Core lint failure with TypeLits Symbol
The following module:
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE ScopedTypeVariables #-}
module Bug where
import GHC.TypeLits ( Symbol, KnownSymbol )
--------------------------------------------------------------------------------
data Meta = MetaCons Symbol
data M1 (c :: Meta) = M1
class Generic a where
type Rep a :: *
from :: a -> Rep a
--------------------------------------------------------------------------------
data A = A1
instance Generic A where
type Rep A = M1 ('MetaCons "test")
from A1 = M1
class GShow' f where
gshowsPrec' :: f -> ShowS
instance (KnownSymbol c) => GShow' (M1 ('MetaCons c))
instance GShow' A where gshowsPrec' = gshowsPrec' . from
fails -dcore-lint
in HEAD with:
*** Core Lint errors : in result of Desugar (after optimization) ***
<no location info>: Warning:
[RHS of $dKnownSymbol_azn :: GHC.TypeLits.KnownSymbol "test"]
From-type of Cast differs from type of enclosed expression
From-type: GHC.TypeLits.KnownSymbol "test"
Type of enclosed expr: [GHC.Types.Char]
Actual enclosed expr: GHC.CString.unpackCString# "test"#
Coercion used in cast: GHC.TypeLits.NTCo:KnownSymbol[0] <"test">_N
; GHC.TypeLits.NTCo:SSymbol[0] <"test">_P
Trac metadata
Trac field | Value |
---|---|
Version | 7.9 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |