[GHC] #16392: In ghci, revertCAFs should be executed in the external interpreter when necessary

[GHC]

#16392: In ghci, revertCAFs should be executed in the external interpreter when
necessary
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           Reporter:  lolotp         |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  GHCi           |           Version:  8.6.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I believe this bug was discovered and reported earlier here,
 https://mail.haskell.org/pipermail/ghc-devs/2018-June/015842.html. I
 stumbled upon this while tracking down a problem with ghci.

 To describe the problem, we call revertCAFs whenever we load modules in
 ghci so that they can be re-evaluated. This however, doesn't work as
 intended when use with `-fexternal-interpreter` because the CAFs of loaded
 modules actually live in the external interpreter process instead while
 `revertCAFs` only work for CAFs in the ghci process.

 To fix this, we should call revertCAFs in the external interpreter when
 it's used.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16392>
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