[GHC] #13738: TypeApplications-related GHC internal error

[GHC]

#13738: TypeApplications-related GHC internal error
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  TypeApplications
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by RyanGlScott):

 BTW, this is pretty much the exact code that GHC emits with `-ddump-deriv`
 if you try to write this `C (Wrap f)` instance with
 `GeneralizedNewtypeDeriving`:

 {{{#!hs
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE PolyKinds #-}
 {-# OPTIONS_GHC -ddump-deriv #-}
 module Works where

 newtype Wrap f a = Wrap (f a) deriving C

 class C f where
   c :: f a
 }}}

 {{{
 GHCi, version 8.3.20170516: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Works            ( Works.hs, interpreted )

 ==================== Derived instances ====================
 Derived class instances:
   instance forall k (f :: k -> *).
            Works.C f =>
            Works.C (Works.Wrap f) where
     Works.c
       = GHC.Prim.coerce
           @(forall (a_a1tD :: k_a1uE). f_a1tE a_a1tD)
           @(forall (a_a1tD :: k_a1uE). Works.Wrap f_a1tE a_a1tD)
           Works.c


 Derived type family instances:
 }}}

 This reveals a pretty-printing bug, as the explicitly quantified kind
 variable `k` referred to by a different name `k_a1uE` later.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13738#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler