[GHC] #14055: Panic on type error inside a type-level newtype

[GHC]

#14055: Panic on type error inside a type-level newtype
-------------------------------------+-------------------------------------
        Reporter:  luqui             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |
      Resolution:                    |             Keywords:
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:                    |
-------------------------------------+-------------------------------------
Changes (by RyanGlScott):

 * os:  MacOS X => Unknown/Multiple
 * component:  Compiler => Compiler (Type checker)
 * architecture:  x86_64 (amd64) => Unknown/Multiple


Comment:

 This doesn't panic on GHC HEAD:

 {{{
 $ ~/Software/ghc3/inplace/bin/ghc-stage2 --interactive Bug.hs
 GHCi, version 8.3.20170729: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Main             ( Bug.hs, interpreted )

 Bug.hs:6:18: error:
     • Expected kind ‘() -> X’, but ‘t -> ()’ has kind ‘*’
     • In the first argument of ‘RollX’, namely ‘(t -> ())’
       In the type ‘RollX (t -> ())’
       In the type family declaration for ‘F’
   |
 6 |     F t = RollX (t -> ())
   |                  ^^^^^^^
 }}}

 8e15e3d370e9c253ae0dbb330e25b72cb00cdb76 likely fixed this. I'll add a
 regression test.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14055#comment:2>
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