[GHC] #8028: Panic on degenerate closed type family

[GHC]

#8028: Panic on degenerate closed type family
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        Reporter:  monoidal                      |         Owner:  goldfire
            Type:  bug                           |        Status:  closed
        Priority:  normal                        |     Milestone:
       Component:  Compiler (Type checker)       |       Version:  7.7
      Resolution:  fixed                         |      Keywords:
Operating System:  Unknown/Multiple              |  Architecture:
 Type of failure:  Incorrect warning at          |  Unknown/Multiple
  compile-time                                   |     Test Case:
      Blocked By:                                |      Blocking:
 Related Tickets:                                |
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Comment (by Adam Gundry <adam@…>):

 In [changeset:"4efa421327cf127ebefde59b2eece693e37dc3c6/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="4efa421327cf127ebefde59b2eece693e37dc3c6"
 Permit empty closed type families

 Fixes #9840 and #10306, and includes an alternative resolution to #8028.
 This permits empty closed type families, and documents them in the user
 guide. It updates the Haddock submodule to support the API change.

 Test Plan: Added `indexed-types/should_compile/T9840` and updated
 `indexed-types/should_fail/ClosedFam4` and `th/T8028`.

 Reviewers: austin, simonpj, goldfire

 Reviewed By: goldfire

 Subscribers: bgamari, jstolarek, thomie, goldfire

 Differential Revision: https://phabricator.haskell.org/D841

 GHC Trac Issues: #9840, #10306
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8028#comment:4>
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