Introduce layer window rule

The new window rule allows to overwrite the stack layer. It can be
useful on wayland to force picture-in-picture surfaces (which are
xdg-toplevels at the moment) to be placed above fullscreen windows.
Keep above flag is unsuitable because fullscreen windows are placed
higher "above" windows.

CCBUG: 466016

autotests/integration/dbus_interface_test.cpp

@@ -140,6 +140,7 @@ void TestDbusInterface::testGetWindowInfoXdgShellClient()
 #if KWIN_BUILD_ACTIVITIES
         {QStringLiteral("activities"), QStringList()},
 #endif
+        {QStringLiteral("layer"), NormalLayer},
     };
 
     // let's get the window info
@@ -276,6 +277,7 @@ void TestDbusInterface::testGetWindowInfoX11Client()
 #if KWIN_BUILD_ACTIVITIES
         {QStringLiteral("activities"), QStringList()},
 #endif
+        {QStringLiteral("layer"), NormalLayer},
     };
 
     // let's get the window info

autotests/integration/xdgshellwindow_rules_test.cpp

@@ -151,6 +151,10 @@ private Q_SLOTS:
     void testScreenApplyNow();
     void testScreenForceTemporarily();
 
+    void testLayerDontAffect();
+    void testLayerForce();
+    void testLayerForceTemporarily();
+
     void testMatchAfterNameChange();
 
 private:
@@ -2980,5 +2984,42 @@ void TestXdgShellWindowRules::testMatchAfterNameChange()
     QCOMPARE(window->keepAbove(), true);
 }
 
+void TestXdgShellWindowRules::testLayerDontAffect()
+{
+    setWindowRule("layer", QStringLiteral("overlay"), int(Rules::DontAffect));
+
+    createTestWindow();
+
+    // The layer should not be affected by the rule.
+    QCOMPARE(m_window->layer(), NormalLayer);
+
+    destroyTestWindow();
+}
+
+void TestXdgShellWindowRules::testLayerForce()
+{
+    setWindowRule("layer", QStringLiteral("overlay"), int(Rules::Force));
+
+    createTestWindow();
+    QCOMPARE(m_window->layer(), UnmanagedLayer);
+
+    destroyTestWindow();
+}
+
+void TestXdgShellWindowRules::testLayerForceTemporarily()
+{
+    setWindowRule("layer", QStringLiteral("overlay"), int(Rules::ForceTemporarily));
+
+    createTestWindow();
+    QCOMPARE(m_window->layer(), UnmanagedLayer);
+
+    // The rule should be discarded when the window is closed.
+    destroyTestWindow();
+    createTestWindow();
+    QCOMPARE(m_window->layer(), NormalLayer);
+
+    destroyTestWindow();
+}
+
 WAYLANDTEST_MAIN(TestXdgShellWindowRules)
 #include "xdgshellwindow_rules_test.moc"

src/dbusinterface.cpp

@@ -180,6 +180,7 @@ QVariantMap clientToVariantMap(const Window *c)
 #if KWIN_BUILD_ACTIVITIES
             {QStringLiteral("activities"), c->activities()},
 #endif
+            {QStringLiteral("layer"), c->layer()},
     };
 }
 }

src/kcms/rules/rulesmodel.cpp

@@ -719,6 +719,12 @@ void RulesModel::populateRuleList()
                          RulePolicy::ForceRule, RuleItem::Boolean,
                          i18n("Block compositing"), i18n("Appearance & Fixes"),
                          QIcon::fromTheme("composite-track-on")));
+
+    auto layer = addRule(new RuleItem(QLatin1String("layer"),
+                                      RulePolicy::ForceRule, RuleItem::Option,
+                                      i18n("Layer"), i18n("Appearance & Fixes"),
+                                      QIcon::fromTheme("view-sort")));
+    layer->setOptionsData(layerModelData());
 }
 
 const QHash<QString, QString> RulesModel::x11PropertyHash()
@@ -741,6 +747,7 @@ const QHash<QString, QString> RulesModel::x11PropertyHash()
         {"type", "type"},
         {"desktopFile", "desktopfile"},
         {"desktops", "desktops"},
+        {"layer", "layer"},
     };
     return propertyToRule;
 };
@@ -911,6 +918,23 @@ QList<OptionsModel::Data> RulesModel::colorSchemesModelData() const
     return modelData;
 }
 
