Merge #17492: QT: bump fee returns PSBT on clipboard for watchonly-only wallets

3c30d71 QT: Change bumpFee asserts to simple error message (Gregory Sanders)
e3b19d8 QT: bump fee returns PSBT on clipboard for watchonly-only wallets (Gregory Sanders)

Pull request description:

  Very small set of changes to support PSBT-based fee bumping on watchonly wallets in QT.

  quasi-companion to bitcoin/bitcoin#16373

ACKs for top commit:
  gwillen:
    code review ACK 3c30d71
  promag:
    Code review ACK 3c30d71.
  Sjors:
    utACK 3c30d71
  achow101:
    ACK 3c30d71

Tree-SHA512: 7a706141e46d7fd0ad513a08a96c16f2e7e531427a6776b689362f82e32cbd9d4b7eeb98f6936aa3f9347d23ccc94128516fcffa695efacd9cac43606ea916e2

Author: fanquake

src/qt/walletmodel.cpp

@@ -10,6 +10,7 @@
 
 #include <qt/addresstablemodel.h>
 #include <qt/guiconstants.h>
+#include <qt/guiutil.h>
 #include <qt/optionsmodel.h>
 #include <qt/paymentserver.h>
 #include <qt/recentrequeststablemodel.h>
@@ -487,8 +488,10 @@ bool WalletModel::bumpFee(uint256 hash, uint256& new_hash)
          return false;
     }
 
+    const bool create_psbt = privateKeysDisabled();
+
     // allow a user based fee verification
-    QString questionString = tr("Do you want to increase the fee?");
+    QString questionString = create_psbt ? tr("Do you want to draft a transaction with fee increase?") : tr("Do you want to increase the fee?");
     questionString.append("<br />");
     questionString.append("<table style=\"text-align: left;\">");
     questionString.append("<tr><td>");
@@ -519,6 +522,23 @@ bool WalletModel::bumpFee(uint256 hash, uint256& new_hash)
         return false;
     }
 
+    // Short-circuit if we are returning a bumped transaction PSBT to clipboard
+    if (create_psbt) {
+        PartiallySignedTransaction psbtx(mtx);
+        bool complete = false;
+        const TransactionError err = wallet().fillPSBT(psbtx, complete, SIGHASH_ALL, false /* sign */, true /* bip32derivs */);
+        if (err != TransactionError::OK || complete) {
+            QMessageBox::critical(nullptr, tr("Fee bump error"), tr("Can't draft transaction."));
+            return false;
+        }
+        // Serialize the PSBT
+        CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
+        ssTx << psbtx;
+        GUIUtil::setClipboard(EncodeBase64(ssTx.str()).c_str());
+        Q_EMIT message(tr("PSBT copied"), "Copied to clipboard", CClientUIInterface::MSG_INFORMATION);
+        return true;
+    }
+
     // sign bumped transaction
     if (!m_wallet->signBumpTransaction(mtx)) {
         QMessageBox::critical(nullptr, tr("Fee bump error"), tr("Can't sign transaction."));