[GHC] #13068: GHC should not allow modules to define instances of abstract type classes

[GHC]

#13068: GHC should not allow modules to define instances of abstract type classes
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        Reporter:  ezyang            |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  low               |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:  backpack
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3254
       Wiki Page:                    |
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Comment (by Edward Z. Yang <ezyang@…>):

 In [changeset:"bba004f2a0642d3bb8c8876543aaa1a48a2f9a43/ghc"
 bba004f2/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="bba004f2a0642d3bb8c8876543aaa1a48a2f9a43"
 Prevent users from defining instances for abstract classes.

 Summary:
 Fixes #13068.

 Signed-off-by: Edward Z. Yang <ezyang at cs.stanford.edu>

 Test Plan: validate

 Reviewers: simonpj, austin, bgamari

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D3254
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13068#comment:3>
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