[GHC] #12709: GHC panic

[GHC]

#12709: GHC panic
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  LevityPolymorphism
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Richard Eisenberg <rae@…>):

 In [changeset:"dca44adb9e14992e0aed49cdfd4b2baa2182073b/ghc"
 dca44adb/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="dca44adb9e14992e0aed49cdfd4b2baa2182073b"
 Fix #12709 by not building bad applications

 In an effort to report multiple levity polymorphism errors all at
 once, the desugarer does not fail when encountering bad levity
 polymorphism. But we must be careful not to build the bad applications,
 lest they try to satisfy the let/app invariant and call
 isUnliftedType on a levity polymorphic type. This protects calls
 to mkCoreAppDs appropriately.

 test case: typecheck/should_fail/T12709
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12709#comment:5>
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