[GHC] #14060: TH-reified types can suffer from kind signature oversaturation

[GHC]

#14060: TH-reified types can suffer from kind signature oversaturation
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Template       |           Version:  8.2.1
  Haskell                            |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I ran into this issue when attempting to fix #11785 in `TcSplice`. Here's
 a simple Template Haskell program:

 {{{#!hs
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE TemplateHaskell #-}
 module Bug where

 import Data.Proxy
 import Language.Haskell.TH

 newtype Foo = Foo (Proxy '[False, True, False])

 $(return [])

 main :: IO ()
 main = putStrLn $(reify ''Foo >>= stringE . pprint)
 }}}

 The output of this program is unfortunately noisy:

 {{{
 $ runghc Bug.hs
 newtype Bug.Foo
   = Bug.Foo (Data.Proxy.Proxy ((':) 'GHC.Types.False
                                     ((':) 'GHC.Types.True
                                           ((':) 'GHC.Types.False
                                                 ('[] :: [GHC.Types.Bool])
 :: [GHC.Types.Bool]) :: [GHC.Types.Bool]) :: [GHC.Types.Bool]))
 }}}

 Somehow, we've ended up with four copies of a `[GHC.Types.Bool]` kind
 annotation! It definitely feels like Template Haskell could be more
 conservative here in choosing which types get explicit kind annotations -
 at the most, I'd only expect `'[]` to get one.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14060>
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