Introduce SH_TitleBar_ShowToolTipsOnButtons style hint

This removes some tight coupling between QMdiSubWindow and
QMacStyle in order to allow the latter to be moved into a plugin.

Change-Id: I090c2c5774279c0454486c3db2e77f00a646b145
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@qt.io>

src/widgets/doc/src/widgets-and-layouts/stylesheet.qdoc

@@ -2433,6 +2433,12 @@
            See also
            \l{Qt Style Sheets Reference#subcontrol-origin-prop}{subcontrol-origin}.
 
+    \row
+        \li \b{\c titlebar-show-tooltips-on-buttons}}
+            \target titlebar-show-tooltips-on-buttons-prop
+        \li \c bool
+        \li Whether tool tips are shown on window title bar buttons.
+
     \row
         \li \b{\c text-align} \target text-align-prop
         \li \l{#Alignment}{Alignment}

src/widgets/styles/qcommonstyle.cpp

@@ -5231,6 +5231,9 @@ int QCommonStyle::styleHint(StyleHint sh, const QStyleOption *opt, const QWidget
         ret = QAbstractItemView::ScrollPerItem;
         break;
 #endif
+    case SH_TitleBar_ShowToolTipsOnButtons:
+        ret = true;
+        break;
     default:
         ret = 0;
         break;

src/widgets/styles/qmacstyle_mac.mm

@@ -3025,6 +3025,10 @@ int QMacStyle::styleHint(StyleHint sh, const QStyleOption *opt, const QWidget *w
     case SH_ItemView_ScrollMode:
         ret = QAbstractItemView::ScrollPerPixel;
         break;
+    case SH_TitleBar_ShowToolTipsOnButtons:
+        // min/max/close buttons on windows don't show tool tips
+        ret = false;
+        break;
     default:
         ret = QCommonStyle::styleHint(sh, opt, w, hret);
         break;

src/widgets/styles/qstyle.cpp

@@ -1987,6 +1987,11 @@ void QStyle::drawItemPixmap(QPainter *painter, const QRect &rect, int alignment,
            by the style. Can be overridden with QAbstractItemView::setVerticalScrollMode() and
            QAbstractItemView::setHorizontalScrollMode(). This enum value has been introduced in Qt 5.7.
 
+    \value SH_TitleBar_ShowToolTipsOnButtons
+           Determines if tool tips are shown on window title bar buttons.
+           The Mac style, for example, sets this to false.
+           This enum value has been introduced in Qt 5.10.
+
     \sa styleHint()
 */
 

src/widgets/styles/qstyle.h

@@ -737,6 +737,7 @@ public:
         SH_Menu_SubMenuResetWhenReenteringParent,
         SH_Menu_SubMenuDontStartSloppyOnLeave,
         SH_ItemView_ScrollMode,
+        SH_TitleBar_ShowToolTipsOnButtons,
         // Add new style hint values here
 
         SH_CustomBase = 0xf0000000

src/widgets/styles/qstylesheetstyle.cpp

@@ -679,6 +679,7 @@ static const char knownStyleHints[][45] = {
     "titlebar-minimize-icon",
     "titlebar-normal-icon",
     "titlebar-shade-icon",
+    "titlebar-show-tooltips-on-buttons",
     "titlebar-unshade-icon",
     "toolbutton-popup-delay",
     "trash-icon",
@@ -5317,6 +5318,7 @@ int QStyleSheetStyle::styleHint(StyleHint sh, const QStyleOption *opt, const QWi
                                    }
         case SH_ItemView_ArrowKeysNavigateIntoChildren: s = QLatin1String("arrow-keys-navigate-into-children"); break;
         case SH_ItemView_PaintAlternatingRowColorsForEmptyArea: s = QLatin1String("paint-alternating-row-colors-for-empty-area"); break;
+        case SH_TitleBar_ShowToolTipsOnButtons: s = QLatin1String("titlebar-show-tooltips-on-buttons"); break;
         default: break;
     }
     if (!s.isEmpty() && rule.hasStyleHint(s)) {

src/widgets/widgets/qmdisubwindow.cpp

@@ -158,9 +158,6 @@
 #include <QMainWindow>
 #include <QScrollBar>
 #include <QDebug>
-#if QT_CONFIG(style_mac)
-#include <private/qmacstyle_mac_p.h>
-#endif
 #include <QMdiArea>
 #include <QScopedValueRollback>
 
@@ -300,11 +297,8 @@ static void showToolTip(QHelpEvent *helpEvent, QWidget *widget, const QStyleOpti
     Q_ASSERT(helpEvent->type() == QEvent::ToolTip);
     Q_ASSERT(widget);
 
-#if QT_CONFIG(style_mac)
-    // Native Mac windows don't show tool tip.
-    if (qobject_cast<QMacStyle *>(widget->style()))
+    if (widget->style()->styleHint(QStyle::SH_TitleBar_ShowToolTipsOnButtons, &opt, widget))
         return;
-#endif
 
     // Convert CC_MdiControls to CC_TitleBar. Sub controls of different complex
     // controls cannot be in the same switch as they might have the same value.