compute ancestors in graph

src/Juvix/Data/DependencyInfo.hs

@@ -75,3 +75,15 @@ nodesOnCycles = foldr go mempty . buildSCCs
     go x acc = case x of
       CyclicSCC ns -> foldr HashSet.insert acc ns
       _ -> acc
+
+-- | Computes the ancestors of `startNodes`, i.e., the set of nodes from which
+-- some node in `startNodes` is reachable. Complexity O(V + E).
+computeAncestors :: forall n. (Hashable n) => DependencyInfo n -> [n] -> HashSet n
+computeAncestors depInfo startNodes =
+  HashSet.fromList
+    . map (fst . (depInfo ^. depInfoNodeFromVertex))
+    . filter (/= v)
+    $ Graph.reachable graph' v
+  where
+    adjacent = mapMaybe (depInfo ^. depInfoVertexFromName) startNodes
+    (v, graph') = addFreshVertex adjacent (Graph.transposeG (depInfo ^. depInfoGraph))

src/Juvix/Prelude/Base/Foundation.hs

@@ -151,6 +151,7 @@ import Data.Type.Equality (type (~))
 import Data.Typeable hiding (TyCon)
 import Data.Void
 import Data.Word
+import GHC.Arr qualified as Array
 import GHC.Base (assert)
 import GHC.Enum
 import GHC.Err qualified as Err
@@ -661,3 +662,10 @@ zipWithNextLoop l = NonEmpty.reverse (go [] l)
     go acc = \case
       lastA :| [] -> (lastA, h) :| acc
       x :| y : as -> go ((x, y) : acc) (y :| as)
+
+addFreshVertex :: [Vertex] -> Graph -> (Vertex, Graph)
+addFreshVertex adjacent graph =
+  (v, Array.array (lo, v) (Array.assocs graph ++ [(v, adjacent)]))
+  where
+    (lo, hi) = Array.bounds graph
+    v = hi + 1