Remove dangling VRFs from set of known VRFs in PoolReap

Author: teodanciu

eras/shelley/impl/src/Cardano/Ledger/Shelley/Rules/PoolReap.hs

@@ -48,6 +48,7 @@ import Control.State.Transition (
  )
 import Data.Default (Default, def)
 import Data.Foldable (fold)
+import qualified Data.Map.Merge.Strict as Map
 import qualified Data.Map.Strict as Map
 import Data.Set (Set)
 import qualified Data.Set as Set
@@ -128,6 +129,20 @@ poolReapTransition = do
   TRC (_, PoolreapState us a cs0, e) <- judgmentContext
   let
     ps0 = cs0 ^. certPStateL
+    -- find the set of VRF keys that are no longer relevant, since they have been overwritten
+    -- via pool re-registration
+    danglingVrfs =
+      Set.fromList $
+        Map.elems $
+          Map.merge
+            Map.dropMissing
+            Map.dropMissing
+            ( Map.zipWithMaybeMatched $ \_ sps spsF ->
+                if sps ^. spsVrfL /= spsF ^. spsVrfL then Just (sps ^. spsVrfL) else Nothing
+            )
+            (ps0 ^. psStakePoolsL)
+            (ps0 ^. psFutureStakePoolsL)
+
     -- activate future stakePools
     ps =
       ps0
@@ -202,7 +217,8 @@ poolReapTransition = do
           & certPStateL . psStakePoolsL %~ (`Map.withoutKeys` retired)
           & certPStateL . psRetiringL %~ (`Map.withoutKeys` retired)
           & certPStateL . psDepositsCompactL .~ remainingDeposits
-          & certPStateL . psVRFKeyHashesL %~ (`Set.difference` retiredVRFs)
+          & certPStateL . psVRFKeyHashesL
+            %~ (\s -> (s `Set.difference` retiredVRFs) `Set.difference` danglingVrfs)
       )
 
 renderPoolReapViolation ::