Merge #17453: gui: Fix intro dialog labels when the prune button is toggled

4f7127d1e3a51f0f55d42a08439c516dcc8d1a26 gui: Make Intro consistent with prune checkbox (Hennadii Stepanov)
4824a7d36cf47e766865e0fefe952ec860eb82dd gui: Add Intro::UpdateFreeSpaceLabel() (Hennadii Stepanov)
daa3f3fa9071a229275dd6a1b8445237ddc3fa97 refactor: Add Intro::UpdatePruneLabels() (Hennadii Stepanov)
e4caa82a03df5c6a6d5d29f34ab006d732c6dac1 refactor: Replace static variable with data member (Hennadii Stepanov)
2bede28cd9ec638d8bb32c187ccf12d89345218e util: Add PruneGBtoMiB() function (Hennadii Stepanov)
e35e4b2ba052c9a533626286026dbe0a2d546c5b util: Add PruneMiBtoGB() function (Hennadii Stepanov)

Pull request description:

  On master (a6f6333ba253cda83221ee529810cacf930e413f) and on 0.19.0.1 the intro dialog with prune enabled (checkbox "Discard blocks..." is checked) provides a user with wrong info about the required disk space:

  ![DeepinScreenshot_bitcoin-qt_20191208112228](https://user-images.githubusercontent.com/32963518/70387510-8daab400-19ae-11ea-9338-29add9c31118.png)

  Also the paragraph "If you have chosen to limit..." is missed.

  ---

  With this PR when prune checkbox is toggled, the related text labels and the amount of required space shown are updated (previously they were only updated when the data directory was updated):
  ![Screenshot from 2019-12-08 11-34-53](https://user-images.githubusercontent.com/32963518/70387542-eed28780-19ae-11ea-9565-49d8a64b2f33.png)

  ---

  This PR is an alternative to #17035.

  **ryanofsky**'s [suggestion](https://github.com/bitcoin/bitcoin/pull/17035#discussion_r337594268) also has been implemented.

ACKs for top commit:
  emilengler:
    ACK 4f7127d1e3a51f0f55d42a08439c516dcc8d1a26
  Sjors:
    tACK 4f7127d1e3a51f0f55d42a08439c516dcc8d1a26
  ryanofsky:
    Code review ACK 4f7127d1e3a51f0f55d42a08439c516dcc8d1a26. It seems like there are a few visible changes here:
  jonasschnelli:
    utACK 4f7127d1e3a51f0f55d42a08439c516dcc8d1a26

Tree-SHA512: fa0bbdcfafde97d7906cda066cbd4608b936a71cae1b4cda3ee3aa2eed3a9795f279f14c6b1b4997278e094db891c7d3bb695368ba0882347aa42165a86e5172

4 files changed, 82 insertions, 48 deletions

diff --git a/src/qt/intro.cpp b/src/qt/intro.cpp
index 53f0c3a108..ad21dfc3ef 100644
--- a/src/qt/intro.cpp
+++ b/src/qt/intro.cpp
@@ -12,6 +12,7 @@
 
 #include <qt/guiconstants.h>
 #include <qt/guiutil.h>
+#include <qt/optionsmodel.h>
 
 #include <interfaces/node.h>
 #include <util/system.h>
@@ -22,9 +23,6 @@
 
 #include <cmath>
 
-/* Total required space (in GB) depending on user choice (prune, not prune) */
-static uint64_t requiredSpace;
-
 /* Check free space asynchronously to prevent hanging the UI thread.
 
    Up to one request to check a path is in flight to this thread; when the check()
@@ -109,14 +107,24 @@ void FreespaceChecker::check()
     Q_EMIT reply(replyStatus, replyMessage, freeBytesAvailable);
 }
 
+namespace {
+//! Return pruning size that will be used if automatic pruning is enabled.
+int GetPruneTargetGB()
+{
+    int64_t prune_target_mib = gArgs.GetArg("-prune", 0);
+    // >1 means automatic pruning is enabled by config, 1 means manual pruning, 0 means no pruning.
+    return prune_target_mib > 1 ? PruneMiBtoGB(prune_target_mib) : DEFAULT_PRUNE_TARGET_GB;
+}
+} // namespace
 
