{-# LANGUAGE DeriveDataTypeable #-} {-# LANGUAGE DeriveGeneric #-} {-# LANGUAGE DeriveFunctor #-} {-# LANGUAGE DeriveFoldable #-} {-# LANGUAGE DeriveTraversable #-} module Distribution.Types.CondTree ( CondTree(..), CondBranch(..), condIfThen, condIfThenElse, mapCondTree, mapTreeConstrs, mapTreeConds, mapTreeData, extractCondition, simplifyCondTree, ignoreConditions, ) where import Prelude () import Distribution.Compat.Prelude import Distribution.Types.Condition -- | A 'CondTree' is used to represent the conditional structure of -- a Cabal file, reflecting a syntax element subject to constraints, -- and then any number of sub-elements which may be enabled subject -- to some condition. Both @a@ and @c@ are usually 'Monoid's. -- -- To be more concrete, consider the following fragment of a @Cabal@ -- file: -- -- @ -- build-depends: base >= 4.0 -- if flag(extra) -- build-depends: base >= 4.2 -- @ -- -- One way to represent this is to have @'CondTree' 'ConfVar' -- ['Dependency'] 'BuildInfo'@. Here, 'condTreeData' represents -- the actual fields which are not behind any conditional, while -- 'condTreeComponents' recursively records any further fields -- which are behind a conditional. 'condTreeConstraints' records -- the constraints (in this case, @base >= 4.0@) which would -- be applied if you use this syntax; in general, this is -- derived off of 'targetBuildInfo' (perhaps a good refactoring -- would be to convert this into an opaque type, with a smart -- constructor that pre-computes the dependencies.) -- data CondTree v c a = CondNode { condTreeData :: a , condTreeConstraints :: c , condTreeComponents :: [CondBranch v c a] } deriving (Show, Eq, Typeable, Data, Generic, Functor, Foldable, Traversable) instance (Binary v, Binary c, Binary a) => Binary (CondTree v c a) -- | A 'CondBranch' represents a conditional branch, e.g., @if -- flag(foo)@ on some syntax @a@. It also has an optional false -- branch. -- data CondBranch v c a = CondBranch { condBranchCondition :: Condition v , condBranchIfTrue :: CondTree v c a , condBranchIfFalse :: Maybe (CondTree v c a) } deriving (Show, Eq, Typeable, Data, Generic, Functor, Traversable) -- This instance is written by hand because GHC 8.0.1/8.0.2 infinite -- loops when trying to derive it with optimizations. See -- https://ghc.haskell.org/trac/ghc/ticket/13056 instance Foldable (CondBranch v c) where foldMap f (CondBranch _ c Nothing) = foldMap f c foldMap f (CondBranch _ c (Just a)) = foldMap f c `mappend` foldMap f a instance (Binary v, Binary c, Binary a) => Binary (CondBranch v c a) condIfThen :: Condition v -> CondTree v c a -> CondBranch v c a condIfThen c t = CondBranch c t Nothing condIfThenElse :: Condition v -> CondTree v c a -> CondTree v c a -> CondBranch v c a condIfThenElse c t e = CondBranch c t (Just e) mapCondTree :: (a -> b) -> (c -> d) -> (Condition v -> Condition w) -> CondTree v c a -> CondTree w d b mapCondTree fa fc fcnd (CondNode a c ifs) = CondNode (fa a) (fc c) (map g ifs) where g (CondBranch cnd t me) = CondBranch (fcnd cnd) (mapCondTree fa fc fcnd t) (fmap (mapCondTree fa fc fcnd) me) mapTreeConstrs :: (c -> d) -> CondTree v c a -> CondTree v d a mapTreeConstrs f = mapCondTree id f id mapTreeConds :: (Condition v -> Condition w) -> CondTree v c a -> CondTree w c a mapTreeConds f = mapCondTree id id f mapTreeData :: (a -> b) -> CondTree v c a -> CondTree v c b mapTreeData f = mapCondTree f id id -- | Extract the condition matched by the given predicate from a cond tree. -- -- We use this mainly for extracting buildable conditions (see the Note above), -- but the function is in fact more general. extractCondition :: Eq v => (a -> Bool) -> CondTree v c a -> Condition v extractCondition p = go where go (CondNode x _ cs) | not (p x) = Lit False | otherwise = goList cs goList [] = Lit True goList (CondBranch c t e : cs) = let ct = go t ce = maybe (Lit True) go e in ((c `cAnd` ct) `cOr` (CNot c `cAnd` ce)) `cAnd` goList cs -- | Flattens a CondTree using a partial flag assignment. When a condition -- cannot be evaluated, both branches are ignored. simplifyCondTree :: (Monoid a, Monoid d) => (v -> Either v Bool) -> CondTree v d a -> (d, a) simplifyCondTree env (CondNode a d ifs) = mconcat $ (d, a) : mapMaybe simplifyIf ifs where simplifyIf (CondBranch cnd t me) = case simplifyCondition cnd env of (Lit True, _) -> Just $ simplifyCondTree env t (Lit False, _) -> fmap (simplifyCondTree env) me _ -> Nothing -- | Flatten a CondTree. This will resolve the CondTree by taking all -- possible paths into account. Note that since branches represent exclusive -- choices this may not result in a \"sane\" result. ignoreConditions :: (Monoid a, Monoid c) => CondTree v c a -> (a, c) ignoreConditions (CondNode a c ifs) = (a, c) `mappend` mconcat (concatMap f ifs) where f (CondBranch _ t me) = ignoreConditions t : maybeToList (fmap ignoreConditions me)