#15318: Core Lint error involving newtype family instances with wrappers
-------------------------------------+-------------------------------------
Reporter: RyanGlScott | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone: 8.6.1
Component: Compiler | Version: 8.4.3
(Type checker) |
Keywords: TypeFamilies | 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:
-------------------------------------+-------------------------------------
The following program gives a Core Lint error on GHC 8.4 and later:
{{{#!hs
{-# LANGUAGE GADTs #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeFamilies #-}
module Bug where
data family Sn a
newtype instance Sn (Either a b) where
SnC :: forall b a. Char -> Sn (Either a b)
}}}
{{{
$ /opt/ghc/8.4.3/bin/ghc -dcore-lint Bug.hs
[1 of 1] Compiling Bug ( Bug.hs, Bug.o )
*** Core Lint errors : in result of Tidy Core ***
<no location info>: warning:
[in body of lambda with binder dt_aZm :: Char]
From-type of Cast differs from type of enclosed expression
From-type: R:SnEither a_auS b_auR
Type of enclosed expr: Sn (Either a_auS b_auR)
Actual enclosed expr: dt_aZm
`cast` (Sym (N:R:SnEither[0]
_N _N) ; Sym
(D:R:SnEither0[0]
_N _N)
:: (Char :: *) ~R# (Sn (Either a_auS
b_auR) :: *))
Coercion used in cast: Sym (D:R:SnEither0[0] _N _N)
*** Offending Program ***
$WSnC [InlPrag=INLINE[2]] :: forall b a. Char -> Sn (Either a b)
[GblId[DataConWrapper],
Arity=1,
Caf=NoCafRefs,
Str=,
Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
WorkFree=True, Expandable=True,
Guidance=ALWAYS_IF(arity=1,unsat_ok=True,boring_ok=True)
Tmpl= \ (@ b_auR) (@ a_auS) (dt_aZm [Occ=Once] :: Char) ->
(dt_aZm
`cast` (Sym (N:R:SnEither[0]
_N _N) ; Sym
(D:R:SnEither0[0] _N _N)
:: (Char :: *) ~R# (Sn (Either a_auS b_auR) ::
*)))
`cast` (Sym (D:R:SnEither0[0] _N _N)
:: (R:SnEither a_auS b_auR :: *)
~R# (Sn (Either a_auS b_auR) :: *))}]
$WSnC
= \ (@ b_auR) (@ a_auS) (dt_aZm [Occ=Once] :: Char) ->
(dt_aZm
`cast` (Sym (N:R:SnEither[0]
_N _N) ; Sym (D:R:SnEither0[0]
_N _N)
:: (Char :: *) ~R# (Sn (Either a_auS b_auR) :: *)))
`cast` (Sym (D:R:SnEither0[0] _N _N)
:: (R:SnEither a_auS b_auR :: *)
~R# (Sn (Either a_auS b_auR) :: *))
$trModule1_r10g :: Addr#
[GblId, Caf=NoCafRefs]
$trModule1_r10g = "main"#
$trModule2_r10D :: TrName
[GblId, Caf=NoCafRefs]
$trModule2_r10D = TrNameS $trModule1_r10g
$trModule3_r10E :: Addr#
[GblId, Caf=NoCafRefs]
$trModule3_r10E = "Bug"#
$trModule4_r10F :: TrName
[GblId, Caf=NoCafRefs]
$trModule4_r10F = TrNameS $trModule3_r10E
$trModule :: Module
[GblId, Caf=NoCafRefs]
$trModule = Module $trModule2_r10D $trModule4_r10F
$krep_r10G :: KindRep
[GblId]
$krep_r10G = KindRepTyConApp $tcChar ([] @ KindRep)
$krep1_r10H :: KindRep
[GblId, Caf=NoCafRefs]
$krep1_r10H = KindRepVar 1#
$krep2_r10I :: KindRep
[GblId, Caf=NoCafRefs]
$krep2_r10I = KindRepVar 0#
$krep3_r10J :: [KindRep]
[GblId, Caf=NoCafRefs]
$krep3_r10J = : @ KindRep $krep2_r10I ([] @ KindRep)
$krep4_r10K :: [KindRep]
[GblId, Caf=NoCafRefs]
$krep4_r10K = : @ KindRep $krep1_r10H $krep3_r10J
$krep5_r10L :: KindRep
[GblId]
$krep5_r10L = KindRepTyConApp $tcEither $krep4_r10K
$tcSn1_r10M :: Addr#
[GblId, Caf=NoCafRefs]
$tcSn1_r10M = "Sn"#
$tcSn2_r10N :: TrName
[GblId, Caf=NoCafRefs]
$tcSn2_r10N = TrNameS $tcSn1_r10M
$tcSn :: TyCon
[GblId]
$tcSn
= TyCon
461968091845555535##
16320521938866097056##
$trModule
$tcSn2_r10N
0#
krep$*Arr*
$krep6_r10O :: [KindRep]
[GblId]
$krep6_r10O = : @ KindRep $krep5_r10L ([] @ KindRep)
$krep7_r10P :: KindRep
[GblId]
$krep7_r10P = KindRepTyConApp $tcSn $krep6_r10O
$krep8_r10Q :: KindRep
[GblId]
$krep8_r10Q = KindRepFun $krep_r10G $krep7_r10P
$tc'SnC1_r10R :: Addr#
[GblId, Caf=NoCafRefs]
$tc'SnC1_r10R = "'SnC"#
$tc'SnC2_r10S :: TrName
[GblId, Caf=NoCafRefs]
$tc'SnC2_r10S = TrNameS $tc'SnC1_r10R
$tc'SnC :: TyCon
[GblId]
$tc'SnC
= TyCon
3818830880305712792##
17484539998814842835##
$trModule
$tc'SnC2_r10S
2#
$krep8_r10Q
*** End of Offense ***
<no location info>: error:
Compilation had errors
}}}
If we look at the Core for `$WSnC`, we see the culprit:
{{{
$WSnC
= \ (@ b_auR) (@ a_auS) (dt_aZm [Occ=Once] :: Char) ->
(dt_aZm
`cast` (Sym (N:R:SnEither[0]
_N _N) ; Sym (D:R:SnEither0[0]
_N _N)
:: (Char :: *) ~R# (Sn (Either a_auS b_auR) :: *)))
`cast` (Sym (D:R:SnEither0[0] _N _N)
:: (R:SnEither a_auS b_auR :: *)
~R# (Sn (Either a_auS b_auR) :: *))
}}}
The inner cast goes from `Char` to `Sn (Either a b)`, but then the outer
cast goes from `R:SnEither a b` to `Sn (Either a b)`, which is not
transitive.
--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15318
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler
