[Server] Add per-run configuration overrides (#7820)

Add --set key=value to override a section-qualified scalar configuration key for a single run and --print-config to print the effective configuration, with secrets redacted. SettingsCache owns the override map, so reads see the override without rewriting the ini file, and rebuilds the disallowed-name regexps when users/disallowedregexp is overridden. Bare keys and array-scoped keys are rejected because array loops read them relative to the active group, where a full-key override would either be ignored or rewrite every entry.

Cover the ini, default, override, override-only-key, regexp-rebuild, secret-redaction, and parse paths with a server-labelled gtest.

servatrice/src/settingscache.cpp

@@ -18,6 +18,78 @@ SettingsCache::SettingsCache(const QString &fileName, QSettings::Format format,
     // first, figure out if we are running in portable mode
     isPortableBuild = QFile::exists(qApp->applicationDirPath() + "/portable.dat");
 
+    rebuildDisallowedRegExps();
+}
+
+QVariant SettingsCache::value(const QString &key, const QVariant &defaultValue) const
+{
+    const auto it = overrides.constFind(key);
+    if (it != overrides.constEnd()) {
+        return it.value();
+    }
+    return QSettings::value(key, defaultValue);
+}
+
+void SettingsCache::setOverride(const QString &key, const QVariant &value)
+{
+    overrides.insert(key, value);
+}
+
+bool SettingsCache::parseOverride(const QString &entry, QString &key, QVariant &value)
+{
+    const int separator = entry.indexOf('=');
+    if (separator <= 0) {
+        return false;
+    }
+
+    const QString parsedKey = entry.left(separator).trimmed();
+    if (parsedKey.isEmpty() || !parsedKey.contains('/')) {
+        // A bare key is read relative to the active QSettings group by array
+        // loops, so one override could rewrite every room, channel, or game type.
+        return false;
+    }
+
+    const QStringList segments = parsedKey.split('/');
+    if (segments.last() == "size") {
+        return false;
+    }
+    for (const QString &segment : segments) {
+        bool isNumber = false;
+        segment.toInt(&isNumber);
+        if (isNumber) {
+            // Numeric segments identify array entries, which are read relative
+            // to the active array group and never match a full-key override.
+            return false;
+        }
+    }
+
+    key = parsedKey;
+    value = entry.mid(separator + 1);
+    return true;
+}
+
+bool SettingsCache::isSecretKey(const QString &key)
+{
+    const QString lower = key.toLower();
+    return lower.contains("password") || lower.contains("secret") || lower.contains("legacy_backup_key");
+}
+
+QStringList SettingsCache::effectiveKeys() const
+{
+    QStringList keys = allKeys();
+    for (auto it = overrides.constBegin(); it != overrides.constEnd(); ++it) {
+        if (!keys.contains(it.key())) {
+            keys.append(it.key());
+        }
+    }
+    keys.sort();
+    return keys;
+}
+
+void SettingsCache::rebuildDisallowedRegExps()
+{
+    disallowedRegExp.clear();
+
     QStringList disallowedRegExpStr = value("users/disallowedregexp", "").toString().split(",", Qt::SkipEmptyParts);
     disallowedRegExpStr.removeDuplicates();
     for (const QString &regExpStr : disallowedRegExpStr) {