Remove the restriction that all minted assets must be spent or burned.

This commit only makes the minimum amount of changes necessary to ensure
that the code still compiles.

Further work will be required to verify correctness and completeness.

lib/core/src/Cardano/Wallet/Api/Server.hs

@@ -361,7 +361,6 @@ import Cardano.Wallet.Primitive.CoinSelection.Balance
     ( SelectionResult (..)
     , UnableToConstructChangeError (..)
     , balanceMissing
-    , missingOutputAssets
     , selectionDelta
     )
 import Cardano.Wallet.Primitive.Delegation.UTxO
@@ -3821,13 +3820,6 @@ instance IsServerError ErrSelectAssets where
                         , "must specify enough ada. Here are the problematic "
                         , "outputs:\n" <> pretty (indentF 2 $ blockListF xs)
                         ]
-                Balance.OutputsInsufficient e ->
-                    apiError err403 TokensMintedButNotSpentOrBurned $ mconcat
-                        [ "I can't process this transaction because some "
-                        , "minted values were not spent or burned. These "
-                        , "are the values that should be spent or burned: "
-                        , pretty . Flat $ missingOutputAssets e
-                        ]
                 Balance.UnableToConstructChange e ->
                     apiError err403 CannotCoverFee $ T.unwords
                         [ "I am unable to finalize the transaction, as there"

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

@@ -39,7 +39,6 @@ module Cardano.Wallet.Primitive.CoinSelection.Balance
     , SelectionResult (..)
     , SelectionError (..)
     , BalanceInsufficientError (..)
-    , OutputsInsufficientError (..)
     , SelectionInsufficientError (..)
     , InsufficientMinCoinValueError (..)
     , UnableToConstructChangeError (..)
@@ -103,7 +102,6 @@ module Cardano.Wallet.Primitive.CoinSelection.Balance
     , distance
     , mapMaybe
     , balanceMissing
-    , missingOutputAssets
     ) where
 
 import Prelude
@@ -312,55 +310,10 @@ data SelectionError
         SelectionInsufficientError
     | InsufficientMinCoinValues
         (NonEmpty InsufficientMinCoinValueError)
-    | OutputsInsufficient
-        OutputsInsufficientError
     | UnableToConstructChange
         UnableToConstructChangeError
     deriving (Generic, Eq, Show)
 
--- | Indicates that a portion of the minted assets were not spent or burned.
---
--- This situation occurs if the following inequality does not hold:
---
--- >>> assetsToMint `leq` (assetsToBurn <> requestedOutputAssets)
---
--- The existence of this error reflects a deliberate design choice: all minted
--- assets must either be explicitly spent or explicitly burned by the caller.
--- In future, we could revise this design to allow excess minted assets (those
--- that are neither spent nor burned) to be returned to the wallet as change.
---
-data OutputsInsufficientError = OutputsInsufficientError
-    { assetsToMint
-        :: !TokenMap
-      -- ^ The assets to mint
-    , assetsToBurn
-        :: !TokenMap
-      -- ^ The assets to burn
-    , requestedOutputAssets
-        :: !TokenMap
-      -- ^ The complete set of assets found within the user-specified outputs
-    } deriving (Generic, Eq, Show)
-
--- | Computes the portion of minted assets that are not spent or burned.
---
-missingOutputAssets :: OutputsInsufficientError -> TokenMap
-missingOutputAssets e =
-    -- We use 'difference' which will show us the quantities in 'assetsToMint'
-    -- that are not in 'assetsToBurn <> requestedOutputAssets'.
-    --
-    -- Any asset quantity present in 'assetsToBurn <> requestedOutputAssets'
-    -- but not present in 'assetsToMint' will simply be zeroed out, which is
-    -- the behaviour we want for this error report.
-    --
-    assetsToMint `TokenMap.difference`
-        (assetsToBurn `TokenMap.add` requestedOutputAssets)
-  where
-    OutputsInsufficientError
-        { assetsToMint
-        , assetsToBurn
-        , requestedOutputAssets
-        } = e
-
 -- | Indicates that the balance of inputs actually selected was insufficient to
 --   cover the balance of 'outputsToCover'.
 --
@@ -497,11 +450,6 @@ performSelection
         -- ^ The selection goal to satisfy.
     -> m (Either SelectionError (SelectionResult TokenBundle))
 performSelection minCoinFor costFor bundleSizeAssessor criteria
-    -- Is the minted value all spent or burnt?
-    | not (assetsToMint `leq` (assetsToBurn <> requestedOutputAssets)) =
-        pure $ Left $ OutputsInsufficient $ OutputsInsufficientError
-            {assetsToMint, assetsToBurn, requestedOutputAssets}
-
     -- Is the total available balance sufficient?
     | not (balanceRequired `leq` balanceAvailable) =
         pure $ Left $ BalanceInsufficient $ BalanceInsufficientError
@@ -546,7 +494,6 @@ performSelection minCoinFor costFor bundleSizeAssessor criteria
             }
 
