Show supported backends in --help output (#16441)

src/main.cpp

@@ -2,6 +2,9 @@
 // SPDX-License-Identifier: LGPL-2.1-or-later
 // Copyright (C) 2010-2013 celeron55, Perttu Ahola <celeron55@gmail.com>
 
+#include <map>
+#include <algorithm>
+
 #include "irrlichttypes_bloated.h"
 #include "irrlicht.h" // createDevice
 #include "irrlicht_changes/printing.h"
@@ -405,6 +408,22 @@ static void print_help(const OptionList &allowed_options)
 {
 	std::cout << _("Allowed options:") << std::endl;
 	print_allowed_options(allowed_options);
+	std::cout << std::endl;
+
+	std::pair<const char*, std::vector<std::string>> the_list[] = {
+		{"map", ServerMap::getDatabaseBackends()},
+		{"players", ServerEnvironment::getPlayerDatabaseBackends()},
+		{"auth", ServerEnvironment::getAuthDatabaseBackends()},
+		{"mod storage", Server::getModStorageDatabaseBackends()},
+	};
+
+	std::cout << "Supported database backends:";
+	for (auto &e : the_list) {
+		SORT_AND_UNIQUE(e.second);
+		std::cout << "\n  " << padStringRight(e.first, 16)
+			<< ": " << str_join(e.second, ", ");
+	}
+	std::cout << std::endl;
 }
 
 static void print_allowed_options(const OptionList &allowed_options)

src/server.cpp

@@ -4289,15 +4289,28 @@ ModStorageDatabase *Server::openModStorageDatabase(const std::string &world_path
 
 	std::string backend = world_mt.exists("mod_storage_backend") ?
 		world_mt.get("mod_storage_backend") : "files";
-	if (backend == "files")
+	if (backend == "files") {
 		warningstream << "/!\\ You are using the old mod storage files backend. "
-			<< "This backend is deprecated and may be removed in a future release /!\\"
-			<< std::endl << "Switching to SQLite3 is advised, "
-			<< "please read https://docs.luanti.org/for-server-hosts/database-backends." << std::endl;
+			"This backend is deprecated and may be removed in a future release /!\\"
+			"\nSwitching to SQLite3 is advised, "
+			"please read https://docs.luanti.org/for-server-hosts/database-backends." << std::endl;
+	}
 
 	return openModStorageDatabase(backend, world_path, world_mt);
 }
 
+std::vector<std::string> Server::getModStorageDatabaseBackends()
+{
+	std::vector<std::string> ret;
+	ret.emplace_back("sqlite3");
+#if USE_POSTGRESQL
+	ret.emplace_back("postgresql");
+#endif
+	ret.emplace_back("files");
+	ret.emplace_back("dummy");
+	return ret;
+}
+
 ModStorageDatabase *Server::openModStorageDatabase(const std::string &backend,
 		const std::string &world_path, const Settings &world_mt)
 {

src/server.h

@@ -435,6 +435,8 @@ public:
 	// map key = binary sha1, map value = file path
 	std::unordered_map<std::string, std::string> getMediaList();
 
+	static std::vector<std::string> getModStorageDatabaseBackends();
+
 	static ModStorageDatabase *openModStorageDatabase(const std::string &world_path);
 
 	static ModStorageDatabase *openModStorageDatabase(const std::string &backend,

src/serverenvironment.cpp

@@ -1828,6 +1828,21 @@ void ServerEnvironment::processActiveObjectRemove(ServerActiveObject *obj)
 	m_script->removeObjectReference(obj);
 }
 
+std::vector<std::string> ServerEnvironment::getPlayerDatabaseBackends()
+{
+	std::vector<std::string> ret;
+	ret.emplace_back("sqlite3");
+	ret.emplace_back("dummy");
+#if USE_POSTGRESQL
+	ret.emplace_back("postgresql");
+#endif
+#if USE_LEVELDB
+	ret.emplace_back("leveldb");
+#endif
+	ret.emplace_back("files");
+	return ret;
+}
+
 PlayerDatabase *ServerEnvironment::openPlayerDatabase(const std::string &name,
 		const std::string &savedir, const Settings &conf)
 {
@@ -1944,6 +1959,21 @@ bool ServerEnvironment::migratePlayersDatabase(const GameParams &game_params,
 	return true;
 }
 
+std::vector<std::string> ServerEnvironment::getAuthDatabaseBackends()
+{
+	std::vector<std::string> ret;
+	ret.emplace_back("sqlite3");
+	ret.emplace_back("dummy");
+#if USE_POSTGRESQL
+	ret.emplace_back("postgresql");
+#endif
+	ret.emplace_back("files");
+#if USE_LEVELDB
+	ret.emplace_back("leveldb");
+#endif
+	return ret;
+}
+
 AuthDatabase *ServerEnvironment::openAuthDatabase(
 		const std::string &name, const std::string &savedir, const Settings &conf)
 {

src/serverenvironment.h

@@ -278,12 +278,15 @@ public:
 	const std::vector<RemotePlayer *> getPlayers() const { return m_players; }
 	u32 getPlayerCount() const { return m_players.size(); }
 
+	static std::vector<std::string> getPlayerDatabaseBackends();
 	static bool migratePlayersDatabase(const GameParams &game_params,
 			const Settings &cmd_args);
 
 	AuthDatabase *getAuthDatabase() { return m_auth_database; }
+	static std::vector<std::string> getAuthDatabaseBackends();
 	static bool migrateAuthDatabase(const GameParams &game_params,
 			const Settings &cmd_args);
+
 private:
 
 	/**

src/servermap.cpp

@@ -2,6 +2,8 @@
 // SPDX-License-Identifier: LGPL-2.1-or-later
 // Copyright (C) 2010-2024 celeron55, Perttu Ahola <celeron55@gmail.com>
 
+#include <algorithm>
+
 #include "map.h"
 #include "mapsector.h"
 #include "filesys.h"
@@ -568,36 +570,62 @@ void ServerMap::listAllLoadedBlocks(std::vector<v3s16> &dst)
 	}
 }
 
+std::vector<std::string> ServerMap::getDatabaseBackends()
+{
+	std::vector<std::string> ret;
+	ret.emplace_back("sqlite3");
+	ret.emplace_back("dummy");
+#if USE_LEVELDB
+	ret.emplace_back("leveldb");
+#endif
+#if USE_REDIS
+	ret.emplace_back("redis");
+#endif
+#if USE_POSTGRESQL
+	ret.emplace_back("postgresql");
+#endif
+	return ret;
+}
+
 MapDatabase *ServerMap::createDatabase(
 	const std::string &name,
 	const std::string &savedir,
 	Settings &conf)
 {
+	// Hopefully this way we don't forget to keep them in sync.
+	auto valid = getDatabaseBackends();
+	if (!CONTAINS(valid, name)) {
+		auto err = std::string("Database backend \"") + name + "\" unknown or not supported";
+		errorstream << err << std::endl;
+		throw BaseException(err);
+	}
+
 	MapDatabase *db = nullptr;
-	verbosestream << "Creating map database with backend \"" << name << "\"" << std::endl;
+	infostream << "Creating map database with backend \"" << name << "\"" << std::endl;
 
 	if (name == "sqlite3")
 		db = new MapDatabaseSQLite3(savedir);
-	if (name == "dummy")
+	else if (name == "dummy")
 		db = new Database_Dummy();
-	#if USE_LEVELDB
-	if (name == "leveldb")
+#if USE_LEVELDB
+	else if (name == "leveldb")
 		db = new Database_LevelDB(savedir);
-	#endif
-	#if USE_REDIS
-	if (name == "redis")
+#endif
+#if USE_REDIS
+	else if (name == "redis")
 		db = new Database_Redis(conf);
-	#endif
-	#if USE_POSTGRESQL
-	if (name == "postgresql") {
+#endif
+#if USE_POSTGRESQL
+	else if (name == "postgresql") {
 		std::string connect_string;
 		conf.getNoEx("pgsql_connection", connect_string);
 		db = new MapDatabasePostgreSQL(connect_string);
 	}
-	#endif
+#endif
+
+	// Constructor can't return null, only throw
+	sanity_check(db);
 
-	if (!db)
-		throw BaseException(std::string("Database backend ") + name + " not supported.");
 	// Do this to get feedback about errors asap
 	db->verifyDatabase();
 	assert(db->initialized());

src/servermap.h

@@ -101,6 +101,7 @@ public:
 	/*
 		Database functions
 	*/
+	static std::vector<std::string> getDatabaseBackends();
 	static MapDatabase *createDatabase(const std::string &name, const std::string &savedir, Settings &conf);
 
 	// Call these before and after saving of blocks