Re: [GHC] #15076: Typed hole with higher-rank kind causes GHC to panic (No skolem info) (was: Typed hole causes GHC to panic (No skolem info))

22 Apr 2018

      #15076: Typed hole with higher-rank kind causes GHC to panic (No skolem info)
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |             Keywords:  TypedHoles,
      Resolution:                    |  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14040            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by RyanGlScott:

Old description:
...
Spun out from https://ghc.haskell.org/trac/ghc/ticket/14040#comment:2,
which was different enough from the original program in #14040 to warrant
its own ticket. The following program panics on every version of GHC from
8.0.2 onward:
{{{#!hs
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeInType #-}
module Bug where
import Data.Kind
import Data.Proxy
newtype S (f :: k1 -> k2) = MkS (Proxy f)
foo :: forall (a :: Type)
              (f :: forall (x :: a). Proxy x -> Type).
       S f -> ()
foo (MkS (sF :: _)) = ()
}}}
{{{
$ ~/Software/ghc/inplace/bin/ghc-stage2 --interactive Bug.hs
GHCi, version 8.5.20180420: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
[1 of 1] Compiling Bug              ( Bug.hs, interpreted )
Bug.hs:14:17: error:ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.5.20180420 for x86_64-unknown-linux):
        No skolem info:
  [a_a1Ca[sk:1]]
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/utils/Outputable.hs:1162:37 in
ghc:Outputable
        pprPanic, called at compiler/typecheck/TcErrors.hs:3224:5 in
ghc:TcErrors
}}}
New description:

 Spun out from https://ghc.haskell.org/trac/ghc/ticket/14040#comment:2,
 which was different enough from the original program in #14040 to warrant
 its own ticket. The following program panics on every version of GHC from
 8.0.2 onward:

 {{{#!hs
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeInType #-}
 module Bug where

 import Data.Kind
 import Data.Proxy

 foo :: forall (a :: Type)
               (f :: forall (x :: a). Proxy x -> Type).
        Proxy f -> ()
 foo (_ :: _) = ()
 }}}
 {{{
 $ ~/Software/ghc/inplace/bin/ghc-stage2 Bug.hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )

 Bug.hs:12:11: error:ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.5.20180420 for x86_64-unknown-linux):
         No skolem info:
   [a_aZo[sk:1]]
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1162:37 in
 ghc:Outputable
         pprPanic, called at compiler/typecheck/TcErrors.hs:3224:5 in
 ghc:TcErrors
 }}}

--

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15076#comment:3
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler