Rewrite the correct databases value when dbnum is clamped to 1 in cluster mode

src/config.c

@@ -609,6 +609,7 @@ void loadServerConfigFromString(char *config) {
     }
 
     /* in case cluster mode is enabled dbnum must be 1 */
+    server.dbnum = server.config_dbnum;
     if (server.cluster_enabled && server.dbnum > 1) {
         serverLog(LL_WARNING, "WARNING: Changing databases number from %d to 1 since we are in cluster mode",
                   server.dbnum);
@@ -3252,7 +3253,7 @@ standardConfig static_configs[] = {
     createEnumConfig("rdb-version-check", NULL, MODIFIABLE_CONFIG, rdb_version_check_enum, server.rdb_version_check, RDB_VERSION_CHECK_STRICT, NULL, NULL),
 
     /* Integer configs */
-    createIntConfig("databases", NULL, IMMUTABLE_CONFIG, 1, INT_MAX, server.dbnum, 16, INTEGER_CONFIG, NULL, NULL),
+    createIntConfig("databases", NULL, IMMUTABLE_CONFIG, 1, INT_MAX, server.config_dbnum, 16, INTEGER_CONFIG, NULL, NULL),
     createIntConfig("port", NULL, MODIFIABLE_CONFIG, 0, 65535, server.port, 6379, INTEGER_CONFIG, NULL, updatePort),                                   /* TCP port. */
     createIntConfig("io-threads", NULL, DEBUG_CONFIG | IMMUTABLE_CONFIG, 1, IO_THREADS_MAX_NUM, server.io_threads_num, 1, INTEGER_CONFIG, NULL, NULL), /* Single threaded by default */
     createIntConfig("events-per-io-thread", NULL, MODIFIABLE_CONFIG | HIDDEN_CONFIG, 0, INT_MAX, server.events_per_io_thread, 2, INTEGER_CONFIG, NULL, NULL),

src/server.h

@@ -1782,7 +1782,8 @@ struct valkeyServer {
     unsigned long active_defrag_max_scan_fields; /* maximum number of fields of set/hash/zset/list to process from
                                                     within the main dict scan */
     size_t client_max_querybuf_len;              /* Limit for client query buffer length */
-    int dbnum;                                   /* Total number of configured DBs */
+    int dbnum;                                   /* Total number of DBs */
+    int config_dbnum;                            /* Total number of configured DBs */
     int supervised;                              /* 1 if supervised, 0 otherwise. */
     int supervised_mode;                         /* See SUPERVISED_* */
     int daemonize;                               /* True if running as a daemon */

tests/unit/cluster/introspection.tcl

@@ -0,0 +1,8 @@
+start_cluster 1 0 {tags {external:skip cluster}} {
+    test "CONFIG REWRITE databases" {
+        assert_equal 16 [lindex [r config get databases] 1]
+        r config rewrite
+        restart_server 0 true false
+        assert_equal 16 [lindex [r config get databases] 1]
+    }
+}