On 1 maj 2008, at 00.30, Duncan Coutts wrote:
If we look in xmonad.cabal we see:
library exposed-modules: XMonad XMonad.Main [...snip...] if flag(testing) buildable: False
So when the testing flag is True, the library will not be buildable. The hasLibs function actually only tells you about buildable libraries (the same goes for hasExes).
If you use flattenPackageDescription on this description you will get a PackageDescription whith buildable: False because flattening ignores all conditions and includes *both* sides of conditionals.
The key part here is that 'flattenPackageDescription' (more precisely 'unionBuildInfo' uses '&&' to join multiple occurences of buildable. If at any time a branch claims the package is not buildable, we, of course, want this property to be propagated. Using a '||' only for within flattenPackageDescription doesn't seem like a good idea to me.
So what you want is finalizePackageDescription to get a PackageDescription that reflects how the package can actually be configured given the environment in which you expect to use it.
I discussed this point with Brian O'Sullivan on irc the other day.
One API improvement we should do is to make hasLibs and similar functions take a parameter to say if you want to include or exclude buildable components since the choice is important and we've had a couple bugs in cabal because of this issue (for example bugs like not including non-buildable components in the source tarball).
Duncan
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