GHC panic from pattern synonyms + deferred type errors

{-# Language DataKinds, TypeOperators, PolyKinds, PatternSynonyms, GADTs #-}

{-# Options_GHC -dcore-lint -fdefer-type-errors #-}

import Data.Kind

data Ctx :: Type -> Type where
 E     :: Ctx(Type)
 (:&:) :: a -> Ctx(as) -> Ctx(a -> as)

data ApplyT (k::Type) :: k ->  Ctx(k) -> Type where
 AO :: a -> ApplyT(Type) a E
 AS :: ApplyT(ks)      (f a) ctx
    -> ApplyT(k -> ks) f     (a:&:ctx)

pattern ASSO = AS (AS (AO False))

$ ghci -ignore-dot-ghci 463.hs
hs/463.hs:16:27: warning: [-Wdeferred-type-errors]
    • Couldn't match type ‘a a1 a2’ with ‘Bool’
      Expected type: a3
        Actual type: Bool
    • In the pattern: False
      In the pattern: AO False
      In the pattern: AS (AO False)
   |
16 | pattern ASSO = AS (AS (AO False))
   |                           ^^^^^
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.7.20180828 for x86_64-unknown-linux):
	urk! lookup local fingerprint
  $mASSO
  [iESflb :-> ($trModule, 1ca40dc83a9c879effdb760462cc9a2d),
   iESgKD :-> ($tc'E, 79f67a27a14dc1bb6eecb39e4b061e2c),
   iESgKF :-> ($tc':&:, 24793c0c1652ffcf92e04f47d38fa075),
   iESgKH :-> ($tcCtx, a3f9358cbfe161bf59e75500d70ce0ae),
   iESgKI :-> ($tc'AO, 72111d1891cb082e989c20a2191a8b4b),
   iESgKK :-> ($tc'AS, ff019c04c400d5fbdd46ff8a816d4913),
   iESgKM :-> ($tcApplyT, cbfe28374b4115925c7213e6330ab115)]
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in ghc:Outputable
        pprPanic, called at compiler/iface/MkIface.hs:524:37 in ghc:MkIface

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

> 

Trac metadata

Trac field	Value
Version	8.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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