Fix font and palette propagation for themed children created at runtime

Widgets have a default palette and font that is influenced by several
factors: theme, style, QApplication-wide overrides, and the parent's.
If an application sets a font or palette on a parent, then widgets
inherit those settings, no matter when they are added to the parent.

The bug is that this is not true for widgets that have an application-
wide override defined by the platform theme. For those, we need to merge
parent palette and font attributes with the theme, and this is currently
not done correctly, as the respective masks are not merged and inherited.

This change fixes this for fonts and palettes. Children are inheriting
their parent's inheritance masks, combined with the mask for the
attributes set explicitly on the parent. This makes the font and palette
resolving code correctly adopt those attributes that are set explicily,
while leaving everything else as per the theme override.

The test verifies that this works for children and grand children added
to a widget that has a palette or font set, both when themed and
unthemed. Children with own entries don't inherit from parent.

The QFont::resetFont test had to be changed, as it was testing the
wrong behavior. If the child would be added to the parent before the
font property was set, then the test would have failed. Since this
change makes sure that children inherit fonts in the same way, no
matter on when they are added to their parent, the test is now
modified to cover both cases, and ensures that they return identical
results.

[ChangeLog][QtWidgets][QWidget] Fonts and palette settings are inherited
by children from their parents even if the children have application-
wide platform theme overrides.

Change-Id: I179a652b735e85bba3fafc30098d08d61684f488
Fixes: QTBUG-82125
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Vitaly Fanaskov <vitaly.fanaskov@qt.io>

1 files changed, 126 insertions, 2 deletions

diff --git a/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp b/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
index 31e77b2a62..f0c490b598 100644
--- a/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
+++ b/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
@@ -162,8 +162,10 @@ private slots:
     void fontPropagation();
     void fontPropagation2();
     void fontPropagation3();
+    void fontPropagationDynamic();
     void palettePropagation();
     void palettePropagation2();
+    void palettePropagationDynamic();
     void enabledPropagation();
     void ignoreKeyEventsWhenDisabled_QTBUG27417();
     void properTabHandlingWhenDisabled_QTBUG27417();
@@ -831,6 +833,66 @@ void tst_QWidget::fontPropagation3()
     QCOMPARE(p.font().pointSize(), child->font().pointSize());
 }
 
+/*!
+    This tests that children that are added to a widget with an explicitly
+    defined font inherit that font correctly, merging (and overriding)
+    with the font that might be defined by the platform theme.
+*/
+void tst_QWidget::fontPropagationDynamic()
+{
+    // override side effects from previous tests
+    QFont themedFont;
+    themedFont.setBold(true);
+    themedFont.setPointSize(42);
+    QApplication::setFont(themedFont, "QPropagationTestWidget");
+
+    QWidget parent;
+    QWidget firstChild(&parent);
+
+    const QFont defaultFont = parent.font();
+    QFont appFont = defaultFont;
+    appFont.setPointSize(72);
+
+    // sanity check
+    QVERIFY(themedFont != defaultFont);
+    QVERIFY(themedFont != appFont);
+
+    // palette propagates to existing children
+    parent.setFont(appFont);
+    QCOMPARE(firstChild.font().pointSize(), appFont.pointSize());
+
+    // palatte propagates to children added later
+    QWidget secondChild(&parent);
+    QCOMPARE(secondChild.font().pointSize(), appFont.pointSize());
+    QWidget thirdChild;
+    QCOMPARE(thirdChild.font().pointSize(), defaultFont.pointSize());
+    thirdChild.setParent(&parent);
+    QCOMPARE(thirdChild.font().pointSize(), appFont.pointSize());
+
+    // even if the child has an override in QApplication::font
+    QPropagationTestWidget themedChild;
+    themedChild.ensurePolished(); // needed for default font to be set up
+    QCOMPARE(themedChild.font().pointSize(), themedFont.pointSize());
+    QCOMPARE(themedChild.font().bold(), themedFont.bold());
+    themedChild.setParent(&parent);
+    QCOMPARE(themedChild.font().pointSize(), appFont.pointSize());
+    QCOMPARE(themedChild.font().bold(), themedFont.bold());
+
+    // grand children as well
+    QPropagationTestWidget themedGrandChild;
+    themedGrandChild.setParent(&themedChild);
+    QCOMPARE(themedGrandChild.font().pointSize(), appFont.pointSize());
+    QCOMPARE(themedGrandChild.font().bold(), themedFont.bold());
+
+    // child with own font attribute does not inherit from parent
+    QFont childFont = defaultFont;
+    childFont.setPointSize(9);
+    QWidget modifiedChild;
+    modifiedChild.setFont(childFont);
+    modifiedChild.setParent(&parent);
+    QCOMPARE(modifiedChild.font().pointSize(), childFont.pointSize());
+}
+
 void tst_QWidget::palettePropagation()
 {
     QScopedPointer<QWidget> testWidget(new QWidget);
@@ -875,8 +937,8 @@ void tst_QWidget::palettePropagation2()
 
