Resolve a fixme in head logic

Also fix the compilation after splitting the decommit branch.

hydra-node/src/Hydra/HeadLogic.hs

@@ -29,7 +29,6 @@ import Data.Set ((\\))
 import Data.Set qualified as Set
 import GHC.Records (getField)
 import Hydra.API.ClientInput (ClientInput (..))
-import Hydra.API.HTTPServer (DraftCommitTxRequest (utxoToCommit))
 import Hydra.API.ServerOutput qualified as ServerOutput
 import Hydra.Chain (
   ChainEvent (..),
@@ -89,9 +88,7 @@ import Hydra.Ledger (
   Ledger (..),
   TxIdType,
   UTxOType,
-  ValidationResult (..),
   applyTransactions,
-  canApply,
   txId,
   utxoFromTx,
   withoutUTxO,
@@ -457,16 +454,12 @@ onOpenNetworkReqSn env ledger st otherParty sn requestedTxIds mDecommitTx =
     case mDecommitTx of
       Nothing -> cont (confirmedUTxO, Nothing)
       Just decommitTx ->
-        -- FIXME: Why don't we apply the decommitTx to the confirmed UTxO? Right
-        -- now the inputs would still remain on the L2 state and actually don't
-        -- get removed by 'withoutUTxO' below, because the utxoToCommit are not
-        -- in confirmedUTxO (but the inputs of the decommitTx would be).
-        case canApply ledger currentSlot confirmedUTxO decommitTx of
-          Invalid err ->
+        case applyTransactions ledger currentSlot confirmedUTxO [decommitTx] of
+          Left (_, err) ->
             Error $ RequireFailed $ DecommitDoesNotApply decommitTx err
-          Valid -> do
+          Right newConfirmedUTxO -> do
             let utxoToDecommit = utxoFromTx decommitTx
-            let activeUTxO = confirmedUTxO `withoutUTxO` utxoToDecommit
+            let activeUTxO = newConfirmedUTxO `withoutUTxO` utxoToDecommit
             cont (activeUTxO, Just utxoToDecommit)
 
   -- NOTE: at this point we know those transactions apply on the localUTxO because they

hydra-node/test/Hydra/Chain/Direct/StateSpec.hs

@@ -87,7 +87,7 @@ import Hydra.Chain.Direct.State (
   unsafeObserveInitAndCommits,
  )
 import Hydra.Chain.Direct.State qualified as Transition
-import Hydra.Chain.Direct.Tx (AbortObservation (..), CloseObservation (..), ClosedThreadOutput (closedContesters), CollectComObservation (..), CommitObservation (..), ContestObservation (..), DecrementObservation (..), FanoutObservation (..), HeadObservation (..), IncrementObservation (..), NotAnInitReason (..), observeCommitTx, observeHeadTx, observeInitTx)
+import Hydra.Chain.Direct.Tx (AbortObservation (..), CloseObservation (..), ClosedThreadOutput (closedContesters), CollectComObservation (..), CommitObservation (..), ContestObservation (..), DecrementObservation (..), FanoutObservation (..), HeadObservation (..), NotAnInitReason (..), observeCommitTx, observeHeadTx, observeInitTx)
 import Hydra.ContestationPeriod (toNominalDiffTime)
 import Hydra.Contract.HeadTokens qualified as HeadTokens
 import Hydra.Contract.Initial qualified as Initial