fix: Respect dark mode using color roles for "2nd level list headings"

Hard coded color codes are replaced by Qt's color roles. This works in light and dark mode themes.

The term "2nd level list headings" refer to the snapshot timeline widget with headings like "Now" or "Yesterday" and to the "Shortcuts" list in the file list view with headings like "Global" and "Backup folders".

Fix #1601

CHANGES

@@ -1,6 +1,7 @@
 Back In Time
 
 Version 1.4.4-dev (development of upcoming release)
+* Fix: Respect dark mode using color roles (#1601)
 * Dependency: Migration to PyQt6
 * Build: PyLint unit test is skipped if PyLint isn't installed, but will always run on TravisCI (#1634)
 * Feature: Support rsync '--one-file-system' in Expert Options (#1598)

FAQ.md

@@ -454,6 +454,15 @@ Otherwise, kill the process. After that look into the folder
 
 For more details see the developer documentation: [Usage of control files (locks, flocks, logs and others)](common/doc-dev/4_Control_files_usage_(locks_flocks_logs_and_others).md)
 
+### Switching to dark or light mode in the desktop environment is ignored by BIT
+After restart _Back In Time_ it should addapt to the desktops current used
+color theme.
+
+It happens because Qt does not detect theme modifications out of the
+box. [Workarounds are known](https://stackoverflow.com/q/75457687), but
+generate a relatively large amount of code and in our opinion are not worth
+the effort.
+
 ## Error Handling
 
 ### What happens if I hibernate the computer while a backup is running?

qt/app.py

@@ -51,6 +51,7 @@
 from PyQt6.QtGui import (QAction,
                          QShortcut,
                          QDesktopServices,
+                         QPalette,
                          QColor,
                          QIcon,
                          QFileSystemModel)
@@ -1058,6 +1059,10 @@ def placesChanged(self, item, previous):
         self.updateFilesView(3)
 
     def addPlace(self, name, path, icon):
+        """
+        Dev note (buhtz, 2024-01-14): Parts of that code are redundant with
+        qttools.py::HeaderItem.__init__().
+        """
         item = QTreeWidgetItem()
 
         item.setText(0, name)
@@ -1069,9 +1074,13 @@ def addPlace(self, name, path, icon):
 
         if not path:
             item.setFont(0, qttools.fontBold(item.font(0)))
-            item.setFlags(Qt.ItemFlag.ItemIsEnabled)
-            item.setBackground(0, QColor(196, 196, 196))
-            item.setForeground(0, QColor(60, 60, 60))
+
+            # item.setFlags(Qt.ItemFlag.ItemIsEnabled)
+            item.setFlags(Qt.ItemFlag.NoItemFlags)
+            item.setForeground(
+                0, self.palette().color(QPalette.ColorRole.PlaceholderText))
+            item.setBackground(
+                0, self.palette().color(QPalette.ColorRole.Window))
 
         self.places.addTopLevelItem(item)
 
@@ -1088,6 +1097,7 @@ def updatePlaces(self):
 
         # add backup folders
         include_folders = self.config.include()
+
         if include_folders:
             folders = []
             for item in include_folders:

qt/qttools.py

@@ -31,14 +31,14 @@
 import os
 import sys
 
-from PyQt6.QtGui import (QAction, QFont, QColor, QIcon)
+from PyQt6.QtGui import (QAction, QFont, QPalette, QIcon)
 from PyQt6.QtCore import (QDir, Qt, pyqtSlot, pyqtSignal, QModelIndex,
                           QTranslator, QLocale, QLibraryInfo,
                           QT_VERSION_STR)
 from PyQt6.QtWidgets import (QFileDialog, QAbstractItemView, QListView,
                              QTreeView, QDialog, QApplication, QStyleFactory,
                              QTreeWidget, QTreeWidgetItem, QComboBox,
-                             QSystemTrayIcon, QWidget)
+                             QSystemTrayIcon)
 from datetime import (datetime, date, timedelta)
 from calendar import monthrange
 from packaging.version import Version
@@ -560,11 +560,20 @@ def updateText(self):
 
 class HeaderItem(TimeLineItem):
     def __init__(self, name, sid):
+        """
+        Dev note (buhtz, 2024-01-14): Parts of that code are redundant with
+        app.py::MainWindow.addPlace().
+        """
         super(HeaderItem, self).__init__()
         self.setText(0, name)
         self.setFont(0, fontBold(self.font(0)))
-        self.setBackground(0, QColor(196, 196, 196))
-        self.setForeground(0, QColor(60, 60, 60))
+
+        palette = QApplication.instance().palette()
+        self.setForeground(
+            0, palette.color(QPalette.ColorRole.PlaceholderText))
+        self.setBackground(
+            0, palette.color(QPalette.ColorRole.Window))
+
         self.setFlags(Qt.ItemFlag.NoItemFlags)
 
         self.setData(0, Qt.ItemDataRole.UserRole, sid)