remove renundant UseDeps

this fix is optimistic due it not check if package versions really
equal. And all code require some tuning

Merge/Dependencies.hs

@@ -98,12 +98,16 @@ resolveDependencies :: Portage.Overlay -> PackageDescription -> Maybe CompilerId
 resolveDependencies overlay pkg mcompiler =
     edeps
       {
-        dep  = Portage.simplify_deps ( dep edeps),
-        rdep = Portage.simplify_deps (rdep edeps)
+        dep  = dep2,
+        rdep = rdep2
         -- todo: if rdep includes cabal or ghc, make sure it's the same
         -- version as in dep
       }
   where
+    dep1  = Portage.simplify_deps ( dep edeps)
+    dep2  = Portage.simplifyUseDeps dep1 (dep1++rdep2)
+    rdep1  = Portage.simplify_deps (rdep edeps)
+    rdep2  = Portage.simplifyUseDeps rdep1 rdep1
     compiler = maybe (fst GHCCore.defaultGHC) id mcompiler
 
     hasBuildableExes p = any (buildable . buildInfo) . executables $ p

Portage/Dependency.hs

@@ -1,6 +1,7 @@
 module Portage.Dependency (
   Dependency(..),
   simplify_deps,
+  simplifyUseDeps,
   addDepUseFlag
   ) where
 
@@ -13,7 +14,7 @@ import Portage.PackageId
 import qualified Text.PrettyPrint as Disp
 import Text.PrettyPrint ( (<>), hsep )
 
-import Data.Maybe ( fromJust, catMaybes )
+import Data.Maybe ( fromJust, catMaybes, mapMaybe )
 import Data.List ( nub, groupBy, partition, sortBy )
 import Data.Ord           (comparing)
 
@@ -189,3 +190,30 @@ addDepUseFlag (OrEarlierVersionOf v p u) n = OrEarlierVersionOf v p (n:u)
 addDepUseFlag (ThisMajorOf v p u) n = ThisMajorOf v p (n:u)
 addDepUseFlag (DependEither d) n = DependEither $ map (flip addDepUseFlag n) d
 addDepUseFlag (DependIfUse u d) n = DependIfUse u (addDepUseFlag d n)
+
+--
+-- | remove all Use dependencies that overlap with normal dependencies
+simplifyUseDeps :: [Dependency]         -- list where use deps is taken
+                    -> [Dependency]     -- list where common deps is taken
+                    -> [Dependency]     -- result deps
+simplifyUseDeps ds cs =
+    let (u,o) = partition isUseDep ds
+        c = mapMaybe getPackage cs
+    in (mapMaybe (intersectD c) u)++o
+
+intersectD :: [PackageName] -> Dependency -> Maybe Dependency
+intersectD fs (DependIfUse u d) = intersectD fs d >>= Just . DependIfUse u
+intersectD fs (DependEither ds) =
+    let ds' = mapMaybe (intersectD fs) ds
+    in if null ds' then Nothing else Just (DependEither ds')
+intersectD fs (AllOf ds) =
+    let ds' = mapMaybe (intersectD fs) ds
+    in if null ds' then Nothing else Just (AllOf ds')
+intersectD fs x =
+    let pkg = fromJust $ getPackage x -- this is unsafe but will save from error later
+    in if any (==pkg) fs then Nothing else Just x
+
+isUseDep :: Dependency -> Bool
+isUseDep (DependIfUse _ _) = True
+isUseDep _ = False
+--