Byron: move tip block number into ByronTransition

Initial motivation for this is the need (in a later commit) to implement the
translation of the last *ticked* Byron ledger state to the first Shelley state,
which becomes possible as `ByronTransition` is part of the ticked Byron ledger
state.

Apart from the translation to Shelley, this tip block number is only used to
check whether an update proposal became stable, so it makes sense to make it
part of `ByronTransition` in any case.

ouroboros-consensus-cardano/src/byron/Ouroboros/Consensus/Byron/Ledger/Ledger.hs

@@ -89,27 +89,30 @@ import           Ouroboros.Consensus.Util (ShowProxy (..), (..:))
 -------------------------------------------------------------------------------}
 
 data instance LedgerState ByronBlock = ByronLedgerState {
-      byronLedgerTipBlockNo :: !(WithOrigin BlockNo)
-    , byronLedgerState      :: !CC.ChainValidationState
+      byronLedgerState      :: !CC.ChainValidationState
     , byronLedgerTransition :: !ByronTransition
     }
   deriving (Eq, Show, Generic, NoThunks)
 
 -- | Information required to determine the transition from Byron to Shelley
-data ByronTransition =
-    -- | Per candidate proposal, the 'BlockNo' in which it became a candidate
-    --
-    -- The HFC needs to know when a candidate proposal becomes stable. We cannot
-    -- reliably do this using 'SlotNo': doing so would mean that if we were to
-    -- switch to a denser fork, something that was previously deemed stable is
-    -- suddenly not deemed stable anymore (although in actuality it still is).
-    -- We therefore must do this based on 'BlockNo' instead, but unfortunately
-    -- the Byron ledger does not record this information. Therefore, we record
-    -- it here instead.
-    --
-    -- Invariant: the domain of this map should equal the set of candidate
-    -- proposals.
-    ByronTransitionInfo !(Map Update.ProtocolVersion BlockNo)
+data ByronTransition = ByronTransitionInfo {
+      -- | Per candidate proposal, the 'BlockNo' in which it became a candidate
+      --
+      -- The HFC needs to know when a candidate proposal becomes stable. We
+      -- cannot reliably do this using 'SlotNo': doing so would mean that if we
+      -- were to switch to a denser fork, something that was previously deemed
+      -- stable is suddenly not deemed stable anymore (although in actuality it
+      -- still is). We therefore must do this based on 'BlockNo' instead, but
+      -- unfortunately the Byron ledger does not record this information.
+      -- Therefore, we record it here instead.
+      --
+      -- Invariant: the domain of this map should equal the set of candidate
+      -- proposals.
+      perCandidateProposals :: !(Map Update.ProtocolVersion BlockNo)
+    , -- | Block number of the last applied block, used to compute when a
+      -- proposal got stable.
+      byronLedgerTipBlockNo :: !(WithOrigin BlockNo)
+    }
   deriving (Eq, Show, Generic, NoThunks)
 
 instance UpdateLedger ByronBlock
@@ -121,8 +124,7 @@ initByronLedgerState :: Gen.Config
                      -> LedgerState ByronBlock
 initByronLedgerState genesis mUtxo = ByronLedgerState {
       byronLedgerState      = override mUtxo initState
-    , byronLedgerTipBlockNo = Origin
-    , byronLedgerTransition = ByronTransitionInfo Map.empty
+    , byronLedgerTransition = ByronTransitionInfo Map.empty Origin
     }
   where
     initState :: CC.ChainValidationState
@@ -249,7 +251,7 @@ instance LedgerSupportsProtocol ByronBlock where
   --
   -- To create a forecast, take the delegation state from the given ledger
   -- state, and apply the updates that should be applied by the given slot.
-  ledgerViewForecastAt cfg (ByronLedgerState _tipBlkNo st _) = Forecast at $ \for ->
+  ledgerViewForecastAt cfg (ByronLedgerState st _) = Forecast at $ \for ->
       toTickedPBftLedgerView <$> if
         | for == lastSlot ->
           return $ CC.getDelegationMap st
@@ -358,19 +360,23 @@ applyABlock validationMode cfg blk blkHash blkNo TickedByronLedgerState{..} = do
             aux candidate = (UPE.cpuProtocolVersion candidate, blkNo)
 
         transition' :: ByronTransition
-        transition' =
-            case untickedByronLedgerTransition of
-              ByronTransitionInfo oldEntries -> ByronTransitionInfo $
+        transition' = ByronTransitionInfo {
+              perCandidateProposals =
                 -- Candidates that have /just/ become candidates
                 let newEntries :: Map Update.ProtocolVersion BlockNo
                     newEntries = ifNew `Map.difference` oldEntries
 
                 -- Remove any entries that aren't candidates anymore
                 in (oldEntries `Map.intersection` ifNew) `Map.union` newEntries
+            , byronLedgerTipBlockNo = NotOrigin blkNo
+            }
+          where
+            ByronTransitionInfo {
+                perCandidateProposals = oldEntries
+              } = untickedByronLedgerTransition
 
     return ByronLedgerState {
-          byronLedgerTipBlockNo = NotOrigin blkNo
-        , byronLedgerState      = st'
+          byronLedgerState      = st'
         , byronLedgerTransition = transition'
         }
 
@@ -386,9 +392,10 @@ applyABoundaryBlock :: Gen.Config
 applyABoundaryBlock cfg blk blkNo TickedByronLedgerState{..} = do
     st' <- CC.validateBoundary cfg blk tickedByronLedgerState
     return ByronLedgerState {
-        byronLedgerTipBlockNo = NotOrigin blkNo
-      , byronLedgerState      = st'
-      , byronLedgerTransition = untickedByronLedgerTransition
+        byronLedgerState      = st'
+      , byronLedgerTransition = untickedByronLedgerTransition {
+            byronLedgerTipBlockNo = NotOrigin blkNo
+          }
       }
 
 {-------------------------------------------------------------------------------
@@ -412,7 +419,7 @@ encodeByronHeaderState = encodeHeaderState
     encodeByronChainDepState
     encodeByronAnnTip
 
--- | Encode transition info
+-- | Encode candidate proposals (in 'ByronTransition').
 --
 -- We encode the absence of any info separately. This gives us a bit more
 -- wiggle room to change our mind about what we store in snapshots, as they
@@ -422,8 +429,8 @@ encodeByronHeaderState = encodeHeaderState
 -- inclusion of a list length. We didn't, so the decoder is a bit awkward :/
 --
 -- TODO: If we break compatibility anyway, we might decide to clean this up.
-encodeByronTransition :: ByronTransition -> Encoding
-encodeByronTransition (ByronTransitionInfo bNos)
+encodeByronCandidateProposals :: Map Update.ProtocolVersion BlockNo -> Encoding
+encodeByronCandidateProposals bNos
   | Map.null bNos = CBOR.encodeWord8 0
   | otherwise     =
          CBOR.encodeListLen (fromIntegral (Map.size bNos))
@@ -438,13 +445,13 @@ encodeByronTransition (ByronTransitionInfo bNos)
         , encode bno
         ]
 
--- | Decode Byron transition info
+-- | Decode candidate proposals (in 'ByronTransition')
 --
 -- See comments for 'encodeByronTransition'.
-decodeByronTransition :: Decoder s ByronTransition
-decodeByronTransition = do
+decodeByronCandidateProposals :: Decoder s (Map Update.ProtocolVersion BlockNo)
+decodeByronCandidateProposals = do
     ttype <- CBOR.peekTokenType
-    fmap ByronTransitionInfo $ case ttype of
+    case ttype of
       CBOR.TypeUInt -> do
         tag <- CBOR.decodeWord8
         case tag of
@@ -470,16 +477,19 @@ encodeByronLedgerState ByronLedgerState{..} = mconcat [
       encodeListLen 3
     , encode byronLedgerTipBlockNo
     , encode byronLedgerState
-    , encodeByronTransition byronLedgerTransition
+    , encodeByronCandidateProposals perCandidateProposals
     ]
+  where
+    ByronTransitionInfo{..} = byronLedgerTransition
 
