[GHC] #13616: Old file used when later calls to GHC omit -dynamic-too

26 Apr 2017

      #13616: Old file used when later calls to GHC omit -dynamic-too
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           Reporter:  nomeata        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           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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 This may possibly only hurt few people who develop Plugins, but it is
 still quite annoying: If `ghc`, in `--make` mode, recompiles a plugin that
 it is going to use, but without `-dynamic-too`, it will create new `.dyn`
 and `.o` files, but it will happily use the old `.dyn_hs` or `.dyn_o`
 files that are still lying around.

 I guess the desired behavior is: If it determines that it needs the
 dynamically compiled version of some module, and it is recompiling the
 module, then it should complain instead of later either ungracefully
 falling over the missing `.dyn_o` file or – worse – using an old one.

 This script reproduces the issue:
 {{{
 #!/bin/bash

 rm -f *.o *.hi *.dyn_o *.dyn_hi

 cat > Plugin.hs <<__END__
 module Plugin where
 import GhcPlugins
 plugin :: Plugin
 plugin = defaultPlugin { installCoreToDos = install }

 install :: [CommandLineOption] -> [CoreToDo] -> CoreM [CoreToDo]
 install _ _ = error "First version"
 __END__

 cat > Code.hs <<__END__
 {-# OPTIONS_GHC -O -fplugin Plugin #-}
 module Code where
 __END__

 echo "No dynamic file found (fine, but the error message could be more
 helpful)"

 ghc -package ghc Code.hs -fforce-recomp

 echo "Compiling with -dynamic-too"

 ghc -dynamic-too -package ghc Code.hs -fforce-recomp

 cat > Plugin.hs <<__END__
 module Plugin where
 import GhcPlugins
 plugin :: Plugin
 plugin = defaultPlugin { installCoreToDos = install }

 install :: [CommandLineOption] -> [CoreToDo] -> CoreM [CoreToDo]
 install _ _ = error "Second version"
 __END__

 echo "Recompiling without -dynamic-too, it still uses the old file"

 ghc -package ghc Code.hs -fforce-recomp

 echo "Recompiling with -dynamic-too, now it works"

 ghc -dynamic-too -package ghc Code.hs -fforce-recomp
 }}}
 And here is the slightly redacted output:
 {{{
 $ ./repro.sh
 No dynamic file found (fine, but the error message could be more helpful)
 [1 of 2] Compiling Plugin           ( Plugin.hs, Plugin.o )
 [2 of 2] Compiling Code             ( Code.hs, Code.o )
 <no location info>: fatal:
     cannot find object file ‘./Plugin.dyn_o’
     while linking an interpreted expression

 Compiling with -dynamic-too
 [1 of 2] Compiling Plugin           ( Plugin.hs, Plugin.o )
 [2 of 2] Compiling Code             ( Code.hs, Code.o )
 ghc: panic! (the 'impossible' happened)
         First version

 Recompiling without -dynamic-too, it still uses the old file
 [1 of 2] Compiling Plugin           ( Plugin.hs, Plugin.o )
 [2 of 2] Compiling Code             ( Code.hs, Code.o )
 ghc: panic! (the 'impossible' happened)
         First version

 Recompiling with -dynamic-too, now it works
 [1 of 2] Compiling Plugin           ( Plugin.hs, Plugin.o )
 [2 of 2] Compiling Code             ( Code.hs, Code.o )
 ghc: panic! (the 'impossible' happened)
         Second version
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13616
GHC http://www.haskell.org/ghc/
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