Handle explicitly the case of no stake or uncomputable ratio

eras/conway/impl/src/Cardano/Ledger/Conway/Rules/Ratify.hs

@@ -60,6 +60,7 @@ data RatifyEnv era = RatifyEnv
   , reDRepDistr :: !(Map (DRep (EraCrypto era)) (CompactForm Coin))
   , reCurrentEpoch :: !EpochNo
   }
+  deriving (Show)
 
 newtype RatifySignal era
   = RatifySignal
@@ -141,11 +142,13 @@ spoAccepted RatifyEnv {reStakePoolDistr = PoolDistr poolDistr} gas =
       HardForkInitiation {} -> 101 % 100
       _ -> spoThreshold
 
-dRepAccepted :: forall era. RatifyEnv era -> GovActionState era -> Bool
-dRepAccepted RatifyEnv {reDRepDistr} GovActionState {gasDRepVotes, gasAction} =
+dRepAccepted :: forall era. RatifyEnv era -> GovActionState era -> Ratio Word64 -> Bool
+dRepAccepted RatifyEnv {reDRepDistr} GovActionState {gasDRepVotes, gasAction} threshold =
   case dRepAcceptedRatio reDRepDistr gasDRepVotes gasAction of
-    Nothing -> True -- TODO: change this when we are ready to consider dReps on sanchonet
-    Just ratio -> ratio >= dRepThreshold
+    Nothing
+      | threshold == 0 -> True
+      | otherwise -> False
+    Just ratio -> ratio >= threshold
 
 -- Compute the dRep ratio yes/(yes + no), where
 -- yes: is the total stake of
@@ -206,7 +209,7 @@ ratifyTransition = do
   case rsig of
     act@(_, ast@GovActionState {gasAction, gasProposedIn}) :<| sigs -> do
       let expired = gasProposedIn + epochsToExpire < reCurrentEpoch
-      if spoAccepted env ast && dRepAccepted env ast
+      if spoAccepted env ast && dRepAccepted env ast dRepThreshold
         then do
           -- Update ENACT state with the governance action that was ratified
           es <- trans @(EraRule "ENACT" era) $ TRC ((), rsEnactState, gasAction)

eras/conway/impl/test/Test/Cardano/Ledger/Conway/RatifySpec.hs

@@ -13,11 +13,13 @@ import Cardano.Ledger.Coin (Coin (..), CompactForm (..))
 import Cardano.Ledger.Conway
 import Cardano.Ledger.Conway.Governance (
   GovAction (..),
+  GovActionState (..),
   Vote (..),
  )
-import Cardano.Ledger.Conway.Rules
+import Cardano.Ledger.Conway.Rules (RatifyEnv (..), dRepAccepted, dRepAcceptedRatio)
 import Cardano.Ledger.Core
 import Data.Foldable (fold)
+import Data.Functor.Identity (Identity)
 import Data.Map.Strict (Map)
 import qualified Data.Map.Strict as Map
 import Data.Maybe (fromMaybe)
@@ -31,6 +33,7 @@ spec :: Spec
 spec = do
   describe "Ratification" $ do
     drepsProp @Conway
+    drepsPropNoStake @Conway
 
 drepsProp :: forall era. Era era => Spec
 drepsProp =
@@ -92,3 +95,21 @@ drepsProp =
             _ -> False
         )
         l
+
+drepsPropNoStake ::
+  forall era.
+  ( EraPParams era
+  , Arbitrary (PParamsHKD StrictMaybe era)
+  , Arbitrary (PParamsHKD Identity era)
+  ) =>
+  Spec
+drepsPropNoStake =
+  prop "If there is no stake, accept only if the threshold is zero" $
+    forAll
+      ((,) <$> arbitrary @(RatifyEnv era) <*> arbitrary @(GovActionState era))
+      ( \(env, gas) -> do
+          dRepAccepted @era env {reDRepDistr = Map.empty} gas 0
+            `shouldBe` True
+          dRepAccepted @era env {reDRepDistr = Map.empty} gas (1 % 2)
+            `shouldBe` False
+      )

eras/conway/impl/testlib/Test/Cardano/Ledger/Conway/Arbitrary.hs

@@ -85,7 +85,7 @@ instance Crypto c => Arbitrary (AlonzoScript (ConwayEra c)) where
   arbitrary = genAlonzoScript [PlutusV1, PlutusV2, PlutusV3]
 
 ------------------------------------------------------------------------------------------
--- Cardano.Ledger.Conway.Gov ------------------------------------------------------
+-- Cardano.Ledger.Conway.Goverance  ------------------------------------------------------
 ------------------------------------------------------------------------------------------
 
 instance
@@ -107,6 +107,17 @@ instance
       <*> arbitrary
       <*> arbitrary
 
+instance
+  (Era era, Arbitrary (PParams era), Arbitrary (PParamsUpdate era)) =>
+  Arbitrary (RatifyEnv era)
+  where
+  arbitrary =
+    RatifyEnv
+      <$> arbitrary
+      <*> arbitrary
+      <*> arbitrary
+      <*> arbitrary
+
 instance Crypto (EraCrypto era) => Arbitrary (Constitution era) where
   arbitrary = Constitution <$> arbitrary <*> arbitrary