Stale .hi files affect compilation.

I saw the following odd behaviour while playing with the example from #7446 (closed). 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'

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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