X = X (F "hello") deriving Generic

Trying to derive Generics instance for simple datatype with Symbol inside but GHC complains:

  Can't make a derived instance of `Generic X':
     X must not have unlifted or polymorphic arguments
   In the data declaration for `X'

I found that this could be fixed by adding single line to isTauTy:

--- a/compiler/typecheck/TcType.lhs
+++ b/compiler/typecheck/TcType.lhs
@@ -899,6 +899,7 @@ mkTcEqPred ty1 ty2
 isTauTy :: Type -> Bool
 isTauTy ty | Just ty' <- tcView ty = isTauTy ty'
 isTauTy (TyVarTy _)      = True
+isTauTy (LitTy _)        = True
 isTauTy (TyConApp tc tys) = all isTauTy tys && isTauTyCon tc
 isTauTy (AppTy a b)      = isTauTy a && isTauTy b
 isTauTy (FunTy a b)      = isTauTy a && isTauTy b

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	ValidProgramRejected
Priority	normal
Resolution	Unresolved
Component	Compiler
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