main: Warn if -installsettings points to a path without settings

Especially confusing is that the "QtProject" part must be omitted, so
include that information in the warning.

Change-Id: I4214502fd045b0e13a55c50fa036194dec6dab35
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: hjk <hjk@qt.io>

src/app/main.cpp

@@ -614,6 +614,15 @@ int main(int argc, char **argv)
                                  QSettings::SystemScope,
                                  QLatin1String(Core::Constants::IDE_SETTINGSVARIANT_STR),
                                  QLatin1String(Core::Constants::IDE_CASED_ID));
+    // warn if -installsettings points to a place where no install settings are located
+    if (!options.installSettingsPath.isEmpty() && !QFileInfo::exists(installSettings->fileName())) {
+        displayError(QLatin1String("The install settings \"%1\" do not exist. The %2 option must "
+                                   "point to a path with existing settings, excluding the %3 part "
+                                   "of the path.")
+                         .arg(QDir::toNativeSeparators(installSettings->fileName()),
+                              INSTALL_SETTINGS_OPTION,
+                              Core::Constants::IDE_SETTINGSVARIANT_STR));
+    }
     Utils::TerminalCommand::setSettings(settings);
     setPixmapCacheLimit();
     loadFonts();