Merge bitcoin#19210: qt: Get rid of cursor in out-of-focus labels

bd315eb qt: Get rid of cursor in out-of-focus labels (Hennadii Stepanov)

Pull request description:

  After clicking on `QLabel` with selectable text the cursor remains forever:

  ![47532924-65e7b200-d8ba-11e8-9254-7bde658961cb](https://user-images.githubusercontent.com/32963518/84038485-ad945200-a9a8-11ea-89e3-c7c17d02a611.png)

  This PR fixes this visual bug.

  Earlier attempts to fix this issue:
  - bitcoin#14577
  - bitcoin#14810 (combined with other UX feature)

ACKs for top commit:
  promag:
    Code review ACK bd315eb.
  laanwj:
    Tested ACK bd315eb

Tree-SHA512: 6bf89362412e5ce9a4dec6944b62fe44fc31ca49cda7f6e2eb37e847fac9dccb68bca7ac6877b19e42add2333e40d0b4265757ead105ac0a5d28f8ab43b322c3

Author: laanwj

src/qt/bitcoin.cpp

@@ -556,6 +556,8 @@ int GuiMain(int argc, char* argv[])
     /// 9. Main GUI initialization
     // Install global event filter that makes sure that long tooltips can be word-wrapped
     app.installEventFilter(new GUIUtil::ToolTipToRichTextFilter(TOOLTIP_WRAP_THRESHOLD, &app));
+    // Install global event filter that makes sure that out-of-focus labels do not contain text cursor.
+    app.installEventFilter(new GUIUtil::LabelOutOfFocusEventFilter(&app));
 #if defined(Q_OS_WIN)
     // Install global event filter for processing Windows session related Windows messages (WM_QUERYENDSESSION and WM_ENDSESSION)
     qApp->installNativeEventFilter(new WinShutdownMonitor());

src/qt/guiutil.cpp

@@ -450,6 +450,28 @@ bool ToolTipToRichTextFilter::eventFilter(QObject *obj, QEvent *evt)
     return QObject::eventFilter(obj, evt);
 }
 
+LabelOutOfFocusEventFilter::LabelOutOfFocusEventFilter(QObject* parent)
+    : QObject(parent)
+{
+}
+
+bool LabelOutOfFocusEventFilter::eventFilter(QObject* watched, QEvent* event)
+{
+    if (event->type() == QEvent::FocusOut) {
+        auto focus_out = static_cast<QFocusEvent*>(event);
+        if (focus_out->reason() != Qt::PopupFocusReason) {
+            auto label = qobject_cast<QLabel*>(watched);
+            if (label) {
+                auto flags = label->textInteractionFlags();
+                label->setTextInteractionFlags(Qt::NoTextInteraction);
+                label->setTextInteractionFlags(flags);
+            }
+        }
+    }
+
+    return QObject::eventFilter(watched, event);
+}
+
 void TableViewLastColumnResizingFixer::connectViewHeadersSignals()
 {
     connect(tableView->horizontalHeader(), &QHeaderView::sectionResized, this, &TableViewLastColumnResizingFixer::on_sectionResized);

src/qt/guiutil.h

@@ -161,6 +161,21 @@ namespace GUIUtil
         int size_threshold;
     };
 
+    /**
+     * Qt event filter that intercepts QEvent::FocusOut events for QLabel objects, and
+     * resets their `textInteractionFlags' property to get rid of the visible cursor.
+     *
+     * This is a temporary fix of QTBUG-59514.
+     */
+    class LabelOutOfFocusEventFilter : public QObject
+    {
+        Q_OBJECT
+
+    public:
+        explicit LabelOutOfFocusEventFilter(QObject* parent);
+        bool eventFilter(QObject* watched, QEvent* event) override;
+    };
+
     /**
      * Makes a QTableView last column feel as if it was being resized from its left border.
      * Also makes sure the column widths are never larger than the table's viewport.