Merge bitcoin-core#186: Add information to "Confirm fee bump" window

232d1f9 Add information to "Confirm fee bump" window (Prayank)

Pull request description:

  + Add information in bump fee confirmation box according to the documentation: https://bitcoincore.org/en/doc/0.20.0/rpc/wallet/bumpfee/

  + Workaround to fix issue: bitcoin/bitcoin#20795 in which user isn't aware of new inputs, outputs added to replacement transaction before broadcasting. Initial transaction had used coin control features and custom change address. Until the issue is fixed by change in coin selection algorithm we can add this warning.

  + Waiting for comments from devs who are working on coin selection algorithm PRs or involved in related research. However got two comments from Luke Dashjr and Pieter Wuille:

  _luke-jr: Reducing the change output also could be a privacy problem, since it identifies which output was change._

  _sipa: Wallet doesn't know the original transaction was using coin control. So I think its expected that if you use automatic fee bumping, you'll get whatever the coin selection algorithm decides. As for why its not decreasing the change and instead adding another input, that may be a bug._  (IRC: #bitcoin-core-dev)

ACKs for top commit:
  jonasschnelli:
    Tested ACK - 232d1f9

Tree-SHA512: 2ff65db1ddb1d4a45f82670b6ca303a0bf48acf3d09defffc21f44ec81cb6182268959706f592f3442aae5db48f43b8ea86973d74ec2721be93d209ce0414953

Author: jonasschnelli

src/qt/walletmodel.cpp

@@ -514,6 +514,13 @@ bool WalletModel::bumpFee(uint256 hash, uint256& new_hash)
     questionString.append("</td><td>");
     questionString.append(BitcoinUnits::formatHtmlWithUnit(getOptionsModel()->getDisplayUnit(), new_fee));
     questionString.append("</td></tr></table>");
+
+    // Display warning in the "Confirm fee bump" window if the "Coin Control Features" option is enabled
+    if (getOptionsModel()->getCoinControlFeatures()) {
+        questionString.append("<br><br>");
+        questionString.append(tr("Warning: This may pay the additional fee by reducing change outputs or adding inputs, when necessary. It may add a new change output if one does not already exist. These changes may potentially leak privacy."));
+    }
+
     SendConfirmationDialog confirmationDialog(tr("Confirm fee bump"), questionString);
     confirmationDialog.exec();
     QMessageBox::StandardButton retval = static_cast<QMessageBox::StandardButton>(confirmationDialog.result());