[GHC] #5147: GHCi ignores missing instance

[GHC]

#5147: GHCi ignores missing instance
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    Reporter:  boris                  |        Owner:                             
        Type:  bug                    |       Status:  new                        
    Priority:  normal                 |    Milestone:  7.4.1                      
   Component:  GHCi                   |      Version:  7.0.2                      
    Keywords:  linker, data families  |     Testcase:                             
   Blockedby:                         |   Difficulty:                             
          Os:  Unknown/Multiple       |     Blocking:                             
Architecture:  Unknown/Multiple       |      Failure:  GHC accepts invalid program
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Comment(by simonpj@…):

 commit 3bf0520aea5acbecb83dcc0fc722c79ce9f5723c
 {{{
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Wed Aug 3 07:46:50 2011 +0100

     Include the instances of associated types in the "extras" of a class

     This fixes Trac #5147, which was going wrong because
     the class ABI fingerprint wasn't changing when we added
     or removed a Show instance to the associated type.

  compiler/iface/IfaceSyn.lhs |   10 +++++++++-
  compiler/iface/MkIface.lhs  |   24 ++++++++++++++++++++----
  2 files changed, 29 insertions(+), 5 deletions(-)
 }}}

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5147#comment:3>
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