Change type of extraCoinSource from Maybe Coin to Coin.

The following values of `extraCoinSource` are treated identically by the
coin selection algorithm:

    - Nothing
    - Just (Coin 0)

Therefore, using the type `Maybe Coin` doesn't really make sense here.

If a caller wants to encode the lack of an extra coin source, they can
just supply `Coin 0`.

lib/core/src/Cardano/Wallet.hs

@@ -2040,10 +2040,7 @@ migrationPlanToSelectionWithdrawals plan rewardWithdrawal outputAddressesToCycle
         -- and have the transaction layer calculate the actual fee based only
         -- on the contents of that record.
         --
-        extraCoinSource =
-            if (view #rewardWithdrawal migrationSelection) > Coin 0
-            then Just (view #rewardWithdrawal migrationSelection)
-            else Nothing
+        extraCoinSource = view #rewardWithdrawal migrationSelection
 
         withdrawal =
             if (view #rewardWithdrawal migrationSelection) > Coin 0

lib/core/src/Cardano/Wallet/Primitive/CoinSelection.hs

@@ -38,7 +38,7 @@ import Cardano.Wallet.Primitive.CoinSelection.Balance
 import Cardano.Wallet.Primitive.Types.Address
     ( Address )
 import Cardano.Wallet.Primitive.Types.Coin
-    ( Coin )
+    ( Coin (..) )
 import Cardano.Wallet.Primitive.Types.TokenBundle
     ( TokenBundle )
 import Cardano.Wallet.Primitive.Types.TokenMap
@@ -63,6 +63,8 @@ import Data.Generics.Labels
     ()
 import Data.List.NonEmpty
     ( NonEmpty (..) )
+import Data.Maybe
+    ( fromMaybe )
 import Data.Word
     ( Word16 )
 import GHC.Generics
@@ -112,7 +114,7 @@ performSelection selectionConstraints selectionParams =
                 Balance.SelectionParams
                     { assetsToBurn
                     , assetsToMint
-                    , extraCoinSource = rewardWithdrawal
+                    , extraCoinSource = fromMaybe (Coin 0) rewardWithdrawal
                     , outputsToCover = preparedOutputsToCover
                     , selectionLimit =
                         computeSelectionLimit $ F.toList preparedOutputsToCover

lib/core/src/Cardano/Wallet/Primitive/CoinSelection/Balance.hs

@@ -227,8 +227,8 @@ data SelectionParams = SelectionParams
         :: !SelectionLimit
         -- ^ Specifies a limit to be adhered to when performing selection.
     , extraCoinSource
-        :: !(Maybe Coin)
-        -- ^ An optional extra source of ada.
+        :: !Coin
+        -- ^ An extra source of ada.
     , assetsToMint
         :: !TokenMap
         -- ^ Assets to mint: these provide input value to a transaction.
@@ -287,7 +287,7 @@ computeUTxOBalanceRequired params =
     balanceIn =
         TokenBundle.fromTokenMap (view #assetsToMint params)
         `TokenBundle.add`
-        F.foldMap TokenBundle.fromCoin (view #extraCoinSource params)
+        TokenBundle.fromCoin (view #extraCoinSource params)
     balanceOut =
         TokenBundle.fromTokenMap (view #assetsToBurn params)
         `TokenBundle.add`
@@ -386,8 +386,8 @@ data SelectionResult change = SelectionResult
         :: !(NonEmpty (TxIn, TxOut))
         -- ^ A (non-empty) list of inputs selected from 'utxoAvailable'.
     , extraCoinSource
-        :: !(Maybe Coin)
-        -- ^ An optional extra source of ada.
+        :: !Coin
+        -- ^ An extra source of ada.
     , outputsCovered
         :: ![TxOut]
         -- ^ A list of outputs covered.
@@ -459,7 +459,7 @@ selectionDeltaAllAssets result
     balanceIn =
         TokenBundle.fromTokenMap assetsToMint
         `TokenBundle.add`
-        F.foldMap TokenBundle.fromCoin extraCoinSource
+        TokenBundle.fromCoin extraCoinSource
         `TokenBundle.add`
         F.foldMap (view #tokens . snd) inputsSelected
     balanceOut =
@@ -924,7 +924,7 @@ data SelectionReportSummarized = SelectionReportSummarized
     , totalAdaBalanceIn :: Coin
     , totalAdaBalanceOut :: Coin
     , adaBalanceOfSelectedInputs :: Coin
-    , adaBalanceOfExtraInput :: Coin
+    , adaBalanceOfExtraCoinSource :: Coin
     , adaBalanceOfRequestedOutputs :: Coin
     , adaBalanceOfGeneratedChangeOutputs :: Coin
     , numberOfSelectedInputs :: Int
@@ -967,13 +967,13 @@ makeSelectionReportSummarized s = SelectionReportSummarized {..}
     computedFee
         = Coin.distance totalAdaBalanceIn totalAdaBalanceOut
     totalAdaBalanceIn
-        = adaBalanceOfSelectedInputs <> adaBalanceOfExtraInput
+        = adaBalanceOfSelectedInputs <> adaBalanceOfExtraCoinSource
     totalAdaBalanceOut
         = adaBalanceOfGeneratedChangeOutputs <> adaBalanceOfRequestedOutputs
     adaBalanceOfSelectedInputs
         = F.foldMap (view (#tokens . #coin) . snd) $ view #inputsSelected s
-    adaBalanceOfExtraInput
-        = F.fold (view #extraCoinSource s)
+    adaBalanceOfExtraCoinSource
+        = view #extraCoinSource s
     adaBalanceOfGeneratedChangeOutputs
         = F.foldMap (view #coin) $ view #changeGenerated s
     adaBalanceOfRequestedOutputs
@@ -1265,8 +1265,8 @@ data MakeChangeCriteria minCoinFor bundleSizeAssessor = MakeChangeCriteria
       --          - getCoin (fold changeBundles)
       --
       -- This typically captures fees plus key deposits.
-    , extraCoinSource :: Maybe Coin
-        -- ^ An optional extra source of ada.
+    , extraCoinSource :: Coin
+        -- ^ An extra source of ada.
     , inputBundles :: NonEmpty TokenBundle
         -- ^ Token bundles of selected inputs.
     , outputBundles :: NonEmpty TokenBundle
@@ -1464,7 +1464,7 @@ makeChange criteria
     totalInputValue :: TokenBundle
     totalInputValue =
         F.fold inputBundles
-            <> F.foldMap TokenBundle.fromCoin extraCoinSource
+            <> TokenBundle.fromCoin extraCoinSource
             -- Mints represent extra inputs from "the void"
             <> TokenBundle.fromTokenMap assetsToMint
 

