[GHC] #11230: No run-time exception for deferred type errors when error is in a phantom role position

[GHC]

#11230: No run-time exception for deferred type errors when error is in a phantom
role position
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        Reporter:  darchon           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:  deferred,
                                     |  roles
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1641
       Wiki Page:                    |
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Comment (by Richard Eisenberg <eir@…>):

 In [changeset:"1722fa106e10e63160bb2322e2ccb830fd5b9ab3/ghc"
 1722fa10/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="1722fa106e10e63160bb2322e2ccb830fd5b9ab3"
 Fix #11230.

 Previously, we were optimizing away all case expressions over
 coercions with dead binders. But sometimes we want to force
 the coercion expression. Like when it contains an error.

 Test case: typecheck/should_run/T11230
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11230#comment:6>
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