fixes for txin.make_witness:

- add witness_sizehint
  - fix make_unsigned_transaction
  - do not remove witness_script in tx.finalize()

electrum/transaction.py

@@ -913,6 +913,10 @@ class Transaction:
         if not txin.is_segwit():
             return construct_witness([])
 
+        if estimate_size and hasattr(txin, 'make_witness'):
+            sig_dummy = b'\x00' * 71  # DER-encoded ECDSA sig, with low S and low R
+            txin.witness_sizehint = len(txin.make_witness(sig_dummy))
+
         if estimate_size and txin.witness_sizehint is not None:
             return bytes(txin.witness_sizehint)
 
@@ -1739,7 +1743,8 @@ class PartialTxInput(TxInput, PSBTSection):
             self.sighash = None
             self.bip32_paths = {}
             self.redeem_script = None
-            self.witness_script = None
+            # FIXME: side effect interfers with make_witness
+            # self.witness_script = None
 
         if self.script_sig is not None and self.witness is not None:
             clear_fields_when_finalized()

electrum/wallet.py

@@ -1876,8 +1876,13 @@ class Abstract_Wallet(ABC, Logger, EventListener):
                 # make sure we don't try to spend change from the tx-to-be-replaced:
                 coins = [c for c in coins if c.prevout.txid.hex() != base_tx.txid()]
                 is_local = self.adb.get_tx_height(base_tx.txid()).height == TX_HEIGHT_LOCAL
-                base_tx = PartialTransaction.from_tx(base_tx)
-                base_tx.add_info_from_wallet(self)
+                if not isinstance(base_tx, PartialTransaction):
+                    base_tx = PartialTransaction.from_tx(base_tx)
+                    base_tx.add_info_from_wallet(self)
+                else:
+                    # don't cast PartialTransaction, because it removes make_witness
+                    for txin in base_tx.inputs():
+                        txin.witness = None
                 base_tx_fee = base_tx.get_fee()
                 base_feerate = Decimal(base_tx_fee)/base_tx.estimated_size()
                 relayfeerate = Decimal(self.relayfee()) / 1000