lib/core/test/unit/Cardano/Wallet/Primitive/CoinSelection/BalanceSpec.hs

@@ -186,7 +186,6 @@ import Test.QuickCheck
     , genericShrink
     , ioProperty
     , label
-    , oneof
     , property
     , shrinkList
     , suchThat
@@ -625,7 +624,7 @@ genSelectionParams genUTxOIndex' = do
             (1, UTxOIndex.size utxoAvailable `div` 8)
           )
         ]
-    extraCoinSource <- oneof [ pure Nothing, Just <$> genCoin ]
+    extraCoinSource <- genCoin
     (assetsToMint, assetsToBurn) <- genAssetsToMintAndBurn utxoAvailable
     pure $ SelectionParams
         { outputsToCover
@@ -1526,7 +1525,7 @@ encodeBoundaryTestCriteria c = SelectionParams
     , selectionLimit =
         NoLimit
     , extraCoinSource =
-        Nothing
+        Coin 0
     , assetsToMint =
         TokenMap.empty
     , assetsToBurn =
@@ -1966,7 +1965,7 @@ isValidMakeChangeData p = (&&)
   where
     totalInputValue =
         F.fold (inputBundles p)
-            <> (F.foldMap TokenBundle.fromCoin (view #extraCoinSource p))
+            <> (TokenBundle.fromCoin (view #extraCoinSource p))
             <> TokenBundle.fromTokenMap (view #assetsToMint p)
     totalOutputValue =
         F.fold (outputBundles p)
@@ -1980,8 +1979,8 @@ genMakeChangeData = flip suchThat isValidMakeChangeData $ do
     MakeChangeCriteria
         <$> arbitrary
         <*> pure NoBundleSizeLimit
-        <*> genCoin
-        <*> oneof [pure Nothing, Just <$> genCoinPositive]
+        <*> genRequiredCost
+        <*> genExtraCoinSource
         <*> genTokenBundles inputBundleCount
         <*> genTokenBundles outputBundleCount
         <*> genAssetsToMint
@@ -1993,6 +1992,12 @@ genMakeChangeData = flip suchThat isValidMakeChangeData $ do
     genAssetsToBurn :: Gen TokenMap
     genAssetsToBurn = genTokenMapSmallRange
 
