[GHC] #8929: Deriving Generics broken

[GHC]

#8929: Deriving Generics broken
-------------------------------------+----------------------------------
        Reporter:  guest             |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.6.3
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Old description:

> I load the following code into ghci:
>
> ==
> {-# LANGUAGE DeriveGeneric #-}
>
> import GHC.Generics
> import Data.Binary
>
> data Foo = Foo deriving (Show, Generic)
>
> instance Binary Foo
> ==
>
> Then I execute:
>
> (decode . encode $ Foo) :: Foo
>
> In 7.6.3 (stage 2 booted 7.6.3), I get an error.
>
> In 7.6.3 (stage 2 booted 7.6.2), the desired result "Foo" is shown.

New description:

 I load the following code into ghci:

 {{{#!hs
 {-# LANGUAGE DeriveGeneric #-}

 import GHC.Generics
 import Data.Binary

 data Foo = Foo deriving (Show, Generic)

 instance Binary Foo
 }}}

 Then I execute:

 {{{#!hs
 (decode . encode $ Foo) :: Foo
 }}}

 In 7.6.3 (stage 2 booted 7.6.3), I get an error.

 In 7.6.3 (stage 2 booted 7.6.2), the desired result "Foo" is shown.

--

Comment (by hvr):

 (fixed up Wiki markup)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8929#comment:4>
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