Merge bitcoin-core/gui#390: Add SubFeeFromAmount to options

62b125fd197879f112322a1f67a318d6ab22e67a qt, refactor: Fix indentation (Prateek Sancheti)
ad28b66e98c9bb3bc7af2545654842544a798601 qt: Add SubFeeFromAmount option (Prateek Sancheti)

Pull request description:

  This PR adds **_SubFeeFromAmount_** option which lets the user select their preferred setting of whether fee for a transaction is to be subtracted from the amount or not for future transactions. The setting chosen by the user is remembered even when the GUI mode is turned off.

  **_Functionality and Usage:_**

  - Go to `Settings > Options > Wallet` on _Windows/Linux_ or `bitcoin-qt > Preferences > Wallet` on _macOS_.
  - The checkbox **Subtract Fee From Amount** corresponds to the added option **SubFeeFromAmount**.
  - The preferred setting intended to be the default for all future send transactions should be selected by the user.
  - Click on **OK**.
  - Go to the **Send** tab in the wallet.
  - You shall notice, any new Send transaction created will have the preferred setting as chosen by the user.<br> (Try clicking on Add recipient or even restarting the Node in GUI)

  Attaching ScreenRecordings to explain the added feature.

  > Master.mov: Master Branch

  https://user-images.githubusercontent.com/54016434/127763378-be91837d-d0ab-4ae5-87c0-d303fa70a336.mov

  > PR.mov: PullRequest

  https://user-images.githubusercontent.com/54016434/127763404-05b834c1-4082-4fbd-9b05-1528ac898a21.mov

  Close #386

ACKs for top commit:
  Talkless:
    tACK 62b125fd197879f112322a1f67a318d6ab22e67a, tested on Debian Sid with 5.15.2 and it works as described.
  hebasto:
    re-ACK 62b125fd197879f112322a1f67a318d6ab22e67a, only removed the unused `SubFeeFromAmountChanged` signal since my [previous](https://github.com/bitcoin-core/gui/pull/390#pullrequestreview-726531766) review.
  meshcollider:
    utACK 62b125fd197879f112322a1f67a318d6ab22e67a

Tree-SHA512: 932ca89ae578a1e1c426561400d87cf005c231944feaf0f662ff8d88f32bdd65a927a090ea41510a15f8ec0ebcd5529672e9917720eb5ea85f413f081e45d5bb

src/qt/forms/optionsdialog.ui

@@ -315,6 +315,16 @@
      </widget>
      <widget class="QWidget" name="pageWallet">
       <layout class="QVBoxLayout" name="verticalLayout_Wallet">
+       <item>
+        <widget class="QCheckBox" name="subFeeFromAmount">
+         <property name="toolTip">
+          <string extracomment="Tooltip text for Options window setting that sets subtracting the fee from a sending amount as default.">Whether to set subtract fee from amount as default or not.</string>
+         </property>
+         <property name="text">
+          <string extracomment="An Options window setting to set subtracting the fee from a sending amount as default.">Subtract &amp;fee from amount by default</string>
+         </property>
+        </widget>
+       </item>
        <item>
         <layout class="QVBoxLayout" name="verticalLayout_2">
          <item>

src/qt/optionsdialog.cpp

@@ -325,6 +325,7 @@ void OptionsDialog::setMapper()
 
     /* Wallet */
     mapper->addMapping(ui->coinControlFeatures, OptionsModel::CoinControlFeatures);
+    mapper->addMapping(ui->subFeeFromAmount, OptionsModel::SubFeeFromAmount);
     mapper->addMapping(ui->keepChangeAddress, OptionsModel::KeepChangeAddress);
     mapper->addMapping(ui->showMasternodesTab, OptionsModel::ShowMasternodesTab);
     mapper->addMapping(ui->showGovernanceTab, OptionsModel::ShowGovernanceTab);

src/qt/optionsmodel.cpp

@@ -222,6 +222,11 @@ void OptionsModel::Init(bool resetSettings)
     if (!gArgs.SoftSetBoolArg("-spendzeroconfchange", settings.value("bSpendZeroConfChange").toBool()))
         addOverriddenOption("-spendzeroconfchange");
 
+    if (!settings.contains("SubFeeFromAmount")) {
+        settings.setValue("SubFeeFromAmount", false);
+    }
+    m_sub_fee_from_amount = settings.value("SubFeeFromAmount", false).toBool();
+
     // CoinJoin
     if (!settings.contains("nCoinJoinSessions"))
         settings.setValue("nCoinJoinSessions", DEFAULT_COINJOIN_SESSIONS);
@@ -458,6 +463,8 @@ QVariant OptionsModel::data(const QModelIndex & index, int role) const
 #ifdef ENABLE_WALLET
         case SpendZeroConfChange:
             return settings.value("bSpendZeroConfChange");
+        case SubFeeFromAmount:
+            return m_sub_fee_from_amount;
         case ShowMasternodesTab:
             return settings.value("fShowMasternodesTab");
         case ShowGovernanceTab:
@@ -633,6 +640,10 @@ bool OptionsModel::setData(const QModelIndex & index, const QVariant & value, in
                 setRestartRequired(true);
             }
             break;
+        case SubFeeFromAmount:
+            m_sub_fee_from_amount = value.toBool();
+            settings.setValue("SubFeeFromAmount", m_sub_fee_from_amount);
+            break;
         case ShowGovernanceTab:
             if (settings.value("fShowGovernanceTab") != value) {
                 settings.setValue("fShowGovernanceTab", value);

src/qt/optionsmodel.h

@@ -67,6 +67,7 @@ public:
         FontWeightBold,       // int
         Language,             // QString
         CoinControlFeatures,  // bool
+        SubFeeFromAmount,     // bool
         KeepChangeAddress,    // bool
         ThreadsScriptVerif,   // int
         Prune,                // bool
@@ -105,6 +106,7 @@ public:
     int getDisplayUnit() const { return nDisplayUnit; }
     QString getThirdPartyTxUrls() const { return strThirdPartyTxUrls; }
     bool getCoinControlFeatures() const { return fCoinControlFeatures; }
+    bool getSubFeeFromAmount() const { return m_sub_fee_from_amount; }
     bool getKeepChangeAddress() const { return fKeepChangeAddress; }
     bool getShowAdvancedCJUI() { return fShowAdvancedCJUI; }
     const QString& getOverriddenByCommandLine() { return strOverriddenByCommandLine; }
@@ -132,6 +134,7 @@ private:
     int nDisplayUnit;
     QString strThirdPartyTxUrls;
     bool fCoinControlFeatures;
+    bool m_sub_fee_from_amount;
     bool fKeepChangeAddress;
     bool fShowAdvancedCJUI;
     /* settings that were overridden by command-line */

src/qt/sendcoinsentry.cpp

@@ -103,7 +103,9 @@ void SendCoinsEntry::clear()
     ui->payTo->clear();
     ui->addAsLabel->clear();
     ui->payAmount->clear();
-    ui->checkboxSubtractFeeFromAmount->setCheckState(Qt::Unchecked);
+    if (model && model->getOptionsModel()) {
+        ui->checkboxSubtractFeeFromAmount->setChecked(model->getOptionsModel()->getSubFeeFromAmount());
+    }
     ui->messageTextLabel->clear();
     ui->messageTextLabel->hide();
     ui->messageLabel->hide();