[GHC] #13658: Assertion failure on HEAD: "optCoercion changed types!"

[GHC]

#13658: Assertion failure on HEAD: "optCoercion changed types!"
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by slyfox):

 This should be self-contained example. You'll need a debugging compiler to
 build it.
 I'm not sure I've preserved kind structure of original module as core-lint
 detects
 all sorts of problems in this program.

 But the error is still the same. I was not able to remove foldl/foldr: the
 error goes away.

 {{{#!hs
 -- Bug.hs:
 {-# LANGUAGE TypeInType #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE RankNTypes #-}

 {- # OPTIONS_GHC -Werror #-}
 {-# OPTIONS_GHC -g -O2 #-}

 module Bug (bug) where

 import Unsafe.Coerce (unsafeCoerce)

 undefined :: a
 undefined = undefined

 prelude_id :: a -> a
 prelude_id x = x

 prelude_foldl :: forall a b. (b -> a -> b) -> b -> [a] -> b
 prelude_foldl k z0 xs =
   prelude_foldr (\v fn -> (\z -> fn (k z v))) prelude_id xs z0

 prelude_foldr :: (a -> b -> b) -> b -> [a] -> b
 prelude_foldr f z = go
           where
             go []     = z
             go (y:ys) = y `f` go ys

 data TypeRep (a :: k) where
     TrTyCon :: TypeRep (a :: k)
     TrApp   :: forall k1 k2 (a :: k1 -> k2) (b :: k1). TypeRep (a b)

 data SomeTypeRep where
     SomeTypeRep :: forall k (a :: k). TypeRep a -> SomeTypeRep

 mkTrApp :: forall k1 k2 (a :: k1 -> k2) (b :: k1).
            TypeRep (a :: k1 -> k2)
         -> TypeRep (a b)
 mkTrApp TrTyCon = undefined
 mkTrApp TrApp   = undefined

 bug :: [a] -> SomeTypeRep
 bug args = prelude_foldl applyTy tycon_app args
   where tycon_app = SomeTypeRep TrTyCon
         applyTy :: SomeTypeRep -> a -> SomeTypeRep
         applyTy (SomeTypeRep acc) _unused
           = SomeTypeRep (mkTrApp (unsafeCoerce acc))
 }}}

 {{{
 $ ../"inplace/bin/ghc-stage1" -hisuf hi -osuf  o -hcsuf hc -static  -H32m
 -O -g -dcore-lint -DDEBUG -Wall       -this-unit-id base-4.10.0.0 -hide-
 all-packages -i.. -i../libraries/base/. -i../libraries/base/dist-
 install/build -I../libraries/base/dist-install/build -i../libraries/base
 /dist-install/build/./autogen -I../libraries/base/dist-
 install/build/./autogen -Ilibraries/base/include   -optP-
 DOPTIMISE_INTEGER_GCD_LCM -optP-include -optP../libraries/base/dist-
 install/build/./autogen/cabal_macros.h -package-id rts -package-id ghc-
 prim-0.5.0.0 -package-id integer-gmp-1.0.0.1 -this-unit-id base
 -XHaskell2010 -O2  -no-user-package-db -rtsopts -Wno-trustworthy-safe
 -Wno-deprecated-flags     -Wnoncanonical-monad-instances  -odir
 libraries/base/dist-install/build -hidir libraries/base/dist-install/build
 -stubdir libraries/base/dist-install/build  -split-sections -dynamic-too
 -c Bug.hs -fforce-recomp

 ghc-stage1: panic! (the 'impossible' happened)
   (GHC version 8.3.20170506 for x86_64-unknown-linux):
         ASSERT failed!
   optCoercion changed types!
   in_co:
     (TypeRep
        (UnsafeCo nominal Any (Any -> Any))
        (UnsafeCo nominal (Any Any) Any))_R
   in_ty1: TypeRep (Any Any)
   in_ty2: TypeRep Any
   out_co: (TypeRep (UnsafeCo nominal Any (Any -> Any)) <Any>_N)_R
   out_ty1: TypeRep Any
   out_ty2: TypeRep Any
   subst:
     [TCvSubst
        In scope: InScope {wild_00 wild_Xu y_a1t ys_a1u a_ayL $krep_aAd
                           $krep_aAe $krep_aAf $krep_aAg $krep_aAh
 $krep_aAi $krep_aAj
                           $krep_aAk $krep_aAl $krep_aAm undefined
 $tcTypeRep $tcSomeTypeRep
                           $tc'TrTyCon $tc'TrApp $trModule $tc'SomeTypeRep
 bug $trModule_sB4
                           $trModule_sB5 $trModule_sB6 $trModule_sB7
 $tcTypeRep_sB8
                           $tcTypeRep_sB9 $krep_sBa $krep_sBb
 $tc'TrTyCon_sBc $tc'TrTyCon_sBd
                           $krep_sBe $krep_sBf $tc'TrApp_sBg $tc'TrApp_sBh
 $tcSomeTypeRep_sBi
                           $tcSomeTypeRep_sBj $tc'SomeTypeRep_sBk
 $tc'SomeTypeRep_sBl
                           poly_go_sBz lvl_sBA $spoly_go_sCu sc_sCv sc_sCw
 $spoly_go_sCx}
        Type env: []
        Co env: []]
   Call stack:
       CallStack (from HasCallStack):
         prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:1134:58 in ghc:Outputable
         callStackDoc, called at compiler/utils/Outputable.hs:1189:22 in
 ghc:Outputable
         assertPprPanic, called at compiler/types/OptCoercion.hs:96:188 in
 ghc:OptCoercion
   Call stack:
       CallStack (from HasCallStack):
         prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:1134:58 in ghc:Outputable
         callStackDoc, called at compiler/utils/Outputable.hs:1138:37 in
 ghc:Outputable
         pprPanic, called at compiler/utils/Outputable.hs:1187:5 in
 ghc:Outputable
         assertPprPanic, called at compiler/types/OptCoercion.hs:96:188 in
 ghc:OptCoercion
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13658#comment:3>
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