[GHC] #13347: Abstract classes in hs-boot should not be treated as injective

[GHC]

#13347: Abstract classes in hs-boot should not be treated as injective
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        Reporter:  ezyang            |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  low               |            Milestone:
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:  hs-boot
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3236
       Wiki Page:                    |
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Comment (by Edward Z. Yang <ezyang@…>):

 In [changeset:"fb5cd9d6d6185afe6d4ef2f3df3f895b6d0abf4c/ghc" fb5cd9d/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="fb5cd9d6d6185afe6d4ef2f3df3f895b6d0abf4c"
 Properly represent abstract classes in Class and IfaceDecl

 Summary:
 Previously, abstract classes looked very much like normal
 classes, except that they happened to have no methods,
 superclasses or ATs, and they came from boot files.  This
 patch gives abstract classes a proper representation in
 Class and IfaceDecl, by moving the things which are never
 defined for abstract classes into ClassBody/IfaceClassBody.

 Because Class is abstract, this change had ~no disruption
 to any of the code in GHC; if you ask about the methods of
 an abstract class, we'll just give you an empty list.

 This also fixes a bug where abstract type classes were incorrectly
 treated as representationally injective (they're not!)

 Fixes #13347, and a TODO in the code.

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

 Test Plan: validate

 Reviewers: simonpj, bgamari, austin

 Subscribers: goldfire, thomie

 Differential Revision: https://phabricator.haskell.org/D3236
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13347#comment:3>
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