Saveload: Table format sub-struct support

src/sl/bridge_signal_sl.cpp

@@ -18,7 +18,7 @@ static const NamedSaveLoad _long_bridge_signal_storage_desc[] = {
 
 static void Load_XBSS()
 {
-	std::vector<SaveLoad> slt = SlTableHeaderOrRiff(_long_bridge_signal_storage_desc);
+	SaveLoadTableData slt = SlTableHeaderOrRiff(_long_bridge_signal_storage_desc);
 
 	int index;
 	while ((index = SlIterateArray()) != -1) {
@@ -29,7 +29,7 @@ static void Load_XBSS()
 
 static void Save_XBSS()
 {
-	std::vector<SaveLoad> slt = SlTableHeader(_long_bridge_signal_storage_desc);
+	SaveLoadTableData slt = SlTableHeader(_long_bridge_signal_storage_desc);
 
 	for (auto &it : _long_bridge_signal_sim_map) {
 		LongBridgeSignalStorage &lbss = it.second;

src/sl/cargopacket_sl.cpp

@@ -181,7 +181,7 @@ NamedSaveLoadTable GetCargoPacketDesc()
  */
 static void Save_CAPA()
 {
-	std::vector<SaveLoad> slt = SlTableHeader(GetCargoPacketDesc());
+	SaveLoadTableData slt = SlTableHeader(GetCargoPacketDesc());
 
 	for (CargoPacket *cp : CargoPacket::Iterate()) {
 		SlSetArrayIndex(cp->index);
@@ -194,7 +194,7 @@ static void Save_CAPA()
  */
 static void Load_CAPA()
 {
-	std::vector<SaveLoad> slt = SlTableHeaderOrRiff(GetCargoPacketDesc());
+	SaveLoadTableData slt = SlTableHeaderOrRiff(GetCargoPacketDesc());
 
 	int index;
 	while ((index = SlIterateArray()) != -1) {

src/sl/cheat_sl.cpp

@@ -80,7 +80,7 @@ std::vector<NamedSaveLoad> GetCheatsDesc(bool save) {
  */
 static void Save_CHTS()
 {
-	std::vector<SaveLoad> slt = SlTableHeader(GetCheatsDesc(true));
+	SaveLoadTableData slt = SlTableHeader(GetCheatsDesc(true));
 
 	SlSetArrayIndex(0);
 	SlObjectSaveFiltered(&_cheats, slt);
@@ -105,7 +105,7 @@ static void Load_CHTS()
 		};
 
 		UnknownCheatHandler uch{};
-		std::vector<SaveLoad> slt = SlTableHeader(GetCheatsDesc(false), &uch);
+		SaveLoadTableData slt = SlTableHeader(GetCheatsDesc(false), &uch);
 
 		if (SlIterateArray() == -1) return;
 		SlObjectLoadFiltered(&_cheats, slt);
@@ -114,7 +114,7 @@ static void Load_CHTS()
 		}
 	} else {
 		size_t count = SlGetFieldLength();
-		std::vector<SaveLoad> slt = SlTableHeaderOrRiff(GetCheatsDesc(false));
+		SaveLoadTableData slt = SlTableHeaderOrRiff(GetCheatsDesc(false));
 
 		/* Cheats were added over the years without a savegame bump. They are
 		 * stored as 2 SLE_BOOLs per entry. "count" indicates how many SLE_BOOLs

src/sl/debug_sl.cpp

@@ -85,7 +85,7 @@ static void Load_DBGD()
 		NSLT("config", SLEG_SSTR(_loadgame_DBGC_data, SLE_STR | SLF_ALLOW_CONTROL | SLF_ALLOW_NEWLINE)),
 		NSLT("log",    SLEG_SSTR(_loadgame_DBGL_data, SLE_STR | SLF_ALLOW_CONTROL | SLF_ALLOW_NEWLINE)),
 	};
-	SlLoadTableOrRiffFiltered(nsl);
+	SlLoadTableObjectChunk(nsl);
 }
 
 static void Check_DBGD()
@@ -99,7 +99,7 @@ static void Check_DBGD()
 		NSLT("config", SLEG_SSTR(_load_check_data.debug_config_data, SLE_STR | SLF_ALLOW_CONTROL | SLF_ALLOW_NEWLINE)),
 		NSLT("log",    SLEG_SSTR(_load_check_data.debug_log_data, SLE_STR | SLF_ALLOW_CONTROL | SLF_ALLOW_NEWLINE)),
 	};
-	SlLoadTableOrRiffFiltered(nsl);
+	SlLoadTableObjectChunk(nsl);
 }
 
