Merge bitcoin-core/gui#125: Enable changing the autoprune block space size in intro dialog

415fb2e1abac189fcbe8eccf2ea065724d17460f GUI/Intro: Move prune setting below explanation (Luke Dashjr)
2a84c6bcf61429ac507b506a39247b3a66edbcb4 GUI/Intro: Estimate max age of backups that can be restored with pruning (Luke Dashjr)
e2dcd957fa206a28404ff824fb764b8889705fb2 GUI/Intro: Rework UI flow to let the user set prune size in GBs (Luke Dashjr)
f2e5a6b54fa38b10d822609939b8108bd8fe041b GUI/Intro: Abstract GUI-to-option into Intro::getPrune (Luke Dashjr)
62932cc686dc46ce14c026993deea8e561654177 GUI/Intro: Return actual prune setting from showIfNeeded (Luke Dashjr)

Pull request description:

  ![Screenshot_20200911_095102](https://user-images.githubusercontent.com/1095675/92933661-0c4cea00-f436-11ea-9853-2456091ffab3.png)

  Moved from https://github.com/bitcoin/bitcoin/pull/18728

ACKs for top commit:
  ryanofsky:
    Code review ACK 415fb2e1abac189fcbe8eccf2ea065724d17460f. Changes since last review: mb/gib suffixes, constexpr QOverload expected_backup_days tweaks, new moveonly layout commit
  jarolrod:
    Tested ACK 415fb2e.
  Talkless:
    tACK 415fb2e1abac189fcbe8eccf2ea065724d17460f, tested on Debian Sid with Qt 5.15.2.
  hebasto:
    ACK 415fb2e1abac189fcbe8eccf2ea065724d17460f, my unresolved comments are not blockers, and they could be resolved in follow ups.

Tree-SHA512: bd4882a9c08e6a6eb14b7fb6366983db8581425b4949fea212785d34d8fad9e32fb81ca8c8cdbfb2c05ea394aaf5a746ba2cf16623795c7252c3bdb61d455f00

5 files changed, 79 insertions, 24 deletions

diff --git a/src/qt/bitcoin.cpp b/src/qt/bitcoin.cpp
index de71b7dea7..a30cac3504 100644
--- a/src/qt/bitcoin.cpp
+++ b/src/qt/bitcoin.cpp
@@ -319,11 +319,9 @@ void BitcoinApplication::parameterSetup()
     InitParameterInteraction(gArgs);
 }
 
-void BitcoinApplication::InitializePruneSetting(bool prune)
+void BitcoinApplication::InitPruneSetting(int64_t prune_MiB)
 {
-    // If prune is set, intentionally override existing prune size with
-    // the default size since this is called when choosing a new datadir.
-    optionsModel->SetPruneTargetGB(prune ? DEFAULT_PRUNE_TARGET_GB : 0, true);
+    optionsModel->SetPruneTargetGB(PruneMiBtoGB(prune_MiB), true);
 }
 
 void BitcoinApplication::requestInitialize()
@@ -533,9 +531,9 @@ int GuiMain(int argc, char* argv[])
     /// 5. Now that settings and translations are available, ask user for data directory
     // User language is set up: pick a data directory
     bool did_show_intro = false;
-    bool prune = false; // Intro dialog prune check box
+    int64_t prune_MiB = 0;  // Intro dialog prune configuration
     // Gracefully exit if the user cancels
-    if (!Intro::showIfNeeded(did_show_intro, prune)) return EXIT_SUCCESS;
+    if (!Intro::showIfNeeded(did_show_intro, prune_MiB)) return EXIT_SUCCESS;
 
