Try to apply the colorscheme of the current theme to QIcons

Summary:
Before icons loaded internally with QIcon::fromTheme were being colored with the
colors from the current global color scheme instead of the ones from the current
Plasma Theme. Leading to visual bugs when the two differ. This happened because
KIconLoader uses the global color scheme by default.
A prominent case is the notification send by the network plasmoid when one
successfully connected to a wireless network. It sets the icon
"network-wireless-on" which is not included in Breeze icons (but is included in
Breeze Plasma Theme). If the current icon theme is indeed Breeze, IconItem
resorts to using QIcon::fromTheme and we end up with a wrong colored
"network-wireless" icon.

BUG: 417780

Test Plan:
{F8125752}

{F8125753}

Reviewers: #plasma, cblack, ngraham, mart

Reviewed By: #plasma, cblack, ngraham, mart

Subscribers: mart, wbauer, cblack, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D27589

src/declarativeimports/core/iconitem.cpp

@@ -22,6 +22,7 @@
 #include <QDebug>
 #include <QPaintEngine>
 #include <QPainter>
+#include <QPalette>
 #include <QPropertyAnimation>
 #include <QPixmap>
 #include <QSGSimpleTextureNode>
@@ -33,6 +34,7 @@
 
 #include "fadingnode_p.h"
 #include <QuickAddons/ManagedTextureNode>
+#include "theme.h"
 #include "units.h"
 
 IconItem::IconItem(QQuickItem *parent)
@@ -595,7 +597,9 @@ void IconItem::loadPixmap()
             result = m_svgIcon->pixmap();
         }
     } else if (!m_icon.isNull()) {
+        KIconLoader::global()->setCustomPalette(Plasma::Theme().palette());
         result = m_icon.pixmap(QSize(size, size) * (window() ? window()->devicePixelRatio() : qApp->devicePixelRatio()));
+        KIconLoader::global()->resetPalette();
     } else if (!m_imageIcon.isNull()) {
         result = QPixmap::fromImage(m_imageIcon);
     } else {

src/plasma/private/theme_p.cpp

@@ -400,6 +400,7 @@ void ThemePrivate::colorsChanged()
     buttonColorScheme = KColorScheme(QPalette::Active, KColorScheme::Button, colors);
     viewColorScheme = KColorScheme(QPalette::Active, KColorScheme::View, colors);
     selectionColorScheme = KColorScheme(QPalette::Active, KColorScheme::Selection, colors);
+    palette = KColorScheme::createApplicationPalette(colors);
     scheduleThemeChangeNotification(PixmapCache | SvgElementsCache);
     emit applicationPaletteChange();
 }
@@ -802,6 +803,7 @@ void ThemePrivate::setThemeName(const QString &tempThemeName, bool writeSettings
     buttonColorScheme = KColorScheme(QPalette::Active, KColorScheme::Button, colors);
     viewColorScheme = KColorScheme(QPalette::Active, KColorScheme::View, colors);
     complementaryColorScheme = KColorScheme(QPalette::Active, KColorScheme::Complementary, colors);
+    palette = KColorScheme::createApplicationPalette(colors);
     const QString wallpaperPath = QLatin1String(PLASMA_RELATIVE_DATA_INSTALL_DIR "/desktoptheme/") % theme % QLatin1String("/wallpapers/");
     hasWallpapers = !QStandardPaths::locate(QStandardPaths::GenericDataLocation, wallpaperPath, QStandardPaths::LocateDirectory).isEmpty();
 

src/plasma/private/theme_p.h

@@ -119,6 +119,7 @@ public:
     KColorScheme buttonColorScheme;
     KColorScheme viewColorScheme;
     KColorScheme complementaryColorScheme;
+    QPalette palette;
     bool eventFilter(QObject *watched, QEvent *event) override;
     KConfigGroup cfg;
     QString defaultWallpaperTheme;

src/plasma/theme.cpp

@@ -194,6 +194,12 @@ QString Theme::styleSheet(const QString &css) const
     return d->processStyleSheet(css, Svg::Status::Normal);
 }
 
+
+QPalette Theme::palette() const
+{
+    return d->palette;
+}
+
 QString Theme::wallpaperPath(const QSize &size) const
 {
     QString fullPath;

src/plasma/theme.h

@@ -67,6 +67,8 @@ class PLASMA_EXPORT Theme : public QObject
     // stylesheet
     Q_PROPERTY(QString styleSheet READ styleSheet NOTIFY themeChanged)
 
+    Q_PROPERTY(QPalette palette READ palette NOTIFY themeChanged)
+
 public:
     enum ColorRole {
         TextColor = 0, /**<  the text color to be used by items resting on the background */
@@ -215,6 +217,12 @@ public:
      */
     QString styleSheet(const QString &css = QString()) const;
 
+    /**
+     * Returns a QPalette with the colors set as defined by the theme.
+     * @since 5.68
+     */
+    QPalette palette() const;
+
     /**
      * This is an overloaded member provided to check with file timestamp
      * where cache is still valid.