Replace unsafe function coinQuantity.

This function is unsafe because `Coin` is now defined in terms of `Natural`.

We replace this function with a pair of functions:

- Coin.toQuantity        :: Integral i => Coin -> Maybe (Quantity n i)
- Coin.unsafeToQuantity  :: Integral i => Coin ->        Quantity n i

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

@@ -420,7 +420,7 @@ import Cardano.Wallet.Primitive.Types
 import Cardano.Wallet.Primitive.Types.Address
     ( Address (..), AddressState (..) )
 import Cardano.Wallet.Primitive.Types.Coin
-    ( Coin (..), coinQuantity )
+    ( Coin (..) )
 import Cardano.Wallet.Primitive.Types.Hash
     ( Hash (..) )
 import Cardano.Wallet.Primitive.Types.Redeemer
@@ -596,6 +596,7 @@ import qualified Cardano.Wallet.Primitive.AddressDerivation.Icarus as Icarus
 import qualified Cardano.Wallet.Primitive.CoinSelection.Balance as Balance
 import qualified Cardano.Wallet.Primitive.CoinSelection.Collateral as Collateral
 import qualified Cardano.Wallet.Primitive.Types as W
+import qualified Cardano.Wallet.Primitive.Types.Coin as Coin
 import qualified Cardano.Wallet.Primitive.Types.TokenBundle as TokenBundle
 import qualified Cardano.Wallet.Primitive.Types.TokenMap as TokenMap
 import qualified Cardano.Wallet.Primitive.Types.Tx as W
@@ -3241,8 +3242,8 @@ mkApiFee :: Maybe Coin -> [Coin] -> FeeEstimation -> ApiFee
 mkApiFee mDeposit minCoins (FeeEstimation estMin estMax) = ApiFee
     { estimatedMin = qty estMin
     , estimatedMax = qty estMax
-    , minimumCoins = coinQuantity <$> minCoins
-    , deposit = coinQuantity $ fromMaybe (Coin 0) mDeposit
+    , minimumCoins = Coin.unsafeToQuantity <$> minCoins
+    , deposit = Coin.unsafeToQuantity $ fromMaybe (Coin 0) mDeposit
     }
   where
     qty = Quantity . fromIntegral

lib/core/src/Cardano/Wallet/Primitive/Types/Coin.hs

@@ -18,14 +18,15 @@ module Cardano.Wallet.Primitive.Types.Coin
       -- * Conversions (Safe)
     , fromIntegral
     , fromWord64
+    , toQuantity
     , toWord64
 
       -- * Conversions (Unsafe)
     , unsafeFromIntegral
+    , unsafeToQuantity
     , unsafeToWord64
 
       -- * Compatibility
-    , coinQuantity
     , coinToInteger
     , coinToNatural
     , unsafeNaturalToCoin
@@ -143,6 +144,14 @@ fromIntegral i = Coin <$> intCastMaybe i
 fromWord64 :: Word64 -> Coin
 fromWord64 = Coin . intCast
 
+-- | Converts a 'Coin' to a 'Quantity'.
+--
+-- Returns 'Nothing' if the given value does not fit within the bounds of
+-- the target type.
+--
+toQuantity :: (Bits i, Integral i) => Coin -> Maybe (Quantity n i)
+toQuantity (Coin c) = Quantity <$> intCastMaybe c
+
 -- | Converts a 'Coin' to a 'Word64' value.
 --
 -- Returns 'Nothing' if the given value does not fit within the bounds of a
@@ -175,6 +184,26 @@ unsafeFromIntegral i = fromMaybe onError (fromIntegral i)
         , "is not a natural number."
         ]
 
+-- | Converts a 'Coin' to a 'Quantity'.
+--
+-- Callers of this function must take responsibility for checking that the
+-- given value will fit within the bounds of the target type.
+--
+-- Produces a run-time error if the given value is out of bounds.
+--
+unsafeToQuantity
+    :: HasCallStack
+    => (Bits i, Integral i)
+    => Coin
+    -> Quantity n i
+unsafeToQuantity c = fromMaybe onError (toQuantity c)
+  where
+    onError = error $ unwords
+        [ "Coin.unsafeToQuantity:"
+        , show c
+        , "does not fit within the bounds of the target type."
+        ]
+
 -- | Converts a 'Coin' to a 'Word64' value.
 --
 -- Callers of this function must take responsibility for checking that the
@@ -195,11 +224,6 @@ unsafeToWord64 c = fromMaybe onError (toWord64 c)
                                Compatibility
 -------------------------------------------------------------------------------}
 
--- | Compatibility function to use while 'Quantity' is still used in non-API
--- parts of the code.
-coinQuantity :: Integral a => Coin -> Quantity n a
-coinQuantity (Coin n) = Quantity (Prelude.fromIntegral n)
-
 coinToInteger :: Coin -> Integer
 coinToInteger = Prelude.fromIntegral . unCoin