     /// 6. Determine availability of data directory and parse bitcoin.conf
     /// - Do not call GetDataDir(true) before this step finishes
@@ -617,7 +615,7 @@ int GuiMain(int argc, char* argv[])
 
     if (did_show_intro) {
         // Store intro dialog settings other than datadir (network specific)
-        app.InitializePruneSetting(prune);
+        app.InitPruneSetting(prune_MiB);
     }
 
     if (gArgs.GetBoolArg("-splash", DEFAULT_SPLASHSCREEN) && !gArgs.GetBoolArg("-min", false))
diff --git a/src/qt/bitcoin.h b/src/qt/bitcoin.h
index 5fd6bd607f..f9fab0534b 100644
--- a/src/qt/bitcoin.h
+++ b/src/qt/bitcoin.h
@@ -68,7 +68,7 @@ public:
     /// Create options model
     void createOptionsModel(bool resetSettings);
     /// Initialize prune setting
-    void InitializePruneSetting(bool prune);
+    void InitPruneSetting(int64_t prune_MiB);
     /// Create main window
     void createWindow(const NetworkStyle *networkStyle);
     /// Create splash screen
diff --git a/src/qt/forms/intro.ui b/src/qt/forms/intro.ui
index f27a4ebe44..a1e94f99e6 100644
--- a/src/qt/forms/intro.ui
+++ b/src/qt/forms/intro.ui
@@ -7,7 +7,7 @@
     <x>0</x>
     <y>0</y>
     <width>674</width>
-    <height>415</height>
+    <height>447</height>
    </rect>
   </property>
   <property name="windowTitle">
@@ -211,16 +211,6 @@
     </widget>
    </item>
    <item>
-    <widget class="QCheckBox" name="prune">
-     <property name="toolTip">
-      <string>Reverting this setting requires re-downloading the entire blockchain. It is faster to download the full chain first and prune it later. Disables some advanced features.</string>
-     </property>
-     <property name="text">
-      <string></string>
-     </property>
-    </widget>
-   </item>
-   <item>
     <widget class="QLabel" name="lblExplanation2">
      <property name="text">
       <string>This initial synchronisation is very demanding, and may expose hardware problems with your computer that had previously gone unnoticed. Each time you run %1, it will continue downloading where it left off.</string>
@@ -241,6 +231,47 @@
     </widget>
    </item>
    <item>
+    <layout class="QHBoxLayout" name="pruneOptLayout">
+     <item>
+      <widget class="QCheckBox" name="prune">
+       <property name="text">
+        <string>Limit block chain storage to</string>
+       </property>
+       <property name="toolTip">
+        <string>Reverting this setting requires re-downloading the entire blockchain. It is faster to download the full chain first and prune it later. Disables some advanced features.</string>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <widget class="QSpinBox" name="pruneGB">
+       <property name="suffix">
+        <string> GB</string>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <widget class="QLabel" name="lblPruneSuffix">
+       <property name="buddy">
+        <cstring>pruneGB</cstring>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <spacer name="horizontalSpacer_2">
+       <property name="orientation">
+        <enum>Qt::Horizontal</enum>
+       </property>
+       <property name="sizeHint" stdset="0">
+        <size>
+         <width>40</width>
+         <height>20</height>
+        </size>
+       </property>
+      </spacer>
+     </item>
+    </layout>
+   </item>
+   <item>
     <spacer name="verticalSpacer">
      <property name="orientation">
       <enum>Qt::Vertical</enum>
diff --git a/src/qt/intro.cpp b/src/qt/intro.cpp
index aa6b2665fa..ed39307fd7 100644
--- a/src/qt/intro.cpp
+++ b/src/qt/intro.cpp
@@ -17,6 +17,7 @@
 
 #include <interfaces/node.h>
 #include <util/system.h>
+#include <validation.h>
 
 #include <QFileDialog>
 #include <QSettings>
@@ -139,17 +140,26 @@ Intro::Intro(QWidget *parent, int64_t blockchain_size_gb, int64_t chain_state_si
     );
     ui->lblExplanation2->setText(ui->lblExplanation2->text().arg(PACKAGE_NAME));
 