 decodeByronLedgerState :: Decoder s (LedgerState ByronBlock)
 decodeByronLedgerState = do
     enforceSize "ByronLedgerState" 3
-    ByronLedgerState
-      <$> decode
-      <*> decode
-      <*> decodeByronTransition
+    tipBlockNo         <- decode
+    ledgerState        <- decode
+    candidateProposals <- decodeByronCandidateProposals
+    let transitionInfo = ByronTransitionInfo candidateProposals tipBlockNo
+    pure $ ByronLedgerState ledgerState transitionInfo
 
 encodeByronQuery :: BlockQuery ByronBlock result -> Encoding
 encodeByronQuery query = case query of

ouroboros-consensus-cardano/src/ouroboros-consensus-cardano/Ouroboros/Consensus/Cardano/CanHardFork.hs

@@ -139,7 +139,7 @@ byronTransition ByronPartialLedgerConfig{..} shelleyMajorVersion state =
     . Byron.Inspect.protocolUpdates byronLedgerConfig
     $ state
   where
-    ByronTransitionInfo transitionInfo = byronLedgerTransition state
+    ByronTransitionInfo transitionInfo _tipBlockNo = byronLedgerTransition state
 
     genesis = byronLedgerConfig
     k       = CC.Genesis.gdK $ CC.Genesis.configGenesisData genesis
@@ -192,7 +192,7 @@ byronTransition ByronPartialLedgerConfig{..} shelleyMajorVersion state =
     isReallyStable (BlockNo bno) = distance >= CC.unBlockCount k
       where
         distance :: Word64
-        distance = case byronLedgerTipBlockNo state of
+        distance = case byronLedgerTipBlockNo $ byronLedgerTransition state of
                      Origin                  -> bno + 1
                      NotOrigin (BlockNo tip) -> tip - bno
 
@@ -393,7 +393,7 @@ translateLedgerStateByronToShelleyWrapper =
         shelleyLedgerTip =
           translatePointByronToShelley
             (ledgerTipPoint ledgerByron)
-            (byronLedgerTipBlockNo ledgerByron)
+            (byronLedgerTipBlockNo $ byronLedgerTransition ledgerByron)
       , shelleyLedgerState =
           SL.translateToShelleyLedgerState
             (toFromByronTranslationContext (shelleyLedgerGenesis cfgShelley))

ouroboros-consensus-cardano/src/unstable-byron-testlib/Test/Consensus/Byron/Examples.hs

@@ -168,9 +168,8 @@ exampleChainDepState = S.fromList signers
 
 emptyLedgerState :: LedgerState ByronBlock
 emptyLedgerState = ByronLedgerState {
-      byronLedgerTipBlockNo = Origin
-    , byronLedgerState      = initState
-    , byronLedgerTransition = ByronTransitionInfo Map.empty
+      byronLedgerState      = initState
+    , byronLedgerTransition = ByronTransitionInfo Map.empty Origin
     }
   where
     initState :: CC.Block.ChainValidationState

ouroboros-consensus-cardano/src/unstable-byron-testlib/Test/Consensus/Byron/Generators.hs

@@ -260,10 +260,12 @@ instance Arbitrary CC.Del.Map where
   arbitrary = CC.Del.fromList <$> arbitrary
 
 instance Arbitrary ByronTransition where
-  arbitrary = ByronTransitionInfo . Map.fromList <$> arbitrary
+  arbitrary = ByronTransitionInfo
+    <$> (Map.fromList <$> arbitrary)
+    <*> arbitrary
 
 instance Arbitrary (LedgerState ByronBlock) where
-  arbitrary = ByronLedgerState <$> arbitrary <*> arbitrary <*> arbitrary
+  arbitrary = ByronLedgerState <$> arbitrary <*> arbitrary
 
 instance Arbitrary (TipInfoIsEBB ByronBlock) where
   arbitrary = TipInfoIsEBB <$> arbitrary <*> elements [IsEBB, IsNotEBB]