-Intro::Intro(QWidget *parent, uint64_t blockchain_size, uint64_t chain_state_size) :
+Intro::Intro(QWidget *parent, int64_t blockchain_size_gb, int64_t chain_state_size_gb) :
     QDialog(parent),
     ui(new Ui::Intro),
     thread(nullptr),
     signalled(false),
-    m_blockchain_size(blockchain_size),
-    m_chain_state_size(chain_state_size)
+    m_blockchain_size_gb(blockchain_size_gb),
+    m_chain_state_size_gb(chain_state_size_gb),
+    m_prune_target_gb{GetPruneTargetGB()}
 {
     ui->setupUi(this);
     ui->welcomeLabel->setText(ui->welcomeLabel->text().arg(PACKAGE_NAME));
@@ -124,37 +132,24 @@ Intro::Intro(QWidget *parent, uint64_t blockchain_size, uint64_t chain_state_siz
 
     ui->lblExplanation1->setText(ui->lblExplanation1->text()
         .arg(PACKAGE_NAME)
-        .arg(m_blockchain_size)
+        .arg(m_blockchain_size_gb)
         .arg(2009)
         .arg(tr("Bitcoin"))
     );
     ui->lblExplanation2->setText(ui->lblExplanation2->text().arg(PACKAGE_NAME));
 
-    uint64_t pruneTarget = std::max<int64_t>(0, gArgs.GetArg("-prune", 0));
-    if (pruneTarget > 1) { // -prune=1 means enabled, above that it's a size in MB
+    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(pruneTarget ? pruneTarget / 1000 : DEFAULT_PRUNE_TARGET_GB));
-    requiredSpace = m_blockchain_size;
-    QString storageRequiresMsg = tr("At least %1 GB of data will be stored in this directory, and it will grow over time.");
-    if (pruneTarget) {
-        uint64_t prunedGBs = std::ceil(pruneTarget * 1024 * 1024.0 / GB_BYTES);
-        if (prunedGBs <= requiredSpace) {
-            requiredSpace = prunedGBs;
-            storageRequiresMsg = tr("Approximately %1 GB of data will be stored in this directory.");
-        }
-        ui->lblExplanation3->setVisible(true);
-    } else {
-        ui->lblExplanation3->setVisible(false);
-    }
-    requiredSpace += m_chain_state_size;
-    ui->sizeWarningLabel->setText(
-        tr("%1 will download and store a copy of the Bitcoin block chain.").arg(PACKAGE_NAME) + " " +
-        storageRequiresMsg.arg(requiredSpace) + " " +
-        tr("The wallet will also be stored in this directory.")
-    );
-    this->adjustSize();
+    ui->prune->setText(tr("Discard blocks after verification, except most recent %1 GB (prune)").arg(m_prune_target_gb));
+    UpdatePruneLabels(ui->prune->isChecked());
+
+    connect(ui->prune, &QCheckBox::toggled, [this](bool prune_checked) {
+        UpdatePruneLabels(prune_checked);
+        UpdateFreeSpaceLabel();
+    });
+
     startThread();
 }
 
@@ -270,25 +265,31 @@ void Intro::setStatus(int status, const QString &message, quint64 bytesAvailable
     {
         ui->freeSpace->setText("");
     } else {
-        QString freeString = tr("%n GB of free space available", "", bytesAvailable/GB_BYTES);
-        if(bytesAvailable < requiredSpace * GB_BYTES)
-        {
-            freeString += " " + tr("(of %n GB needed)", "", requiredSpace);
-            ui->freeSpace->setStyleSheet("QLabel { color: #800000 }");
-            ui->prune->setChecked(true);
-        } else if (bytesAvailable / GB_BYTES - requiredSpace < 10) {
-            freeString += " " + tr("(%n GB needed for full chain)", "", requiredSpace);
-            ui->freeSpace->setStyleSheet("QLabel { color: #999900 }");
-            ui->prune->setChecked(true);
-        } else {
-            ui->freeSpace->setStyleSheet("");
+        m_bytes_available = bytesAvailable;
+        if (ui->prune->isEnabled()) {
+            ui->prune->setChecked(m_bytes_available < (m_blockchain_size_gb + m_chain_state_size_gb + 10) * GB_BYTES);
         }
-        ui->freeSpace->setText(freeString + ".");
+        UpdateFreeSpaceLabel();
     }
     /* Don't allow confirm in ERROR state */
     ui->buttonBox->button(QDialogButtonBox::Ok)->setEnabled(status != FreespaceChecker::ST_ERROR);
 }
 
