[GHC] #11596: ghci gets confused if a file is deleted

[GHC]

#11596: ghci gets confused if a file is deleted
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           Reporter:  NeilMitchell   |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  GHCi           |           Version:  8.0.1-rc2
           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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 With GHC 8.0 RC2 if a currently loaded .hs file is deleted then
 {{{:reload}}} works, but actual execution of anything is broken. In
 previous versions this situation resulted in an error at {{{:reload}}}
 time. Below is a session that demonstrate the bug:

 {{{
 $ ghci A.hs
 GHCi, version 8.0.0.20160205: http://www.haskell.org/ghc/  :? for help
 [1 of 2] Compiling B                ( B.hs, interpreted )
 [2 of 2] Compiling A                ( A.hs, interpreted )
 Ok, modules loaded: A, B.
 *A> :!cat A.hs
 module A where
 import B
 a = b + 1
 *A> :!cat B.hs
 module B where
 b = 41
 *A> :!mv B.hs B.txt
 *A> :r
 Ok, modules loaded: A.
 *A> :show modules
 A                ( A.hs, interpreted )
 *A> a
 <interactive>: fatal:
     cannot find object file for module `B'
     while linking an interpreted expression
 *A> :r
 Ok, modules loaded: A.
 }}}

 Specifically, I load A.hs, which depends on B.hs. I move B.hs away (or
 delete it). I reload and it says everything is fine. I try to run and it
 fails. Putting the B.hs file back solves it. This sequence worked fine in
 all previous versions of GHC, and is caught by the
 [https://github.com/ndmitchell/ghcid ghcid] test suite.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11596>
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