Don't try and resolve dependencies for packages that are not buildable

[batterseapower]

I had a component like this:

Executable edit-distance-benchmark
        Main-Is:                Text/EditDistance/Benchmark.hs
        
        if flag(splitBase)
                Build-Depends:  base >= 3 && < 5, array >= 0.1, random >= 1.0, old-time >= 1.0, process >= 1.0,
                                parallel >= 1.0, unix >= 2.3
        else
                Build-Depends:  base < 3,
                                parallel >= 1.0, unix >= 2.3
        
        if !flag(benchmark)
                Buildable:      False
            
        Ghc-Options:            -O2 -fvia-C -Wall

However, I've only just found out that this meant that you couldn't install any parts of my package on Windows, because Cabal tried to resolve the "unix" dependency even if "benchmark" was False (the default)!

I've solved this like so:

Executable edit-distance-benchmark
        Main-Is:                Text/EditDistance/Benchmark.hs
        
        if !flag(benchmark)
                Buildable:      False
        else
                if flag(splitBase)
                        Build-Depends:  base >= 3 && < 5, array >= 0.1, random >= 1.0, old-time >= 1.0, process >= 1.0,
                                        parallel >= 1.0, unix >= 2.3
                else
                        Build-Depends:  base < 3,
                                        parallel >= 1.0, unix >= 2.3
            
        Ghc-Options:            -O2 -fvia-C -Wall

But really Cabal should not need to resolve dependencies for things that are not buildable.

[duncan]

The semantics for "buildable: False" is actually rather tricky. We don't have a precise description of what it should mean. See this discussion:  http://haskell.org/pipermail/glasgow-haskell-users/2009-December/018155.html

[elga]

*  simyo