+QList<OptionsModel::Data> RulesModel::layerModelData() const
+{
+    static const auto modelData = QList<OptionsModel::Data>{
+        {DesktopLayer, i18n("Desktop")},
+        {BelowLayer, i18n("Below")},
+        {NormalLayer, i18n("Normal")},
+        {AboveLayer, i18n("Above")},
+        {NotificationLayer, i18n("Notification")},
+        {ActiveLayer, i18n("Fullscreen")},
+        {PopupLayer, i18n("Popup")},
+        {CriticalNotificationLayer, i18n("Critical Notification")},
+        {OnScreenDisplayLayer, i18n("OSD")},
+        {UnmanagedLayer, i18n("Overlay")},
+    };
+    return modelData;
+}
+
 void RulesModel::detectWindowProperties(int miliseconds)
 {
     QTimer::singleShot(miliseconds, this, &RulesModel::selectX11Window);

src/kcms/rules/rulesmodel.h

@@ -102,6 +102,7 @@ private:
     QList<OptionsModel::Data> placementModelData() const;
     QList<OptionsModel::Data> focusModelData() const;
     QList<OptionsModel::Data> colorSchemesModelData() const;
+    QList<OptionsModel::Data> layerModelData() const;
 
 private Q_SLOTS:
     void selectX11Window();

src/rules.cpp

@@ -33,7 +33,8 @@ namespace KWin
 {
 
 Rules::Rules()
-    : wmclassmatch(UnimportantMatch)
+    : layerrule(UnusedForceRule)
+    , wmclassmatch(UnimportantMatch)
     , wmclasscomplete(UnimportantMatch)
     , windowrolematch(UnimportantMatch)
     , titlematch(UnimportantMatch)
@@ -160,6 +161,7 @@ void Rules::readFromSettings(const RuleSettings *settings)
     READ_SET_RULE(shortcut);
     READ_FORCE_RULE(disableglobalshortcuts, );
     READ_SET_RULE(desktopfile);
+    READ_FORCE_RULE(layer, );
 }
 
 #undef READ_MATCH_STRING
@@ -238,6 +240,7 @@ void Rules::write(RuleSettings *settings) const
     WRITE_SET_RULE(shortcut, Shortcut, );
     WRITE_FORCE_RULE(disableglobalshortcuts, Disableglobalshortcuts, );
     WRITE_SET_RULE(desktopfile, Desktopfile, );
+    WRITE_FORCE_RULE(layer, Layer, );
 }
 
 #undef WRITE_MATCH_STRING
@@ -282,7 +285,8 @@ bool Rules::isEmpty() const
             && strictgeometryrule == UnusedForceRule
             && shortcutrule == UnusedSetRule
             && disableglobalshortcutsrule == UnusedForceRule
-            && desktopfilerule == UnusedSetRule);
+            && desktopfilerule == UnusedSetRule
+            && layerrule == UnusedForceRule);
 }
 
 Rules::ForceRule Rules::convertForceRule(int v)
@@ -575,6 +579,7 @@ APPLY_RULE(ignoregeometry, IgnoreGeometry, bool)
 APPLY_RULE(screen, Screen, int)
 APPLY_RULE(activity, Activity, QStringList)
 APPLY_FORCE_RULE(type, Type, NET::WindowType)
+APPLY_FORCE_RULE(layer, Layer, enum Layer)
 
 bool Rules::applyDesktops(QList<VirtualDesktop *> &vds, bool init) const
 {
@@ -698,6 +703,7 @@ bool Rules::discardUsed(bool withdrawn)
     DISCARD_USED_SET_RULE(shortcut);
     DISCARD_USED_FORCE_RULE(disableglobalshortcuts);
     DISCARD_USED_SET_RULE(desktopfile);
+    DISCARD_USED_FORCE_RULE(layer);
 
     return changed;
 }
@@ -845,6 +851,7 @@ CHECK_FORCE_RULE(StrictGeometry, bool)
 CHECK_RULE(Shortcut, QString)
 CHECK_FORCE_RULE(DisableGlobalShortcuts, bool)
 CHECK_RULE(DesktopFile, QString)
+CHECK_FORCE_RULE(Layer, Layer)
 
