#4912: No warnings for orphan instances declared via TypeSynonymInstances
---------------------------------+------------------------------------------
Reporter: batterseapower | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.0.1 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Incorrect warning at
compile-time
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File Classes.hs:
{{{
module Classes where
data TheirData = TheirData
class Foo a where
foo :: a -> a
class Bar a where
bar :: a -> String
}}}
File Orphans.hs:
{{{
{-# LANGUAGE TypeSynonymInstances #-}
module Orphans where
import Classes
type OurData = TheirData
instance Foo TheirData where
foo = id
instance Bar OurData where
bar _ = "Ours"
}}}
Compile:
{{{
$ ghc --make -fforce-recomp -fwarn-orphans Orphans.hs
[1 of 2] Compiling Classes ( Classes.hs, Classes.o )
[2 of 2] Compiling Orphans ( Orphans.hs, Orphans.o )
Orphans.hs:9:10: Warning: orphan instance: instance Foo TheirData
}}}
This is not my expected result. We should get orphan instance warnings for
Bar OurData as well, since OurData is just a thinly-disguised version of
TheirData.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4912>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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