     // ! Note, the code below is executed in tst_QWidget's constructor.
     // QPalette palette;
-    // font.setColor(QPalette::ToolTipBase, QColor(12, 13, 14));
-    // font.setColor(QPalette::Text, QColor(21, 22, 23));
+    // palette.setColor(QPalette::ToolTipBase, QColor(12, 13, 14));
+    // palette.setColor(QPalette::Text, QColor(21, 22, 23));
     // qApp->setPalette(palette, "QPropagationTestWidget");
 
     QScopedPointer<QWidget> root(new QWidget);
@@ -975,6 +1037,68 @@ void tst_QWidget::palettePropagation2()
     QCOMPARE(child5->palette().color(QPalette::ToolTipText), sysPalButton);
 }
 
+/*!
+    This tests that children that are added to a widget with an explicitly
+    defined palette inherit that palette correctly, merging (and overriding)
+    with the palette that might be defined by the platform theme.
+*/
+void tst_QWidget::palettePropagationDynamic()
+{
+    // override side effects from previous tests
+    QPalette themedPalette;
+    themedPalette.setColor(QPalette::ToolTipBase, QColor(12, 13, 14));
+    themedPalette.setColor(QPalette::Text, QColor(21, 22, 23));
+    QApplication::setPalette(themedPalette, "QPropagationTestWidget");
+
+    QWidget parent;
+    QWidget firstChild(&parent);
+
+    const QPalette defaultPalette = parent.palette();
+    QPalette appPalette = defaultPalette;
+    const QColor appColor(1, 2, 3);
+    appPalette.setColor(QPalette::Text, appColor);
+
+    // sanity check
+    QVERIFY(themedPalette != defaultPalette);
+    QVERIFY(themedPalette != appPalette);
+
+    // palette propagates to existing children
+    parent.setPalette(appPalette);
+    QCOMPARE(firstChild.palette().color(QPalette::Text), appPalette.color(QPalette::Text));
+
+    // palatte propagates to children added later
+    QWidget secondChild(&parent);
+    QCOMPARE(secondChild.palette().color(QPalette::Text), appPalette.color(QPalette::Text));
+    QWidget thirdChild;
+    QCOMPARE(thirdChild.palette().color(QPalette::Text), defaultPalette.color(QPalette::Text));
+    thirdChild.setParent(&parent);
+    QCOMPARE(thirdChild.palette().color(QPalette::Text), appPalette.color(QPalette::Text));
+
+    // even if the child has an override in QApplication::palette
+    QPropagationTestWidget themedChild;
+    themedChild.ensurePolished(); // needed for default palette to be set up
+    QCOMPARE(themedChild.palette().color(QPalette::Text), themedPalette.color(QPalette::Text));
+    QCOMPARE(themedChild.palette().color(QPalette::ToolTipBase), themedPalette.color(QPalette::ToolTipBase));
+    themedChild.setParent(&parent);
+    QCOMPARE(themedChild.palette().color(QPalette::Text), appPalette.color(QPalette::Text));
+    QCOMPARE(themedChild.palette().color(QPalette::ToolTipBase), themedPalette.color(QPalette::ToolTipBase));
+
+    // grand children as well
+    QPropagationTestWidget themedGrandChild;
+    themedGrandChild.setParent(&themedChild);
+    QCOMPARE(themedGrandChild.palette().color(QPalette::Text), appPalette.color(QPalette::Text));
+    QCOMPARE(themedGrandChild.palette().color(QPalette::ToolTipBase), themedPalette.color(QPalette::ToolTipBase));
+
+    // child with own color does not inherit from parent
+    QPalette childPalette = defaultPalette;
+    childPalette.setColor(QPalette::Text, Qt::red);
+    QWidget modifiedChild;
+    modifiedChild.setPalette(childPalette);
+    modifiedChild.setParent(&parent);
+    QCOMPARE(modifiedChild.palette().color(QPalette::Text), childPalette.color(QPalette::Text));
+
+}
+
 void tst_QWidget::enabledPropagation()
 {
     QScopedPointer<QWidget> testWidget(new QWidget);