 #undef CHECK_RULE
 #undef CHECK_FORCE_RULE

src/rules.h

@@ -77,6 +77,7 @@ public:
     QString checkShortcut(QString s, bool init = false) const;
     bool checkDisableGlobalShortcuts(bool disable) const;
     QString checkDesktopFile(QString desktopFile, bool init = false) const;
+    Layer checkLayer(Layer layer) const;
 
 private:
     MaximizeMode checkMaximizeVert(MaximizeMode mode, bool init) const;
@@ -111,6 +112,7 @@ public:
         Activity = 1 << 16,
         Screen = 1 << 17,
         DesktopFile = 1 << 18,
+        Layer = 1 << 19,
         All = 0xffffffff
     };
     Q_DECLARE_FLAGS(Types, Type)
@@ -184,6 +186,7 @@ public:
     bool applyShortcut(QString &shortcut, bool init) const;
     bool applyDisableGlobalShortcuts(bool &disable) const;
     bool applyDesktopFile(QString &desktopFile, bool init) const;
+    bool applyLayer(enum Layer &layer) const;
 
 private:
 #endif
@@ -204,6 +207,8 @@ private:
     static bool checkSetStop(SetRule rule);
     static bool checkForceStop(ForceRule rule);
 #endif
+    enum Layer layer;
+    ForceRule layerrule;
     QString description;
     QString wmclass;
     StringMatch wmclassmatch;

src/rulesettings.kcfg

@@ -431,5 +431,26 @@
       <max code="true">static_cast&lt;Rules::SetRule&gt;(Rules::ForceTemporarily)</max>
       <default code="true">Rules::UnusedSetRule</default>
     </entry>
+
+    <entry name="layer" type="Enum">
+      <label>Layer</label>
+      <choices name="KWin::Layer">
+        <choice name="DesktopLayer" value="desktop" />
+        <choice name="BelowLayer" value="below" />
+        <choice name="NormalLayer" value="normal" />
+        <choice name="AboveLayer" value="above" />
+        <choice name="NotificationLayer" value="notification" />
+        <choice name="ActiveLayer" value="fullscreen" />
+        <choice name="PopupLayer" value="popup" />
+        <choice name="CriticalNotificationLayer" value="critical-notification" />
+        <choice name="OnScreenDisplayLayer" value="osd" />
+        <choice name="UnmanagedLayer" value="overlay" />
+      </choices>
+      <default code="true">NormalLayer</default>
+    </entry>
+    <entry name="layerrule" type="Int">
+      <label>Layer rule type</label>
+      <default code="true">Rules::UnusedForceRule</default>
+    </entry>
   </group>
 </kcfg>

src/window.cpp

@@ -552,7 +552,7 @@ void Window::markAsDeleted()
 Layer Window::layer() const
 {
     if (m_layer == UnknownLayer) {
-        const_cast<Window *>(this)->m_layer = belongsToLayer();
+        const_cast<Window *>(this)->m_layer = rules()->checkLayer(belongsToLayer());
     }
     return m_layer;
 }
@@ -562,7 +562,7 @@ void Window::updateLayer()
     if (isDeleted()) {
         return;
     }
-    if (layer() == belongsToLayer()) {
+    if (layer() == rules()->checkLayer(belongsToLayer())) {
         return;
     }
     StackingUpdatesBlocker blocker(workspace());
@@ -4139,6 +4139,7 @@ void Window::applyWindowRules()
     setFullScreen(isRequestedFullScreen());
     setNoBorder(noBorder());
     updateColorScheme();
+    updateLayer();
     // FSP
     // AcceptFocus :
     if (workspace()->mostRecentlyActivatedWindow() == this