transaction: for witness v0 txins, put both UTXO and WIT_UTXO in psbt

Until now we have been only putting PSBT_IN_NON_WITNESS_UTXO (="UTXO", full tx)
in segwit witness v0 txins, as signers wanted the full tx anyway due to
bip-143 sighash issue [0], and as WITNESS_UTXO can be calculated from UTXO.

My reading of bip-174 is that either behaviour is correct, but
achow101 said bip-174 expects PSBT_IN_WITNESS_UTXO for segwit inputs.
Regardless, including both fields does not increase the tx size too much
(UTXO can be very large ofc but we were already including that, WIT_UTXO is small).
This also might increase compatibility with some other software - I've found
some issues where this might have been the culprit [1][2][3].

closes https://github.com/spesmilo/electrum/issues/8039

related:
[0] https://github.com/spesmilo/electrum/pull/6198
[1] https://github.com/cryptoadvance/specter-desktop/issues/868
[2] https://github.com/cryptoadvance/specter-desktop/issues/1046
[3] https://github.com/cryptoadvance/specter-desktop/issues/1544

electrum/tests/__init__.py

@@ -36,6 +36,8 @@ class SequentialTestCase(unittest.TestCase):
 class ElectrumTestCase(SequentialTestCase):
     """Base class for our unit tests."""
 
+    # maxDiff = None
+
     def setUp(self):
         super().setUp()
         self.asyncio_loop, self._stop_loop, self._loop_thread = util.create_and_start_event_loop()

electrum/transaction.py

@@ -1250,7 +1250,6 @@ class PartialTxInput(TxInput, PSBTSection):
             return
         self._utxo = tx
         self.validate_data()
-        self.ensure_there_is_only_one_utxo()
 
     @property
     def witness_utxo(self):
@@ -1260,7 +1259,6 @@ class PartialTxInput(TxInput, PSBTSection):
     def witness_utxo(self, value: Optional[TxOutput]):
         self._witness_utxo = value
         self.validate_data()
-        self.ensure_there_is_only_one_utxo()
 
     def to_json(self):
         d = super().to_json()
@@ -1387,7 +1385,6 @@ class PartialTxInput(TxInput, PSBTSection):
             self._unknown[full_key] = val
 
     def serialize_psbt_section_kvs(self, wr):
-        self.ensure_there_is_only_one_utxo()
         if self.witness_utxo:
             wr(PSBTInputType.WITNESS_UTXO, self.witness_utxo.serialize_to_network())
         if self.utxo:
@@ -1515,16 +1512,10 @@ class PartialTxInput(TxInput, PSBTSection):
             if other_txin.witness_script is not None:
                 self.witness_script = other_txin.witness_script
             self._unknown.update(other_txin._unknown)
-        self.ensure_there_is_only_one_utxo()
+        self.validate_data()
         # try to finalize now
         self.finalize()
 
-    def ensure_there_is_only_one_utxo(self):
-        # we prefer having the full previous tx, even for segwit inputs. see #6198
-        # for witness v1, witness_utxo will be enough though
-        if self.utxo is not None and self.witness_utxo is not None:
-            self.witness_utxo = None
-
     def convert_utxo_to_witness_utxo(self) -> None:
         if self.utxo:
             self._witness_utxo = self.utxo.outputs()[self.prevout.out_idx]

electrum/wallet.py

@@ -2130,9 +2130,12 @@ class Abstract_Wallet(ABC, Logger, EventListener):
             address: str = None,
             ignore_network_issues: bool = True,
     ) -> None:
-        # We prefer to include UTXO (full tx) for every input.
-        # We cannot include UTXO if the prev tx is not signed yet though (chain of unsigned txs),
-        # in which case we might include a WITNESS_UTXO.
+        # - We prefer to include UTXO (full tx), even for segwit inputs (see #6198).
+        # - For witness v0 inputs, we include *both* UTXO and WITNESS_UTXO. UTXO is a strict superset,
+        #   so this is redundant, but it is (implied to be) "expected" from bip-0174 (see #8039).
+        #   Regardless, this might improve compatibility with some other software.
+        # - For witness v1, witness_utxo will be enough though (bip-0341 sighash fixes known prior issues).
+        # - We cannot include UTXO if the prev tx is not signed yet (chain of unsigned txs).
         address = address or txin.address
         if txin.witness_utxo is None and txin.is_segwit() and address:
             received, spent = self.adb.get_addr_io(address)
@@ -2142,7 +2145,6 @@ class Abstract_Wallet(ABC, Logger, EventListener):
                 txin.witness_utxo = TxOutput.from_address_and_value(address, txin_value)
         if txin.utxo is None:
             txin.utxo = self.get_input_tx(txin.prevout.txid.hex(), ignore_network_issues=ignore_network_issues)
-        txin.ensure_there_is_only_one_utxo()
 
     def _learn_derivation_path_for_address_from_txinout(self, txinout: Union[PartialTxInput, PartialTxOutput],
                                                         address: str) -> bool: