Fix resolve() on fonts returned from QWidget::font()

Set the inherited properties as resolved on the font, so non-default
values are passed on in contexts that does resolve logic like QPainter.

One test is updated as it actually tests what it is supposed to on
more configurations.

Fixes: QTBUG-39560
Change-Id: Ief668e992ccdc091337a259a4c1306a00e67c73f
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/widgets/kernel/qwidget.cpp

@@ -247,6 +247,7 @@ QWidgetPrivate::QWidgetPrivate(int version)
 #ifndef QT_NO_TOOLTIP
       , toolTipDuration(-1)
 #endif
+      , directFontResolveMask(0)
       , inheritedFontResolveMask(0)
       , inheritedPaletteResolveMask(0)
       , leftmargin(0)
@@ -4751,6 +4752,18 @@ QFont QWidgetPrivate::naturalWidgetFont(uint inheritedMask) const
     return naturalFont;
 }
 
+/*!
+    \internal
+
+    Returns a font suitable for inheritance, where only locally set attributes are considered resolved.
+*/
+QFont QWidgetPrivate::localFont() const
+{
+    QFont localfont = data.fnt;
+    localfont.resolve(directFontResolveMask);
+    return localfont;
+}
+
 /*!
     \internal
 
@@ -4762,7 +4775,7 @@ QFont QWidgetPrivate::naturalWidgetFont(uint inheritedMask) const
 void QWidgetPrivate::resolveFont()
 {
     QFont naturalFont = naturalWidgetFont(inheritedFontResolveMask);
-    QFont resolvedFont = data.fnt.resolve(naturalFont);
+    QFont resolvedFont = localFont().resolve(naturalFont);
     setFont_helper(resolvedFont);
 }
 
@@ -4801,6 +4814,11 @@ void QWidgetPrivate::updateFont(const QFont &font)
         inheritedFontResolveMask = 0;
     }
     uint newMask = data.fnt.resolve() | inheritedFontResolveMask;
+    // Set the font as also having resolved inherited traits, so the result of reading QWidget::font()
+    // isn't all weak information, but save the original mask to be able to let new changes on the
+    // parent widget font propagate correctly.
+    directFontResolveMask = data.fnt.resolve();
+    data.fnt.resolve(newMask);
 
     for (int i = 0; i < children.size(); ++i) {
         QWidget *w = qobject_cast<QWidget*>(children.at(i));

src/widgets/kernel/qwidget_p.h

@@ -383,10 +383,11 @@ public:
 
     void updateFont(const QFont &);
     inline void setFont_helper(const QFont &font) {
-        if (data.fnt.resolve() == font.resolve() && data.fnt == font)
+        if (directFontResolveMask == font.resolve() && data.fnt == font)
             return;
         updateFont(font);
     }
+    QFont localFont() const;
     void resolveFont();
     QFont naturalWidgetFont(uint inheritedMask) const;
 
@@ -729,6 +730,7 @@ public:
 #endif
 
     // Other variables.
+    uint directFontResolveMask;
     uint inheritedFontResolveMask;
     uint inheritedPaletteResolveMask;
     short leftmargin;

src/widgets/styles/qstylesheetstyle.cpp

@@ -2642,7 +2642,7 @@ void QStyleSheetStyle::setPalette(QWidget *w)
         QRenderRule rule = renderRule(w, PseudoElement_None, map[i].state | extendedPseudoClass(w));
         if (i == 0) {
             if (!w->property("_q_styleSheetWidgetFont").isValid()) {
-                saveWidgetFont(w, w->font());
+                saveWidgetFont(w, w->d_func()->localFont());
             }
             updateStyleSheetFont(w);
             if (ew != w)
@@ -6025,7 +6025,7 @@ void QStyleSheetStyle::updateStyleSheetFont(QWidget* w) const
         unsetStyleSheetFont(w);
 
         if (rule.font.resolve()) {
-            QFont wf = w->font();
+            QFont wf = w->d_func()->localFont();
             styleSheetCaches->customFontWidgets.insert(w, {wf, rule.font.resolve()});
 
             QFont font = rule.font.resolve(wf);
@@ -6033,7 +6033,9 @@ void QStyleSheetStyle::updateStyleSheetFont(QWidget* w) const
             w->setFont(font);
         }
     } else {
-        QFont font = rule.font.resolve(w->font());
+        QFont wf = w->d_func()->localFont();
+        QFont font = rule.font.resolve(wf);
+        font.resolve(wf.resolve() | rule.font.resolve());
 
         if ((!w->isWindow() || w->testAttribute(Qt::WA_WindowPropagation))
             && isNaturalChild(w) && qobject_cast<QWidget *>(w->parent())) {
@@ -6041,10 +6043,11 @@ void QStyleSheetStyle::updateStyleSheetFont(QWidget* w) const
             font = font.resolve(static_cast<QWidget *>(w->parent())->font());
         }
 
-        if (w->data->fnt == font)
+        if (wf.resolve() == font.resolve() && wf == font)
             return;
 
         w->data->fnt = font;
+        w->d_func()->directFontResolveMask = font.resolve();
 
         QEvent e(QEvent::FontChange);
         QApplication::sendEvent(w, &e);

tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp

@@ -166,6 +166,7 @@ private slots:
     void getSetCheck();
     void fontPropagation();
     void fontPropagation2();
+    void fontPropagation3();
     void palettePropagation();
     void palettePropagation2();
     void enabledPropagation();
@@ -819,6 +820,18 @@ void tst_QWidget::fontPropagation2()
     QVERIFY(child5->font().italic());
 }
 
+void tst_QWidget::fontPropagation3()
+{
+    QWidget parent;
+    QWidget *child = new QWidget(&parent);
+    parent.setFont(QFont("Monospace", 9));
+    QImage image(32, 32, QImage::Format_RGB32);
+    QPainter p(&image);
+    p.setFont(child->font());
+    QCOMPARE(p.font().family(), child->font().family());
+    QCOMPARE(p.font().pointSize(), child->font().pointSize());
+}
+
 void tst_QWidget::palettePropagation()
 {
     QScopedPointer<QWidget> testWidget(new QWidget);

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

@@ -741,9 +741,9 @@ void tst_QStyleSheetStyle::fontPropagation()
     QCOMPARE(FONTSIZE(pb), 20);
 
     QWidget window;
-    window.setStyleSheet("* { font-size: 10pt }");
+    window.setStyleSheet("* { font-size: 9pt }");
     pb.setParent(&window);
-    QCOMPARE(FONTSIZE(pb), 10);
+    QCOMPARE(FONTSIZE(pb), 9);
     window.setStyleSheet("");
     QCOMPARE(FONTSIZE(pb), buttonFontSize);