 extern const ChunkHandler debug_chunk_handlers[] = {

src/sl/industry_sl.cpp

@@ -167,7 +167,7 @@ static const NamedSaveLoad _industrytype_builder_desc[] = {
 /** Save industry-type build data. */
 static void Save_ITBL()
 {
-	std::vector<SaveLoad> sld = SlTableHeader(_industrytype_builder_desc);
+	SaveLoadTableData sld = SlTableHeader(_industrytype_builder_desc);
 
 	for (int i = 0; i < NUM_INDUSTRYTYPES; i++) {
 		SlSetArrayIndex(i);
@@ -178,7 +178,7 @@ static void Save_ITBL()
 /** Load industry-type build data. */
 static void Load_ITBL()
 {
-	std::vector<SaveLoad> sld = SlTableHeaderOrRiff(_industrytype_builder_desc);
+	SaveLoadTableData sld = SlTableHeaderOrRiff(_industrytype_builder_desc);
 
 	for (IndustryType it = 0; it < NUM_INDUSTRYTYPES; it++) {
 		_industry_builder.builddata[it].Reset();

src/sl/newgrf_sl.cpp

@@ -36,7 +36,7 @@ static const NamedSaveLoad _newgrf_mapping_desc_new[] = {
  */
 void Save_NewGRFMapping(const OverrideManagerBase &mapping)
 {
-	std::vector<SaveLoad> sld = SlTableHeader(_newgrf_mapping_desc_new);
+	SaveLoadTableData sld = SlTableHeader(_newgrf_mapping_desc_new);
 
 	for (uint i = 0; i < mapping.GetMaxMapping(); i++) {
 		if (mapping.mappings[i].grfid == 0 &&
@@ -60,7 +60,7 @@ void Load_NewGRFMapping(OverrideManagerBase &mapping)
 	uint max_id = mapping.GetMaxMapping();
 
 	SaveLoadTable slt;
-	std::vector<SaveLoad> sld;
+	SaveLoadTableData sld;
 
 	if (SlXvIsFeaturePresent(XSLFI_NEWGRF_ENTITY_EXTRA) || SlIsTableChunk()) {
 		sld = SlTableHeaderOrRiff(_newgrf_mapping_desc_new);
@@ -91,7 +91,7 @@ static const NamedSaveLoad _grfconfig_desc[] = {
 
 static void Save_NGRF()
 {
-	std::vector<SaveLoad> sld = SlTableHeader(_grfconfig_desc);
+	SaveLoadTableData sld = SlTableHeader(_grfconfig_desc);
 	int index = 0;
 
 	for (GRFConfig *c = _grfconfig; c != nullptr; c = c->next) {
@@ -108,7 +108,7 @@ static void Load_NGRF_common(GRFConfig *&grfconfig)
 	if (SlXvIsFeaturePresent(XSLFI_TABLE_NEWGRF_SL, 1, 1)) {
 		SlLoadTableWithArrayLengthPrefixesMissing();
 	}
-	std::vector<SaveLoad> sld = SlTableHeaderOrRiff(_grfconfig_desc);
+	SaveLoadTableData sld = SlTableHeaderOrRiff(_grfconfig_desc);
 	ClearGRFConfigList(&grfconfig);
 	while (SlIterateArray() != -1) {
 		GRFConfig *c = new GRFConfig();

src/sl/newsignals_sl.cpp

@@ -21,7 +21,7 @@ static const NamedSaveLoad _new_signal_style_mapping_desc[] = {
 
 static void Save_NSID()
 {
-	std::vector<SaveLoad> slt = SlTableHeader(_new_signal_style_mapping_desc);
+	SaveLoadTableData slt = SlTableHeader(_new_signal_style_mapping_desc);
 
 	int index = 0;
 	for (NewSignalStyleMapping &it : _new_signal_style_mapping) {
@@ -35,7 +35,7 @@ static void Load_NSID()
 	_new_signal_style_mapping.fill({});
 
 	if (SlIsTableChunk()) {
-		std::vector<SaveLoad> slt = SlTableHeader(_new_signal_style_mapping_desc);
+		SaveLoadTableData slt = SlTableHeader(_new_signal_style_mapping_desc);
 
 		int index;
 		while ((index = SlIterateArray()) != -1) {

src/sl/saveload.cpp

@@ -230,6 +230,19 @@ size_t MemoryDumper::GetSize() const
 	return this->completed_block_bytes + (this->bufe ? (MEMORY_CHUNK_SIZE - (this->bufe - this->buf)) : 0);
 }
 