+void Intro::UpdateFreeSpaceLabel()
+{
+    QString freeString = tr("%n GB of free space available", "", m_bytes_available / GB_BYTES);
+    if (m_bytes_available < m_required_space_gb * GB_BYTES) {
+        freeString += " " + tr("(of %n GB needed)", "", m_required_space_gb);
+        ui->freeSpace->setStyleSheet("QLabel { color: #800000 }");
+    } else if (m_bytes_available / GB_BYTES - m_required_space_gb < 10) {
+        freeString += " " + tr("(%n GB needed for full chain)", "", m_required_space_gb);
+        ui->freeSpace->setStyleSheet("QLabel { color: #999900 }");
+    } else {
+        ui->freeSpace->setStyleSheet("");
+    }
+    ui->freeSpace->setText(freeString + ".");
+}
+
 void Intro::on_dataDirectory_textChanged(const QString &dataDirStr)
 {
     /* Disable OK button until check result comes in */
@@ -349,3 +350,20 @@ QString Intro::getPathToCheck()
     mutex.unlock();
     return retval;
 }
+
+void Intro::UpdatePruneLabels(bool prune_checked)
+{
+    m_required_space_gb = m_blockchain_size_gb + m_chain_state_size_gb;
+    QString storageRequiresMsg = tr("At least %1 GB of data will be stored in this directory, and it will grow over time.");
+    if (prune_checked && m_prune_target_gb <= m_blockchain_size_gb) {
+        m_required_space_gb = m_prune_target_gb + m_chain_state_size_gb;
+        storageRequiresMsg = tr("Approximately %1 GB of data will be stored in this directory.");
+    }
+    ui->lblExplanation3->setVisible(prune_checked);
+    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) + " " +
+        tr("The wallet will also be stored in this directory.")
+    );
+    this->adjustSize();
+}
diff --git a/src/qt/intro.h b/src/qt/intro.h
index 41da06141f..732393246e 100644
--- a/src/qt/intro.h
+++ b/src/qt/intro.h
@@ -31,7 +31,7 @@ class Intro : public QDialog
 
 public:
     explicit Intro(QWidget *parent = nullptr,
-                   uint64_t blockchain_size = 0, uint64_t chain_state_size = 0);
+                   int64_t blockchain_size_gb = 0, int64_t chain_state_size_gb = 0);
     ~Intro();
 
     QString getDataDirectory();
@@ -67,12 +67,18 @@ private:
     QMutex mutex;
     bool signalled;
     QString pathToCheck;
-    uint64_t m_blockchain_size;
-    uint64_t m_chain_state_size;
+    const int64_t m_blockchain_size_gb;
+    const int64_t m_chain_state_size_gb;
+    //! 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;
 
     void startThread();
     void checkPath(const QString &dataDir);
     QString getPathToCheck();
+    void UpdatePruneLabels(bool prune_checked);
+    void UpdateFreeSpaceLabel();
 
     friend class FreespaceChecker;
 };
diff --git a/src/qt/optionsmodel.cpp b/src/qt/optionsmodel.cpp
index b4b5b32311..977076c4c2 100644
--- a/src/qt/optionsmodel.cpp
+++ b/src/qt/optionsmodel.cpp
@@ -240,9 +240,8 @@ void OptionsModel::SetPruneEnabled(bool prune, bool force)
 {
     QSettings settings;
     settings.setValue("bPrune", prune);
-    // Convert prune size from GB to MiB:
-    const uint64_t nPruneSizeMiB = (settings.value("nPruneSize").toInt() * GB_BYTES) >> 20;
-    std::string prune_val = prune ? std::to_string(nPruneSizeMiB) : "0";
+    const int64_t prune_target_mib = PruneGBtoMiB(settings.value("nPruneSize").toInt());
+    std::string prune_val = prune ? std::to_string(prune_target_mib) : "0";
     if (force) {
         m_node.forceSetArg("-prune", prune_val);
         return;
diff --git a/src/qt/optionsmodel.h b/src/qt/optionsmodel.h
index 524fe268b9..b3260349e7 100644
--- a/src/qt/optionsmodel.h
+++ b/src/qt/optionsmodel.h
@@ -6,6 +6,7 @@
 #define BITCOIN_QT_OPTIONSMODEL_H
 
 #include <amount.h>
+#include <qt/guiconstants.h>
 
 #include <QAbstractListModel>
 
@@ -16,6 +17,16 @@ class Node;
 extern const char *DEFAULT_GUI_PROXY_HOST;
 static constexpr unsigned short DEFAULT_GUI_PROXY_PORT = 9050;
 
+/**
+ * Convert configured prune target MiB to displayed GB. Round up to avoid underestimating max disk usage.
+ */
+static inline int PruneMiBtoGB(int64_t mib) { return (mib * 1024 * 1024 + GB_BYTES - 1) / GB_BYTES; }
+
+/**
+ * Convert displayed prune target GB to configured MiB. Round down so roundtrip GB -> MiB -> GB conversion is stable.
+ */
+static inline int64_t PruneGBtoMiB(int gb) { return gb * GB_BYTES / 1024 / 1024; }
+
 /** Interface from Qt to configuration data structure for Bitcoin client.
    To Qt, the options are presented as a list with the different options
    laid out vertically.