[GHC] #14904: Compiler panic (piResultTy)

[GHC]

#14904: Compiler panic (piResultTy)
-------------------------------------+-------------------------------------
        Reporter:  kcsongor          |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |
      Resolution:  fixed             |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  typecheck/should_fail/T14904a,
                                     |  typecheck/should_fail/T14904b
      Blocked By:                    |             Blocking:
 Related Tickets:  #14873            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by sighingnow):

 For `ASSERT`-enabled ghc-stage2, the testcase T14904b still raises an
 "ASSERT failed!" panic. Not sure if it's worth further fix.

 T14904b.hs:

 {{{#!hs
 import Data.Kind

 type family F f :: Type where
   F ((f :: forall a. g a) :: forall a. g a) = Int
 }}}

 The panic error message:

 {{{
 λ ginplace\bin\ghc-stage2.exe--make T.hs
 [1 of 1] Compiling T14904b          ( T.hs, T.o )
 ghc-stage2.exe: panic! (the 'impossible' happened)
   (GHC version 8.5.20180608 for x86_64-unknown-mingw32):
         ASSERT failed!
   1
   0
   k_aWM[tau:0]
   (g_aWI[sig:0] |> {co_aWV}) a_aX4[tau:0]
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler\utils\Outputable.hs:1161:37 in
 ghc:Outputable
         pprPanic, called at compiler\utils\Outputable.hs:1220:5 in
 ghc:Outputable
         assertPprPanic, called at compiler\\typecheck\\TcMType.hs:745:54
 in ghc:TcMType
 CallStack (from -prof):
   TcRnDriver.tc_rn_src_decls
 (compiler\typecheck\TcRnDriver.hs:(496,4)-(560,7))
   TcRnDriver.tcRnSrcDecls (compiler\typecheck\TcRnDriver.hs:259:25-65)
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14904#comment:7>
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