rebased on master, adressed nicks comments

eras/shelley-ma/impl/src/Cardano/Ledger/ShelleyMA/Rules/Utxo.hs

@@ -343,7 +343,6 @@ utxoTransition = do
   pure
     Shelley.UTxOState
       { Shelley._utxo = eval ((txins @era txb ⋪ utxo) ∪ utxoAdd),
-        -- Domain exclusion (a ⋪ b) deletes 'a' from the domain of 'b'
         Shelley._deposited = deposits' <> depositChange,
         Shelley._fees = fees <> getField @"txfee" txb,
         Shelley._ppups = ppup',

eras/shelley/impl/src/Cardano/Ledger/Shelley/LedgerState.hs

@@ -76,7 +76,6 @@ module Cardano.Ledger.Shelley.LedgerState
     stakeDistr,
     incrementalStakeDistr,
     updateStakeDistribution,
-    resolveIncrementalPtrs,
     aggregateUtxoCoinByCredential,
     applyRUpd,
     applyRUpd',
@@ -147,7 +146,7 @@ import Cardano.Ledger.Keys
   )
 import Cardano.Ledger.PoolDistr (PoolDistr (..))
 import Cardano.Ledger.SafeHash (HashAnnotated, extractHash, hashAnnotated)
-import Cardano.Ledger.Serialization (decodeRecordNamedT, mapToCBOR)
+import Cardano.Ledger.Serialization (decodeRecordNamedT, mapFromCBOR, mapToCBOR)
 import Cardano.Ledger.Shelley.Address.Bootstrap
   ( BootstrapWitness (..),
     bootstrapWitKeyHash,
@@ -576,7 +575,15 @@ pvCanFollow (ProtVer m n) (SJust (ProtVer m' n')) =
 
 -- =============================
 
--- | Incremental Stake, Stake along with possible missed coins from danging Ptrs
+-- | Incremental Stake, Stake along with possible missed coins from danging Ptrs.
+--   Transactions can use Ptrs to refer to a stake credential in a TxOut. The Ptr
+--   does not have to point to anything until the epoch boundary, when we compute
+--   rewards and aggregate staking information for ranking. This is unusual but legal.
+--   In a non incremental system, we use what ever 'legal' Ptrs exist at the epoch
+--   boundary. Here we are computing things incrementally, so we need to remember Ptrs
+--   that might point to something by the time the epoch boundary is reached. When
+--   the epoch boundary is reached we 'resolve' these pointers, to see if any have
+--   become non-dangling since the time they came into the incremental computation.
 data IncrementalStake crypto = IStake
   { credMap :: !(Map (Credential 'Staking crypto) Coin),
     ptrMap :: !(Map Ptr Coin)
@@ -587,10 +594,11 @@ instance CC.Crypto crypto => ToCBOR (IncrementalStake crypto) where
   toCBOR (IStake st dangle) =
     encodeListLen 2 <> mapToCBOR st <> mapToCBOR dangle
 
-instance CC.Crypto crypto =>  FromSharedCBOR (IncrementalStake crypto) where
+instance CC.Crypto crypto => FromSharedCBOR (IncrementalStake crypto) where
+  type Share (IncrementalStake crypto) = Interns (Credential 'Staking crypto)
   fromSharedCBOR credInterns = do
     decodeRecordNamed "Stake" (const 2) $ do
-      stake <- fromSharedCBOR credInterns
+      stake <- fromSharedCBOR (credInterns, mempty)
       dangle <- mapFromCBOR
       pure $ IStake stake dangle
 
@@ -674,7 +682,6 @@ instance
       _stakeDistro <- fromSharedCBOR credInterns
       pure UTxOState {_utxo, _deposited, _fees, _ppups, _stakeDistro}
 
-
 -- | New Epoch state and environment
 data NewEpochState era = NewEpochState
   { -- | Last epoch
@@ -1112,7 +1119,13 @@ stakeDistr u ds ps =
     activeDelegs :: Map (Credential 'Staking (Crypto era)) (KeyHash 'StakePool (Crypto era))
     activeDelegs = eval ((dom rewards' ◁ delegs) ▷ dom poolParams)
 
--- A TxOut has 4 different shapes, depending on the shape of it's embedded Addr.
+compactCoinOrError :: Coin -> CompactForm Coin
+compactCoinOrError c =
+  case toCompact c of
+    Nothing -> error $ "Invalid ADA value in staking: " <> show c
+    Just compactCoin -> compactCoin
+
+-- A TxOut has 4 different shapes, depending on the shape of its embedded Addr.
 -- Credentials are stored in only 2 of the 4 cases.
 -- 1) TxOut (Addr _ _ (StakeRefBase cred)) coin   -> HERE
 -- 2) TxOut (Addr _ _ (StakeRefPtr ptr)) coin     -> HERE
@@ -1188,27 +1201,22 @@ incrementalAggregateUtxoCoinByCredential mode (UTxO u) initial =
             Addr _ _ (StakeRefBase hk) -> IStake (Map.alter (keepOrDelete c) hk stake) ptrs
             _other -> ans
 
--- | Resolve inserts and deletes which were indexed by Ptrs, by looking them up in 'ptrs'
---   and combining them with the ordinary stake. Zero out the Ptr indexed stake in the result.
---   This function is meant to only be called at the Epoch boundary in the Snap Rule. It is not meant
---   to be used to transform the IncrementalStake.
-resolveIncrementalPtrs :: Map Ptr (Credential 'Staking (Crypto era)) -> IncrementalStake (Crypto era) -> IncrementalStake (Crypto era)
-resolveIncrementalPtrs ptrs (IStake stake byPtr) = IStake (Map.foldlWithKey' accum stake byPtr) Map.empty
+-- | Resolve inserts and deletes which were indexed by Ptrs, by looking them
+--   up in 'ptrs' and combining the result of the lookup with the ordinary stake.
+--   Return just this resolved map with type: Map (Credential 'Staking crypto) Coin
+resolveIncrementalPtrs ::
+  Map Ptr (Credential 'Staking (Crypto era)) ->
+  IncrementalStake (Crypto era) ->
+  Map (Credential 'Staking (Crypto era)) Coin
+resolveIncrementalPtrs ptrs (IStake stake byPtr) = Map.foldlWithKey' accum stake byPtr
   where
     accum ans ptr coin =
       case Map.lookup ptr ptrs of
         Nothing -> ans
         Just hash -> Map.insertWith (<>) hash coin ans
 
-compactCoinOrError :: Coin -> CompactForm Coin
-compactCoinOrError c =
-  case toCompact c of
-    Nothing -> error $ "Invalid ADA value in staking: " <> show c
-    Just compactCoin -> compactCoin
-
 -- | Compute the current state distribution by using the IncrementalStake, which is an aggregate
---   of the current UTxO. This function has a non-incremental analog 'takeDistr'
---   analog 'aggregateUtxoCoinByCredential'
+--   of the current UTxO. This function has a non-incremental analog 'stakeDistr'
 incrementalStakeDistr ::
   forall era.
   IncrementalStake (Crypto era) ->
@@ -1224,7 +1232,7 @@ incrementalStakeDistr incstake ds ps =
     DState rewards' delegs bimap _ _ _ = ds
     PState poolParams _ _ = ps
     stake0, stake1 :: Map (Credential 'Staking (Crypto era)) Coin
-    (IStake stake0 _) = resolveIncrementalPtrs @era (forwards bimap) incstake
+    stake0 = resolveIncrementalPtrs @era (forwards bimap) incstake
     stake1 = Map.unionWith (<>) stake0 rewards'
     activeDelegs :: Map (Credential 'Staking (Crypto era)) (KeyHash 'StakePool (Crypto era))
     activeDelegs = eval ((dom rewards' ◁ delegs) ▷ dom poolParams)

eras/shelley/test-suite/src/Test/Cardano/Ledger/Shelley/Address/Bootstrap.hs

@@ -158,7 +158,7 @@ utxoState0 =
       _deposited = Coin 0,
       _fees = Coin 0,
       _ppups = PPUPState (ProposedPPUpdates mempty) (ProposedPPUpdates mempty),
-      _stakeDistro = IStake mempty mempty
+      _stakeDistro = mempty
     }
 
 tx :: Tx C

eras/shelley/test-suite/src/Test/Cardano/Ledger/Shelley/BenchmarkFunctions.hs

@@ -56,7 +56,6 @@ import Cardano.Ledger.Shelley.Delegation.Certificates (DelegCert (..))
 import Cardano.Ledger.Shelley.LedgerState
   ( AccountState (..),
     DPState,
-    IncrementalStake (..),
     UTxOState (..),
   )
 import Cardano.Ledger.Shelley.PParams (PParams, PParams' (..), emptyPParams)
@@ -155,7 +154,7 @@ initUTxO n =
     (Coin 0)
     (Coin 0)
     def
-    (IStake mempty mempty)
+    mempty
 
 -- Protocal Parameters used for the benchmarknig tests.
 -- Note that the fees and deposits are set to zero for

eras/shelley/test-suite/src/Test/Cardano/Ledger/Shelley/Examples/Consensus.hs

@@ -325,7 +325,7 @@ exampleNewEpochState value ppp pp =
                       _deposited = Coin 1000,
                       _fees = Coin 1,
                       _ppups = def,
-                      _stakeDistro = IStake mempty mempty -- Maybe this needs to agree with _utxo?
+                      _stakeDistro = mempty
                     },
                 _delegationState = def
               },