[GHC] #15481: TH fails to recover from reifyFixity with -fexternal-interpreter

[GHC]

#15481: TH fails to recover from reifyFixity with -fexternal-interpreter
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Template Haskell  |              Version:  8.4.3
      Resolution:                    |             Keywords:  RemoteGHCi
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 RyanGlScott):

 Interestingly, if you invoke `fail` anywhere in the second argument to
 `recover`:

 {{{#!hs
 main :: IO ()
 main = putStrLn $(recover (stringE "reifyFixity failed")
                           (do foo <- newName "foo"
                               _ <- reifyFixity foo
                               fail "wat"
                               stringE "reifyFixity successful"))
 }}}

 Then `-fexternal-interpreter` will successfully recover again.

 Also, there appears to be something specific to `reifyFixity` that
 triggers this bug. If I replace `reifyFixity` with `reify` or
 `reifyConStrictness`, then `-fexternal-interpreter` is able to
 successfully recover from those.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15481#comment:2>
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