Show line indicator instead of rectangle while dragging in tables (#5252)

src/widgets/helper/TableStyles.hpp

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <QProxyStyle>
+
+class QTableView;
+
+namespace chatterino {
+
+/// @brief A custom style for drag operations of rows on tables
+///
+/// This style overwrites how `PE_IndicatorItemViewItemDrop`, the drop
+/// indicator of item-views, is drawn. It's intended to be used on QTableViews
+/// where entire rows are moved (not individual cells). The indicator is shown
+/// as a line at the position where the dragged item should be inserted. If no
+/// such position exists, a red border is drawn around the viewport.
+class TableRowDragStyle : public QProxyStyle
+{
+public:
+    /// Applies the style to @a view
+    static void applyTo(QTableView *view);
+
+    void drawPrimitive(QStyle::PrimitiveElement element,
+                       const QStyleOption *option, QPainter *painter,
+                       const QWidget *widget = nullptr) const override;
+
+private:
+    /// @param target The style to wrap. This is **not** the parent of this
+    ///               object. This object will become the parent of @a target.
+    TableRowDragStyle(QStyle *target);
+};
+
+}  // namespace chatterino