[GHC] #14396: Hs-boot woes during family instance consistency checks

[GHC]

#14396: Hs-boot woes during family instance consistency checks
-------------------------------------+-------------------------------------
        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      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:D4154
       Wiki Page:                    |
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Comment (by ezyang):

 I attempted to trigger the error case simonpj described, with the new
 patchset, by writing this T.hs instead:

 {{{
 -- T.hs
 module T where
   import T1
   import T2
   data SyntaxExpr = S
 f :: XListPat Int -> ()
 f S = ()
 }}}

 But I didn't succeed. The idea is that type family consistency checking
 might have caused the family instance to force the thunk for SyntaxExpr
 early, so that the instance reduction will point to the wrong thing, but
 this does not seem to have happened.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14396#comment:10>
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