     requestedOutputs = F.foldMap (view #tokens) outputsToCover
-    requestedOutputAssets = view #tokens requestedOutputs
 
     mkInputsSelected :: UTxOIndex -> NonEmpty (TxIn, TxOut)
     mkInputsSelected =

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

@@ -27,7 +27,6 @@ import Cardano.Wallet.Primitive.CoinSelection.Balance
     , BalanceInsufficientError (..)
     , InsufficientMinCoinValueError (..)
     , MakeChangeCriteria (..)
-    , OutputsInsufficientError (..)
     , RunSelectionParams (..)
     , SelectionCriteria (..)
     , SelectionError (..)
@@ -54,7 +53,6 @@ import Cardano.Wallet.Primitive.CoinSelection.Balance
     , makeChangeForNonUserSpecifiedAssets
     , makeChangeForUserSpecifiedAsset
     , mapMaybe
-    , missingOutputAssets
     , performSelection
     , prepareOutputsWith
     , reduceTokenQuantities
@@ -745,8 +743,6 @@ prop_performSelection_small minCoinValueFor costFor (Blind (Small criteria)) =
             "selection limited but sufficient"
         . cover 10 (selectionLimited && selectionInsufficient result)
             "selection limited and insufficient"
-        . cover 2 (outputsInsufficient result)
-            "A portion of the minted assets were not spent or burned"
   where
     utxoHasAtLeastOneAsset = not
         . Set.null
@@ -761,11 +757,6 @@ prop_performSelection_small minCoinValueFor costFor (Blind (Small criteria)) =
             . fmap (view #tokens)
             $ outputsToCover criteria
 
-    outputsInsufficient :: PerformSelectionResult -> Bool
-    outputsInsufficient = \case
-        Left (OutputsInsufficient _) -> True
-        _ -> False
-
     selectionLimited :: Bool
     selectionLimited = case view #selectionLimit criteria of
         MaximumInputLimit _ -> True
@@ -962,8 +953,6 @@ prop_performSelection minCoinValueFor costFor (Blind criteria) coverage =
     onFailure = \case
         BalanceInsufficient e ->
             onBalanceInsufficient e
-        OutputsInsufficient e ->
-            onOutputsInsufficient e
         SelectionInsufficient e ->
             onSelectionInsufficient e
         InsufficientMinCoinValues es ->
@@ -1025,27 +1014,6 @@ prop_performSelection minCoinValueFor costFor (Blind criteria) coverage =
         errorBalanceSelected =
             F.foldMap (view #tokens . snd) errorInputsSelected
 
-    onOutputsInsufficient e = do
-        monitor $ counterexample $ unlines
-            [ "assets to mint:"
-            , pretty (Flat errorAssetsToMint)
-            , "assets to burn:"
-            , pretty (Flat errorAssetsToBurn)
-            , "requested output assets:"
-            , pretty (Flat errorRequestedOutputAssets)
-            , "assets minted but not spent or burned:"
-            , pretty (Flat $ missingOutputAssets e)
-            ]
-        assert $ errorAssetsToMint == assetsToMint
-        assert $ errorAssetsToBurn == assetsToBurn
-        assert
-            $ not
-            $ errorAssetsToMint
-                `leq` (errorRequestedOutputAssets <> errorAssetsToBurn)
-      where
-        OutputsInsufficientError
-            errorAssetsToMint errorAssetsToBurn errorRequestedOutputAssets = e
-
     onInsufficientMinCoinValues es = do
         monitor $ counterexample $ unlines
             [ show es