fix exponential implementation of transitiveDependencies

Author: MaximilianAlgehed

src/Constrained/Graph.hs

@@ -128,11 +128,12 @@ irreflexiveDependencyOn xs ys =
 
 -- | Get all down-stream dependencies of a node
 transitiveDependencies :: Ord node => node -> Graph node -> Set node
-transitiveDependencies x (Graph e _) = go (Set.singleton x) x
+transitiveDependencies x (Graph e _) = go mempty (Set.toList $ fromMaybe mempty $ Map.lookup x e)
   where
-    go seen y = ys <> foldMap (go $ Set.insert y seen) (Set.difference ys seen)
-      where
-        ys = fromMaybe mempty (Map.lookup y e)
+    go deps [] = deps
+    go deps (y:ys)
+      | y `Set.member` deps = go deps ys
+      | otherwise = go (Set.insert y deps) (ys ++ Set.toList (fromMaybe mempty $ Map.lookup y e))
 
 -- | Take the transitive closure of the graph
 transitiveClosure :: Ord node => Graph node -> Graph node