Improve handling of minimumHeightForWidth()

This also aligns the implementation with QWidgetItem::heightForWidth()

Fixes: QTBUG-92599
Change-Id: I0de68c61ec37a16a8c338575d07ff9e8168a0b98
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>
(cherry picked from commit 4d4eb11fe340bf0b3a1ce0caae62d9319bf941cf)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/kernel/qboxlayout.cpp

@@ -63,7 +63,7 @@ struct QBoxLayoutItem
     }
     int mhfw(int w) {
         if (item->hasHeightForWidth()) {
-            return item->heightForWidth(w);
+            return item->minimumHeightForWidth(w);
         } else {
             return item->minimumSize().height();
         }

src/widgets/kernel/qlayout.cpp

@@ -604,6 +604,28 @@ void QLayout::childEvent(QChildEvent *e)
         removeItem(childLayout);
 }
 
+/*!
+  \internal
+  Also takes contentsMargins and menu bar into account.
+*/
+int QLayout::totalMinimumHeightForWidth(int w) const
+{
+    Q_D(const QLayout);
+    int side=0, top=0;
+    if (d->topLevel) {
+        QWidget *parent = parentWidget();
+        parent->ensurePolished();
+        QWidgetPrivate *wd = parent->d_func();
+        side += wd->leftmargin + wd->rightmargin;
+        top += wd->topmargin + wd->bottommargin;
+    }
+    int h = minimumHeightForWidth(w - side) + top;
+#if QT_CONFIG(menubar)
+    h += menuBarHeightForWidth(d->menubar, w);
+#endif
+    return h;
+}
+
 /*!
   \internal
   Also takes contentsMargins and menu bar into account.

src/widgets/kernel/qlayout.h

@@ -127,6 +127,7 @@ public:
     virtual QLayoutItem *replaceWidget(QWidget *from, QWidget *to,
                                        Qt::FindChildOptions options = Qt::FindChildrenRecursively);
 
+    int totalMinimumHeightForWidth(int w) const;
     int totalHeightForWidth(int w) const;
     QSize totalMinimumSize() const;
     QSize totalMaximumSize() const;

src/widgets/kernel/qlayoutitem.cpp

@@ -575,6 +575,36 @@ int QWidgetItem::heightForWidth(int w) const
     return hfw;
 }
 
+int QWidgetItem::minimumHeightForWidth(int w) const
+{
+    if (isEmpty())
+        return -1;
+
+    w = !wid->testAttribute(Qt::WA_LayoutUsesWidgetRect)
+      ? fromLayoutItemSize(wid->d_func(), QSize(w, 0)).width()
+      : w;
+
+    int hfw;
+    if (wid->layout())
+        hfw = wid->layout()->totalMinimumHeightForWidth(w);
+    else
+        hfw = wid->heightForWidth(w);   // QWidget doesn't have minimumHeightForWidth()
+
+    if (hfw > wid->maximumHeight())
+        hfw = wid->maximumHeight();
+    if (hfw < wid->minimumHeight())
+        hfw = wid->minimumHeight();
+
+    hfw = !wid->testAttribute(Qt::WA_LayoutUsesWidgetRect)
+        ? toLayoutItemSize(wid->d_func(), QSize(0, hfw)).height()
+        : hfw;
+
+    if (hfw < 0)
+        hfw = 0;
+    return hfw;
+
+}
+
 /*!
     \reimp
 */

src/widgets/kernel/qlayoutitem.h

@@ -137,6 +137,7 @@ public:
 
     bool hasHeightForWidth() const override;
     int heightForWidth(int) const override;
+    int minimumHeightForWidth(int) const override;
     QSizePolicy::ControlTypes controlTypes() const override;
 protected:
     QWidget *wid;