Merge commit '7b0b9f603bb1215e2b7af23c2404d637b95a4988' as 'hadrian'

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diff --git a/hadrian/src/Hadrian/Haskell/Cabal/Parse.hs b/hadrian/src/Hadrian/Haskell/Cabal/Parse.hs
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+-----------------------------------------------------------------------------
+-- |
+-- Module     : Hadrian.Haskell.Cabal.Parse
+-- Copyright  : (c) Andrey Mokhov 2014-2017
+-- License    : MIT (see the file LICENSE)
+-- Maintainer : andrey.mokhov@gmail.com
+-- Stability  : experimental
+--
+-- Extracting Haskell package metadata stored in Cabal files.
+-----------------------------------------------------------------------------
+module Hadrian.Haskell.Cabal.Parse (Cabal (..), parseCabal) where
+
+import Data.List.Extra
+import Development.Shake
+import Development.Shake.Classes
+import qualified Distribution.Package                  as C
+import qualified Distribution.PackageDescription       as C
+import qualified Distribution.PackageDescription.Parse as C
+import qualified Distribution.Text                     as C
+import qualified Distribution.Types.CondTree           as C
+import qualified Distribution.Verbosity                as C
+
+import Hadrian.Package
+
+-- TODO: Use fine-grain tracking instead of tracking the whole Cabal file.
+-- | Haskell package metadata extracted from a Cabal file.
+data Cabal = Cabal
+    { dependencies :: [PackageName]
+    , name         :: PackageName
+    , synopsis     :: String
+    , version      :: String
+    } deriving (Eq, Read, Show, Typeable)
+
+instance Binary Cabal where
+    put = put . show
+    get = fmap read get
+
+instance Hashable Cabal where
+    hashWithSalt salt = hashWithSalt salt . show
+
+instance NFData Cabal where
+    rnf (Cabal a b c d) = a `seq` b `seq` c `seq` d `seq` ()
+
+-- | Parse a Cabal file.
+parseCabal :: FilePath -> IO Cabal
+parseCabal file = do
+    gpd <- liftIO $ C.readGenericPackageDescription C.silent file
+    let pd      = C.packageDescription gpd
+        pkgId   = C.package pd
+        name    = C.unPackageName (C.pkgName pkgId)
+        version = C.display (C.pkgVersion pkgId)
+        libDeps = collectDeps (C.condLibrary gpd)
+        exeDeps = map (collectDeps . Just . snd) (C.condExecutables gpd)
+        allDeps = concat (libDeps : exeDeps)
+        sorted  = sort [ C.unPackageName p | C.Dependency p _ <- allDeps ]
+        deps    = nubOrd sorted \\ [name]
+    return $ Cabal deps name (C.synopsis pd) version
+
+collectDeps :: Maybe (C.CondTree v [C.Dependency] a) -> [C.Dependency]
+collectDeps Nothing = []
+collectDeps (Just (C.CondNode _ deps ifs)) = deps ++ concatMap f ifs
+  where
+    f (C.CondBranch _ t mt) = collectDeps (Just t) ++ collectDeps mt