Make the default icon theme finding more elaborated

platformthemeplugin/hintsettings.cpp

@@ -18,6 +18,7 @@
 #include <QDBusArgument>
 #include <QDBusConnection>
 #include <QDBusInterface>
+#include <QDirIterator>
 
 static const QByteArray s_systemFontName = QByteArrayLiteral("Font");
 static const QByteArray s_systemFixedFontName = QByteArrayLiteral("FixedFont");
@@ -40,14 +41,21 @@ QString resolveSymlink(const QString &path) {
     return path;
 }
 
+// The default icon theme can be set by the user, e.g.,
+// sudo ln -sf /usr/local/share/icons/elementary-xfce /usr/local/share/icons/default
+// or
+// sudo ln -sf /usr/share/icons/elementary-xfce /usr/share/icons/default
+//
+// The XDG icon spec is overly complex and provides no clear way how to find the icon theme
+// based on the Name= entry. For example, on Ubuntu, the icon theme for KDE is called "Breeze" in index.theme,
+// but the folder is called "breeze".
+// So we need to read the icon.theme in each subdirectory of iconThemePath and compare the Name= entry with the themeNameFromFile.
+// If it matches, we have found the icon theme. The spec is way too complicated, resulting in precious cycles being
+// wasted every time an application starts up and the platform theme is loaded.
 HintsSettings::HintsSettings(QObject *parent)
     : QObject(parent),
       m_settings(new QSettings(QSettings::UserScope, "panda", "theme"))
 {
-    // The default icon theme can be set by the user, e.g.,
-    // sudo ln -sf /usr/local/share/icons/elementary-xfce /usr/local/share/icons/default
-    // or
-    // sudo ln -sf /usr/share/icons/elementary-xfce /usr/share/icons/default
 
     const QStringList iconThemePaths = xdgIconThemePaths();
 
@@ -75,7 +83,34 @@ HintsSettings::HintsSettings(QObject *parent)
                     if (line.startsWith("Name=")) {
                         qDebug() << "line" << line;
                         QString themeNameFromFile = line.mid(5);  // Remove "Name="
-                        defaultIconTheme = themeNameFromFile;
+                        QDir themesDir(resolveSymlink(iconThemePath));
+                        QDirIterator it(themesDir.path(), QDir::Dirs | QDir::NoDotAndDotDot, QDirIterator::NoIteratorFlags);
+                        while (it.hasNext()) {
+                            QString subDir = it.next();
+                            qDebug() << "subDir" << subDir;
+                            QFile subIndexThemeFile(resolveSymlink(subDir + "/index.theme"));
+                            if (subIndexThemeFile.exists()) {
+                                qDebug() << "subIndexThemeFile" << subIndexThemeFile.fileName();
+                                QFile subFile(subIndexThemeFile.fileName());
+                                if (subFile.open(QIODevice::ReadOnly | QIODevice::Text)) {
+                                    QTextStream subIn(&subFile);
+                                    while (!subIn.atEnd()) {
+                                        QString subLine = subIn.readLine();
+                                        if (subLine.startsWith("Name=")) {
+                                            qDebug() << "Comparing to" << subLine;
+                                            QString themeNameFromSubFile = subLine.mid(5);  // Remove "Name="
+                                            if (themeNameFromFile == themeNameFromSubFile) {
+                                                qDebug() << "Found default icon theme" << themeNameFromFile << "in" << subDir;
+                                                defaultIconTheme = themeNameFromSubFile;
+                                                break;
+                                            }
+                                        }
+                                    }
+                                }
+                            } else {
+                                qDebug() << "subIndexThemeFile" << subIndexThemeFile.fileName() << "does not exist";
+                            }
+                        }
                     }
                 }
             }