[GHC] #8029: batch-mode recompilation checking sometimes fails

[GHC]

#8029: batch-mode recompilation checking sometimes fails
-----------------------------+----------------------------------------------
Reporter:  jwlato            |          Owner:                           
    Type:  bug               |         Status:  new                      
Priority:  normal            |      Component:  Compiler                 
 Version:  7.6.3             |       Keywords:  recompilation, batch-mode
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple         
 Failure:  None/Unknown      |      Blockedby:                           
Blocking:                    |        Related:                           
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 The batch-mode recompilation checker seems to be broken.  Suppose you have
 a source tree with

 {{{
     Data/List.hs
     Data/Top.hs
 }}}

 and Data/List.hs defining 'foo' and Data/Top.hs importing Data.List (local
 file).  Compile Data/Top.hs, then rename Data.List so you have

 {{{
     Data/List.{hi,o}
     Data/OtherList.hs  -- exports 'foo'
     Data/Top.hs        -- imports Data.List and Data.OtherList
     Data/Top.{hi.o}
 }}}

 Attempting to run 'ghc -c Data/Top.hs' will now fail with "    Failed to
 load interface for `Data.OtherList'".  This error appears to be specific
 to built-in modules, if I use a library module (e.g. Data.Vector from the
 vector package) I instead get an error that multiple definitions of 'foo'
 are in scope.

 A test repo is available at https://github.com/JohnLato/tripping-octo-
 avenger

 Incidentally, everything works if I use 'ghc -c --make'.  I think a
 reasonable fix would be for --make to be on by default for batch-mode
 compilation as well.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/8029>
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