Add SerialiseAsRawBytes instance to UnsignedTx ConwayEra

[palas]

Changelog

- description: |
    Add `SerialiseAsRawBytes` instance to `UnsignedTx ConwayEra`
  type:
  - feature

Context

The standard way of serialising transactions is using CBOR, following the CDDL, and in the case of CIP-30, encoding it as base16. SerialiseAsRawBytes makes this easy. This PR adds SerialiseAsRawBytes instance to UnsignedTx.

Idea comes from this review in a different PR: #852 (comment)

How to trust this PR

It is mainly format changes. Make sure the new instances are implemented correctly and code design is good.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff

[carbolymer]

I agree with @Jimbo4350

[carbolymer]

I think it's better to have those constraints in UnsignedTx. I mean to write:

data UnsignedTx
 = L.EraTx (LedgerEra era) => UnsignedTx (Ledger.Tx (LedgerEra era))

instead of adding them to instances.

Rationale: we'll always be dealing with L.EraTx instances for transactions. Having L.EraTx is easier to understand and satisfy, rather than dealing with more specialised constraints like EncCBOR.

[palas]

Still, that would work for serialiseToRawBytes, but I don't think it is possible to implement deserialiseFromRawBytes without the assumption that era is a valid era

[carbolymer]

But I think we can simplify constraints further:

diff --git c/cardano-api/src/Cardano/Api/Experimental/Tx.hs i/cardano-api/src/Cardano/Api/Experimental/Tx.hs
index 208a65777..1978d1efd 100644
--- c/cardano-api/src/Cardano/Api/Experimental/Tx.hs
+++ i/cardano-api/src/Cardano/Api/Experimental/Tx.hs
@@ -165,7 +165,6 @@ import Cardano.Crypto.Hash qualified as Hash
 import Cardano.Ledger.Alonzo.TxBody qualified as L
 import Cardano.Ledger.Api qualified as L
 import Cardano.Ledger.Binary qualified as Ledger
-import Cardano.Ledger.Conway qualified as Ledger
 import Cardano.Ledger.Conway.TxBody qualified as L
 import Cardano.Ledger.Core qualified as Ledger
 import Cardano.Ledger.Hashes qualified as L hiding (Hash)
@@ -180,8 +179,8 @@ import Lens.Micro
 
 -- | A transaction that can contain everything
 -- except key witnesses.
-newtype UnsignedTx era
-  = UnsignedTx (Ledger.Tx (LedgerEra era))
+data UnsignedTx era
+  = L.EraTx (LedgerEra era) => UnsignedTx (Ledger.Tx (LedgerEra era))
 
 instance HasTypeProxy era => HasTypeProxy (UnsignedTx era) where
   data AsType (UnsignedTx era) = AsUnsignedTx (AsType era)
@@ -189,10 +188,8 @@ instance HasTypeProxy era => HasTypeProxy (UnsignedTx era) where
   proxyToAsType _ = AsUnsignedTx (asType @era)
 
 instance
-  ( L.Era (LedgerEra era)
-  , HasTypeProxy era
-  , Ledger.EncCBOR (Ledger.Tx (LedgerEra era))
-  , Ledger.DecCBOR (Ledger.Annotator (Ledger.Tx (LedgerEra era)))
+  ( HasTypeProxy era
+  , L.EraTx (LedgerEra era)
   )
   => SerialiseAsRawBytes (UnsignedTx era)
   where
@@ -210,9 +207,8 @@ instance
       :: Ledger.DecoderError -> SerialiseAsRawBytesError
     wrapError = SerialiseAsRawBytesError . displayException
 
-instance IsEra era => Show (UnsignedTx era) where
-  showsPrec p (UnsignedTx tx) = case useEra @era of
-    ConwayEra -> showsPrec p (tx :: Ledger.Tx Ledger.ConwayEra)
+instance Show (UnsignedTx era) where
+  showsPrec p (UnsignedTx tx) = showsPrec p tx
 
 newtype UnsignedTxError
   = UnsignedTxError TxBodyError
@@ -366,5 +362,5 @@ convertTxBodyToUnsignedTx sbe txbody =
     (error $ "convertTxBodyToUnsignedTx: Error - unsupported era " <> docToString (pretty sbe))
     ( \w -> do
         let ShelleyTx _ unsignedLedgerTx = makeSignedTransaction [] txbody
-        UnsignedTx $ obtainCommonConstraints w unsignedLedgerTx
+        obtainCommonConstraints w $ UnsignedTx unsignedLedgerTx
     )

[palas]

Huh, so these were not necessary at all:

Ledger.EncCBOR (Ledger.Tx (LedgerEra era))
Ledger.DecCBOR (Ledger.Annotator (Ledger.Tx (LedgerEra era)))

But adding L.EraTx (LedgerEra era) => does simplify the Show instance.

I've applied your patch in: 4bf61df

[Jimbo4350]

LGTM. Squash all the commits before merging.

[carbolymer]

Nice work, thanks!