+    genExtraCoinSource :: Gen Coin
+    genExtraCoinSource = genCoin
+
+    genRequiredCost :: Gen Coin
+    genRequiredCost = genCoin
+
     genTokenBundles :: Int -> Gen (NonEmpty TokenBundle)
     genTokenBundles count = (:|)
         <$> genTokenBundleSmallRangePositive
@@ -2015,7 +2020,7 @@ prop_makeChange_identity bundles = (===)
     criteria = MakeChangeCriteria
         { minCoinFor = const (Coin 0)
         , requiredCost = Coin 0
-        , extraCoinSource = Nothing
+        , extraCoinSource = Coin 0
         , bundleSizeAssessor = mkBundleSizeAssessor NoBundleSizeLimit
         , inputBundles = bundles
         , outputBundles = bundles
@@ -2232,7 +2237,7 @@ prop_makeChange_success_delta p change =
         ]
     totalInputValue =
         F.fold (inputBundles p)
-            <> F.foldMap TokenBundle.fromCoin (view #extraCoinSource p)
+            <> TokenBundle.fromCoin (view #extraCoinSource p)
             <> TokenBundle.fromTokenMap (view #assetsToMint p)
     totalInputCoin =
         TokenBundle.getCoin totalInputValue
@@ -2290,7 +2295,7 @@ prop_makeChange_fail_costTooBig p =
   where
     totalInputValue =
         F.fold (inputBundles p)
-            <> F.foldMap TokenBundle.fromCoin (view #extraCoinSource p)
+            <> TokenBundle.fromCoin (view #extraCoinSource p)
             <> TokenBundle.fromTokenMap (view #assetsToMint p)
     totalOutputValue =
         F.fold (outputBundles p)
@@ -2339,7 +2344,7 @@ prop_makeChange_fail_minValueTooBig p =
   where
     totalInputValue =
         F.fold (inputBundles p)
-            <> F.foldMap TokenBundle.fromCoin (view #extraCoinSource p)
+            <> TokenBundle.fromCoin (view #extraCoinSource p)
             <> TokenBundle.fromTokenMap (view #assetsToMint p)
     totalOutputValue =
         F.fold (outputBundles p)
@@ -2366,15 +2371,15 @@ unit_makeChange =
     matrix =
         -- Simple, only ada, should construct a single change output with 1 ada.
         [ ( noMinCoin, noCost
-          , Nothing
+          , Coin 0
           , b 2 [] :| []
           , b 1 [] :| []
           , Right [b 1 []]
           )
 
         -- Two outputs, no cost, changes are proportional, no extra assets
         , ( noMinCoin, noCost
-          , Nothing
+          , Coin 0
           , b 9 [(assetA, 9), (assetB, 6)] :| []
           , b 2 [(assetA, 1)] :| [b 1 [(assetA, 2), (assetB, 3)]]
           , Right
@@ -2386,7 +2391,7 @@ unit_makeChange =
         -- Extra non-user-specified assets. Large assets end up in 'large'
         -- bundles and small extra assets in smaller bundles.
         , ( noMinCoin, noCost
-          , Nothing
+          , Coin 0
           , b 1 [(assetA, 10), (assetC, 1)] :| [b 1 [(assetB, 2), (assetC, 8)]]
           , b 1 [(assetA, 5)] :| [b 1 [(assetB, 1)]]
           , Right

lib/shelley/test/unit/Cardano/Wallet/Shelley/TransactionSpec.hs

@@ -816,7 +816,7 @@ binaryCalculationsSpec' era = describe ("calculateBinary - "+||era||+"") $ do
           Right unsigned = mkUnsignedTx era slotNo cs md mempty [] fee
           cs = SelectionResult
             { inputsSelected = NE.fromList inps
-            , extraCoinSource = Nothing
+            , extraCoinSource = Coin 0
             , outputsCovered = outs
             , changeGenerated = chgs
             , utxoRemaining = UTxOIndex.empty
@@ -897,7 +897,7 @@ makeShelleyTx era testCase = Cardano.makeSignedTransaction addrWits unsigned
     addrWits = map (mkShelleyWitness unsigned) pairs
     cs = SelectionResult
         { inputsSelected = NE.fromList inps
-        , extraCoinSource = Nothing
+        , extraCoinSource = Coin 0
         , outputsCovered = []
         , changeGenerated = outs
         , utxoRemaining = UTxOIndex.empty
@@ -933,7 +933,7 @@ makeByronTx era testCase = Cardano.makeSignedTransaction byronWits unsigned
     byronWits = map (error "makeByronTx: broken") pairs  -- TODO: [ADP-919]
     cs = SelectionResult
         { inputsSelected = NE.fromList inps
-        , extraCoinSource = Nothing
+        , extraCoinSource = Coin 0
         , outputsCovered = []
         , changeGenerated = outs
         , utxoRemaining = UTxOIndex.empty