macOS: By default use dark theme in system dark mode

Like already done for Windows.

Change-Id: I7919ecb92da5d4baeedf2068f09c341d39728ecc
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/libs/utils/theme/theme.cpp

@@ -79,6 +79,16 @@ static void maybeForceMacOSLight(Theme *theme)
 #endif
 }
 
+static bool macOSSystemIsDark()
+{
+#ifdef Q_OS_MACOS
+    static bool systemIsDark = Internal::currentAppearanceIsDark();
+    return systemIsDark;
+#else
+    return false;
+#endif
+}
+
 void setCreatorTheme(Theme *theme)
 {
     if (m_creatorTheme == theme)
@@ -257,6 +267,8 @@ bool Theme::systemUsesDarkMode()
         bool ok;
         const auto setting = QSettings(regkey, QSettings::NativeFormat).value("AppsUseLightTheme").toInt(&ok);
         return ok && setting == 0;
+    } else if (HostOsInfo::isMacHost()) {
+        return macOSSystemIsDark();
     }
     return false;
 }
@@ -278,6 +290,7 @@ static QPalette copyPalette(const QPalette &p)
 
 void Theme::setInitialPalette(Theme *initTheme)
 {
+    macOSSystemIsDark(); // initialize value for system mode
     maybeForceMacOSLight(initTheme);
     initialPalette();
 }

src/libs/utils/theme/theme_mac.h

@@ -29,6 +29,7 @@ namespace Utils {
 namespace Internal {
 
 void forceMacOSLightAquaApperance();
+bool currentAppearanceIsDark();
 
 } // Internal
 } // Utils

src/libs/utils/theme/theme_mac.mm

@@ -49,5 +49,17 @@ void forceMacOSLightAquaApperance()
         NSApp.appearance = [NSAppearance appearanceNamed:NSAppearanceNameAqua];
 }
 
+bool currentAppearanceIsDark()
+{
+#if __has_builtin(__builtin_available)
+    if (__builtin_available(macOS 10.14, *)) {
+        auto appearance = [NSApp.effectiveAppearance
+            bestMatchFromAppearancesWithNames:@[NSAppearanceNameAqua, NSAppearanceNameDarkAqua]];
+        return [appearance isEqualToString:NSAppearanceNameDarkAqua];
+    }
+#endif
+    return false;
+}
+
 } // Internal
 } // Utils