+    const int min_prune_target_GB = std::ceil(MIN_DISK_SPACE_FOR_BLOCK_FILES / 1e9);
+    ui->pruneGB->setRange(min_prune_target_GB, std::numeric_limits<int>::max());
     if (gArgs.GetArg("-prune", 0) > 1) { // -prune=1 means enabled, above that it's a size in MiB
         ui->prune->setChecked(true);
         ui->prune->setEnabled(false);
     }
-    ui->prune->setText(tr("Discard blocks after verification, except most recent %1 GB (prune)").arg(m_prune_target_gb));
+    ui->pruneGB->setValue(m_prune_target_gb);
+    ui->pruneGB->setToolTip(ui->prune->toolTip());
+    ui->lblPruneSuffix->setToolTip(ui->prune->toolTip());
     UpdatePruneLabels(ui->prune->isChecked());
 
     connect(ui->prune, &QCheckBox::toggled, [this](bool prune_checked) {
         UpdatePruneLabels(prune_checked);
         UpdateFreeSpaceLabel();
     });
+    connect(ui->pruneGB, QOverload<int>::of(&QSpinBox::valueChanged), [this](int prune_GB) {
+        m_prune_target_gb = prune_GB;
+        UpdatePruneLabels(ui->prune->isChecked());
+        UpdateFreeSpaceLabel();
+    });
 
     startThread();
 }
@@ -182,7 +192,17 @@ void Intro::setDataDirectory(const QString &dataDir)
     }
 }
 
-bool Intro::showIfNeeded(bool& did_show_intro, bool& prune)
+int64_t Intro::getPruneMiB() const
+{
+    switch (ui->prune->checkState()) {
+    case Qt::Checked:
+        return PruneGBtoMiB(m_prune_target_gb);
+    case Qt::Unchecked: default:
+        return 0;
+    }
+}
+
+bool Intro::showIfNeeded(bool& did_show_intro, int64_t& prune_MiB)
 {
     did_show_intro = false;
 
@@ -233,7 +253,7 @@ bool Intro::showIfNeeded(bool& did_show_intro, bool& prune)
         }
 
         // Additional preferences:
-        prune = intro.ui->prune->isChecked();
+        prune_MiB = intro.getPruneMiB();
 
         settings.setValue("strDataDir", dataDir);
         settings.setValue("fReset", false);
@@ -361,6 +381,11 @@ void Intro::UpdatePruneLabels(bool prune_checked)
         storageRequiresMsg = tr("Approximately %1 GB of data will be stored in this directory.");
     }
     ui->lblExplanation3->setVisible(prune_checked);
+    ui->pruneGB->setEnabled(prune_checked);
+    static constexpr uint64_t nPowTargetSpacing = 10 * 60;  // from chainparams, which we don't have at this stage
+    static constexpr uint32_t expected_block_data_size = 2250000;  // includes undo data
+    const uint64_t expected_backup_days = m_prune_target_gb * 1e9 / (uint64_t(expected_block_data_size) * 86400 / nPowTargetSpacing);
+    ui->lblPruneSuffix->setText(tr("(sufficient to restore backups %n day(s) old)", "block chain pruning", expected_backup_days));
     ui->sizeWarningLabel->setText(
         tr("%1 will download and store a copy of the Bitcoin block chain.").arg(PACKAGE_NAME) + " " +
         storageRequiresMsg.arg(m_required_space_gb) + " " +
diff --git a/src/qt/intro.h b/src/qt/intro.h
index 51f42de7ac..88fe2b722d 100644
--- a/src/qt/intro.h
+++ b/src/qt/intro.h
@@ -36,6 +36,7 @@ public:
 
     QString getDataDirectory();
     void setDataDirectory(const QString &dataDir);
+    int64_t getPruneMiB() const;
 
     /**
      * Determine data directory. Let the user choose if the current one doesn't exist.
@@ -47,7 +48,7 @@ public:
      * @note do NOT call global GetDataDir() before calling this function, this
      * will cause the wrong path to be cached.
      */
-    static bool showIfNeeded(bool& did_show_intro, bool& prune);
+    static bool showIfNeeded(bool& did_show_intro, int64_t& prune_MiB);
 
 Q_SIGNALS:
     void requestCheck();
@@ -72,7 +73,7 @@ private:
     //! Total required space (in GB) depending on user choice (prune or not prune).
     int64_t m_required_space_gb{0};
     uint64_t m_bytes_available{0};
-    const int64_t m_prune_target_gb;
+    int64_t m_prune_target_gb;
 
     void startThread();
     void checkPath(const QString &dataDir);