#15170: GHC HEAD panic (dischargeFmv)
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Reporter: RyanGlScott | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone: 8.6.1
Component: Compiler (Type | Version: 8.5
checker) |
Resolution: | Keywords: TypeInType
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: |
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Comment (by RyanGlScott):
Here's as small of an example as I can muster:
{{{#!hs
{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeInType #-}
{-# LANGUAGE TypeOperators #-}
module Bug where
import Data.Kind
import Data.Proxy
data TyFun :: Type -> Type -> Type
type a ~> b = TyFun a b -> Type
infixr 0 ~>
type family Apply (f :: k1 ~> k2) (x :: k1) :: k2
type f @@ x = Apply f x
infixl 9 @@
wat :: forall (a :: Type)
(b :: a ~> Type)
(c :: forall (x :: a). Proxy x ~> b @@ x ~> Type)
(f :: forall (x :: a) (y :: b @@ x). Proxy x ~> Proxy y ~> c
@@ ('Proxy :: Proxy x) @@ y)
(x :: a).
(forall (xx :: a) (yy :: b @@ xx). Proxy (f @@ ('Proxy :: Proxy xx)
@@ ('Proxy :: Proxy yy)))
-> ()
wat _ = ()
}}}
{{{
$ /opt/ghc/head/bin/ghc Bug.hs
[1 of 1] Compiling Bug ( Bug.hs, Bug.o )
ghc: panic! (the 'impossible' happened)
(GHC version 8.5.20180501 for x86_64-unknown-linux):
dischargeFmv
[D] _ {0}:: (Apply
(f_a1rx[sk:2] xx_a1rH[tau:3] yy_a1rI[tau:3] |> Sym
((TyFun