[GHC] #7447: Stale .hi files affect compilation.

[GHC]

#7447: Stale .hi files affect compilation.
-------------------------+--------------------------------------------------
Reporter:  int-e         |          Owner:                
    Type:  bug           |         Status:  new           
Priority:  normal        |      Component:  Compiler      
 Version:  7.6.1         |       Keywords:                
      Os:  Linux         |   Architecture:  x86_64 (amd64)
 Failure:  None/Unknown  |      Blockedby:                
Blocking:                |        Related:                
-------------------------+--------------------------------------------------
 I saw the following odd behaviour while playing with the example from
 #7446. Strangely, whether the warning (unusuable UNPACK pragma) is printed
 or not depends on the presence and contents of a .hi file despite of
 {{{--fforce-recomp}}} and even if the source file was modified.

 {{{
 > rm -f Peaker.*
 > ghc --version
 The Glorious Glasgow Haskell Compilation System, version 7.6.1

 > echo 'module Peaker(V(..)) where{ data V = V {-# UNPACK #-} !L; data L =
 L V }' > Peaker.hs
 > ghc -fforce-recomp -O1 Peaker.hs
 [1 of 1] Compiling Peaker           ( Peaker.hs, Peaker.o )

 Peaker.hs:1:38: Warning:
     Ignoring unusable UNPACK pragma on the first argument of `V'
     In the definition of data constructor `V'
     In the data declaration for `V'
 > ghc -fforce-recomp -O1 Peaker.hs
 [1 of 1] Compiling Peaker           ( Peaker.hs, Peaker.o )

 Peaker.hs:1:38: Warning:
     Ignoring unusable UNPACK pragma on the first argument of `V'
     In the definition of data constructor `V'
     In the data declaration for `V'
 > rm Peaker.hi
 > ghc -fforce-recomp -O1 Peaker.hs
 [1 of 1] Compiling Peaker           ( Peaker.hs, Peaker.o )

 Peaker.hs:1:38: Warning:
     Ignoring unusable UNPACK pragma on the first argument of `V'
     In the definition of data constructor `V'
     In the data declaration for `V'

 > echo 'module Peaker(L(..)) where{ data V = V {-# UNPACK #-} !L; data L =
 L V }' > Peaker.hs
 > ghc -fforce-recomp -O1 Peaker.hs
 [1 of 1] Compiling Peaker           ( Peaker.hs, Peaker.o )

 Peaker.hs:1:38: Warning:
     Ignoring unusable UNPACK pragma on the first argument of `V'
     In the definition of data constructor `V'
     In the data declaration for `V'
 > ghc -fforce-recomp -O1 Peaker.hs
 [1 of 1] Compiling Peaker           ( Peaker.hs, Peaker.o )
 > rm Peaker.hi
 > ghc -fforce-recomp -O1 Peaker.hs
 [1 of 1] Compiling Peaker           ( Peaker.hs, Peaker.o )

 Peaker.hs:1:38: Warning:
     Ignoring unusable UNPACK pragma on the first argument of `V'
     In the definition of data constructor `V'
     In the data declaration for `V'

 > echo 'module Peaker(V(..)) where{ data V = V {-# UNPACK #-} !L; data L =
 L V }' > Peaker.hs
 > ghc -fforce-recomp -O1 Peaker.hs
 [1 of 1] Compiling Peaker           ( Peaker.hs, Peaker.o )
 > ghc -fforce-recomp -O1 Peaker.hs
 [1 of 1] Compiling Peaker           ( Peaker.hs, Peaker.o )

 Peaker.hs:1:38: Warning:
     Ignoring unusable UNPACK pragma on the first argument of `V'
     In the definition of data constructor `V'
     In the data declaration for `V'
 > rm Peaker.hi
 > ghc -fforce-recomp -O1 Peaker.hs
 [1 of 1] Compiling Peaker           ( Peaker.hs, Peaker.o )

 Peaker.hs:1:38: Warning:
     Ignoring unusable UNPACK pragma on the first argument of `V'
     In the definition of data constructor `V'
     In the data declaration for `V'
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7447>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler