QTabBar: take a style sheet's font into account when laying out tabs

If a tab has a font assigned to it through a style sheet, then take the
font size into account when calculating the contents rectangle.

Add a test, which hardcodes the windows style to avoid flaky behavior
when e.g. macOS lays tabs out in the center.

Fixes: QTBUG-92988
Change-Id: Ifb0ac97db7647cc25367972737be8878e50f6040
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
(cherry picked from commit e3b2b12a912361af309302a4b1fc27c2206322af)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/styles/qstylesheetstyle.cpp

@@ -5220,15 +5220,26 @@ QSize QStyleSheetStyle::sizeFromContents(ContentsType ct, const QStyleOption *op
 #if QT_CONFIG(tabbar)
     case CT_TabBarTab: {
         QRenderRule subRule = renderRule(w, opt, PseudoElement_TabBarTab);
-        if (subRule.hasBox() || !subRule.hasNativeBorder()) {
+        if (subRule.hasBox() || !subRule.hasNativeBorder() || subRule.hasFont) {
             int spaceForIcon = 0;
             bool vertical = false;
+            QString text;
             if (const QStyleOptionTab *tab = qstyleoption_cast<const QStyleOptionTab *>(opt)) {
                 if (!tab->icon.isNull())
                     spaceForIcon = 6 /* icon offset */ + 4 /* spacing */ + 2 /* magic */; // ###: hardcoded to match with common style
                 vertical = verticalTabs(tab->shape);
+                text = tab->text;
+            }
+            if (subRule.hasBox() || !subRule.hasNativeBorder())
+                sz = csz + QSize(vertical ? 0 : spaceForIcon, vertical ? spaceForIcon : 0);
+            if (subRule.hasFont) {
+                QFont ruleFont = subRule.font.resolve(w->font());
+                QFontMetrics fm(ruleFont);
+                const QSize textSize = fm.size(Qt::TextShowMnemonic, text)
+                                     + QSize(pixelMetric(PM_TabBarTabHSpace, opt, w),
+                                             pixelMetric(PM_TabBarTabVSpace, opt, w));
+                sz = sz.expandedTo(vertical ? textSize.transposed() : textSize);
             }
-            sz = csz + QSize(vertical ? 0 : spaceForIcon, vertical ? spaceForIcon : 0);
             return subRule.boxSize(subRule.adjustSize(sz));
         }
         sz = subRule.adjustSize(csz);
@@ -6058,13 +6069,17 @@ QRect QStyleSheetStyle::subElementRect(SubElement se, const QStyleOption *opt, c
     case SE_TabBarTabLeftButton:
     case SE_TabBarTabRightButton: {
         QRenderRule subRule = renderRule(w, opt, PseudoElement_TabBarTab);
-        if (subRule.hasBox() || !subRule.hasNativeBorder()) {
+        if (subRule.hasBox() || !subRule.hasNativeBorder() || subRule.hasFont) {
             if (se == SE_TabBarTabText) {
                 if (const QStyleOptionTab *tab = qstyleoption_cast<const QStyleOptionTab *>(opt)) {
                     const QTabBar *bar = qobject_cast<const QTabBar *>(w);
                     const QRect optRect = bar && tab->tabIndex != -1 ? bar->tabRect(tab->tabIndex) : opt->rect;
                     const QRect r = positionRect(w, subRule, PseudoElement_TabBarTab, optRect, opt->direction);
                     QStyleOptionTab tabCopy(*tab);
+                    if (subRule.hasFont) {
+                        const QFont ruleFont = w ? subRule.font.resolve(w->font()) : subRule.font;
+                        tabCopy.fontMetrics = QFontMetrics(ruleFont);
+                    }
                     tabCopy.rect = subRule.contentsRect(r);
                     return ParentStyle::subElementRect(se, &tabCopy, w);
                 }

tests/auto/widgets/styles/qstylesheetstyle/tst_qstylesheetstyle.cpp

@@ -106,6 +106,8 @@ private slots:
 #endif
     void background();
     void tabAlignment();
+    void tabFont_data();
+    void tabFont();
     void attributesList();
     void minmaxSizes();
     void task206238_twice();
@@ -1179,6 +1181,71 @@ void tst_QStyleSheetStyle::tabAlignment()
     QVERIFY(bar->geometry().top() > 100);
 }
 
+void tst_QStyleSheetStyle::tabFont_data()
+{
+    QTest::addColumn<int>("pixelSize");
+    QTest::addColumn<QTabWidget::TabPosition>("tabPosition");
+
+    QTest::newRow("medium, horizontal") << 24 << QTabWidget::North;
+    QTest::newRow("large, vertical") << 36 << QTabWidget::West;
+}
+
+#include <QApplication>
+
+void tst_QStyleSheetStyle::tabFont()
+{
+    QFETCH(int, pixelSize);
+    QFETCH(QTabWidget::TabPosition, tabPosition);
+    const bool vertical = tabPosition == QTabWidget::West || tabPosition == QTabWidget::East;
+
+    // macOS style centers tabs and messes up the test
+    QWindowsStyle windowsStyle;
+    QWidget topLevel;
+    topLevel.setStyle(&windowsStyle);
+    topLevel.setWindowTitle(QTest::currentTestFunction());
+    QTabWidget tabWidget;
+    tabWidget.setStyle(&windowsStyle);
+    tabWidget.addTab(new QWidget,"Tab title");
+    tabWidget.setTabPosition(tabPosition);
+    QTabWidget styledWidget;
+    styledWidget.setStyle(&windowsStyle);
+    styledWidget.setTabPosition(tabPosition);
+    styledWidget.addTab(new QWidget,"Tab title");
+
+    QTabBar *bar = tabWidget.tabBar();
+    QTabBar *styledBar = styledWidget.tabBar();
+    QVERIFY(bar && styledBar);
+    bar->setStyle(&windowsStyle);
+    styledBar->setStyle(&windowsStyle);
+
+    QBoxLayout box(vertical ? QBoxLayout::LeftToRight : QBoxLayout::TopToBottom);
+    box.addWidget(&tabWidget);
+    box.addWidget(&styledWidget);
+    topLevel.setLayout(&box);
+
+    topLevel.resize(600, 600);
+    centerOnScreen(&topLevel);
+    topLevel.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&topLevel));
+
+    const QRect defaultRect = bar->tabRect(0);
+    QCOMPARE(styledBar->tabRect(0), defaultRect);
+
+    QFont font;
+    font.setPointSize(pixelSize);
+    tabWidget.setFont(font);
+
+    const QRect rectWithFont = bar->tabRect(0);
+    if (vertical)
+        QVERIFY(rectWithFont.height() > defaultRect.height());
+    else
+        QVERIFY(rectWithFont.width() > defaultRect.width());
+
+    styledWidget.setStyleSheet(QString("QTabBar { font-size: %1pt; }").arg(pixelSize));
+    const QRect rectWithStyle = styledBar->tabRect(0);
+    QCOMPARE(rectWithStyle.size(), rectWithFont.size());
+}
+
 void tst_QStyleSheetStyle::attributesList()
 {
     const QColor blue(Qt::blue);