[GHC] #10817: Looping default associated type family without UndecidableInstances

[GHC]

#10817: Looping default associated type family without UndecidableInstances
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        Reporter:  goldfire          |                   Owner:
            Type:  bug               |                  Status:  patch
        Priority:  normal            |               Milestone:
       Component:  Compiler (Type    |                 Version:  7.10.2
  checker)                           |
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D1262
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Comment (by Richard Eisenberg <eir@…>):

 In [changeset:"e27b267f3675180c03a75282dd952b8a59339a1f/ghc" e27b267/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="e27b267f3675180c03a75282dd952b8a59339a1f"
 Perform a validity check on assoc type defaults.

 This fixes #10817 and #10899. A knock-on effect is that we must
 now remember locations of associated type defaults for error
 messages during validity checking. This isn't too bad, but it
 increases the size of the diff somewhat.

 Test cases: indexed-types/should_fail/T108{17,99}
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10817#comment:4>
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