GHC HEAD-only Core Lint error with unboxed equality (Non-CoVar has coercion type)
module Foo where
import Language.Haskell.TH.Lib
import Language.Haskell.TH.Syntax
ueqT :: Q Type
ueqT = conT $ mkNameG_tc "ghc-prim" "GHC.Prim" "~#"{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE TemplateHaskell #-}
module Bug where
import Data.Kind
import Foo (ueqT)
data JankyEquality :: Type -> Type -> Type where
Jank :: $ueqT a b -> JankyEquality a b
unJank :: JankyEquality a b -> $ueqT a b
unJank (Jank x) = x$ ~/Software/ghc5/inplace/bin/ghc-stage2 --interactive Bug.hs -dcore-lint
GHCi, version 8.7.20190115: https://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
[1 of 2] Compiling Foo ( Foo.hs, interpreted )
[2 of 2] Compiling Bug ( Bug.hs, interpreted )
*** Core Lint errors : in result of Desugar (before optimization) ***
<no location info>: warning:
In a case alternative: (Jank x_a4vR :: a_a4wC ~# b_a4wD)
Non-CoVar has coercion type x_a4vR :: a_a4wC ~# b_a4wD
*** Offending Program ***
<elided>
unJank :: forall a b. JankyEquality a b -> a ~# b
[LclIdX]
unJank
= \ (@ a_a4wC)
(@ b_a4wD)
(ds_d4wN :: JankyEquality a_a4wC b_a4wD) ->
case ds_d4wN of wild_00 { Jank x_a4vR -> break<0>() x_a4vR }Note that this passes -dcore-lint on GHC 8.0.2 through 8.6.3.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.6.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |