[cabal] Extract simple static information from PackageDescription

[Daniel Trstenjak]

Hi Jakob,

you might like the cabal-lenses[1] library.

Getting 'hs-source-dirs' from all sections of the cabal file (library,
executable, ...) and evaluating the conditionals in the cabal file
(considering the default value of flags and the current platform), you
should be able to write:

   import Control.Lens   -- from the lens library
   import CabalLenses    -- from the cabal-lenses library

   hsSourceDirs :: GenericPackageDescription -> [String]
   hsSourceDirs pkgDesc = pkgDesc ^.. allBuildInfo . traversed . hsSourceDirsL

You can also specify[2] which section you like to read or how flags
for the conditionals should be set.


If you only need a command line programming for the reading of 'hs-source-dirs',
then there's cabal-cargs[3]. The above example:

   cabal-cargs --only=hs_source_dirs --format=pure


Greetings,
Daniel


[1] https://hackage.haskell.org/package/cabal-lenses-0.4.7
[2] https://hackage.haskell.org/package/cabal-lenses-0.4.5/docs/CabalLenses-Traversals-BuildInfo.html
[3] https://hackage.haskell.org/package/cabal-cargs