+/**
+ * Get the size of the memory dump made so far.
+ * @return The size.
+ */
+size_t MemoryDumper::GetWriteOffsetGeneric() const
+{
+	if (this->saved_buf != nullptr) {
+		return this->buf - this->autolen_buf;
+	} else {
+		return this->GetSize();
+	}
+}
+
 enum SaveLoadBlockFlags {
 	SLBF_TABLE_ARRAY_LENGTH_PREFIX_MISSING, ///< Table chunk arrays were incorrectly saved without the length prefix, skip reading the length prefix on load
 };
@@ -1886,6 +1899,11 @@ size_t SlCalcObjMemberLength(const void *object, const SaveLoad &sld)
 		case SL_WRITEBYTE: return 1; // a uint8_t is logically of size 1
 		case SL_VEH_INCLUDE: return SlCalcObjLength(object, GetVehicleDescription(VEH_END));
 		case SL_ST_INCLUDE: return SlCalcObjLength(object, GetBaseStationDescription());
+
+		case SL_STRUCT:
+		case SL_STRUCTLIST:
+			NOT_REACHED(); // SlAutolength or similar should be used for sub-structs
+
 		default: NOT_REACHED();
 	}
 	return 0;
@@ -1906,6 +1924,8 @@ static void SlFilterObjectMember(const SaveLoad &sld, std::vector<SaveLoad> &sav
 		case SL_RING:
 		case SL_STDSTR:
 		case SL_VARVEC:
+		case SL_STRUCT:
+		case SL_STRUCTLIST:
 			/* CONDITIONAL saveload types depend on the savegame version */
 			if (!SlIsObjectValidInSavegame(sld)) return;
 
@@ -1921,6 +1941,8 @@ static void SlFilterObjectMember(const SaveLoad &sld, std::vector<SaveLoad> &sav
 						case SL_REFLIST:
 						case SL_PTRRING:
 						case SL_VEC:
+						case SL_STRUCT:
+						case SL_STRUCTLIST:
 							break;
 
 						/* non-ptr types do not require SLA_PTRS or SLA_NULL actions */
@@ -2032,6 +2054,51 @@ bool SlObjectMemberGeneric(void *object, const SaveLoad &sld)
 			}
 			break;
 
+		case SL_STRUCT:
+		case SL_STRUCTLIST:
+			switch (action) {
+				case SLA_SAVE: {
+					if (sld.cmd == SL_STRUCT) {
+						/* Number of structs written in the savegame: write a value of 1, change to zero later if nothing after this was written */
+						_sl.dumper->WriteByte(1);
+						size_t offset = _sl.dumper->GetWriteOffsetGeneric();
+						sld.struct_handler->Save(object);
+						if (offset == _sl.dumper->GetWriteOffsetGeneric()) {
+							/* Nothing was actaully written, so it's safe to change the 1 above to 0 */
+							_sl.dumper->UnWriteByte(); // This is fine iff nothing has been written since the WriteByte(1)
+							_sl.dumper->RawWriteByte(0);
+						}
+					} else {
+						sld.struct_handler->Save(object);
+					}
+					break;
+				}
+
+				case SLA_LOAD_CHECK: {
+					if (sld.cmd == SL_STRUCT && SlIsTableChunk()) {
+						if (SlGetStructListLength(1) == 0) break;
+					}
+					sld.struct_handler->LoadCheck(object);
+					break;
+				}
+
+				case SLA_LOAD: {
+					if (sld.cmd == SL_STRUCT && SlIsTableChunk()) {
+						if (SlGetStructListLength(1) == 0) break;
+					}
+					sld.struct_handler->Load(object);
+					break;
+				}
+
+				case SLA_PTRS:
+					sld.struct_handler->FixPointers(object);
+					break;
+
+				case SLA_NULL: break;
+				default: NOT_REACHED();
+			}
+			break;
+
 		/* SL_WRITEBYTE writes a value to the savegame to identify the type of an object.
 		 * When loading, the value is read explicitly with SlReadByte() to determine which
 		 * object description to use. */
@@ -2141,34 +2208,18 @@ bool SlIsTableChunk()
 
 void SlSkipTableHeader()
 {
+	uint sub_tables = 0;
 	while (true) {
 		uint8_t type = SlReadByte();
 		if (type == SLE_FILE_END) break;
 
+		if ((type & SLE_FILE_TYPE_MASK) == SLE_FILE_STRUCT) sub_tables++;
+
 		SlString(nullptr, 0, SLE_FILE_STRING | SLE_VAR_NULL);
 	}
-}
+	for (uint i = 0; i < sub_tables; i++) {
-
+		SlSkipTableHeader();
-/**
- * Calculate the size of the table header.
- * @param slt The SaveLoad table with objects to save/load.
- * @return size of given object.
- */
-static size_t SlCalcTableHeader(const NamedSaveLoadTable &slt)
-{
-	size_t length = 0;
-
-	for (auto &nsld : slt) {
-		if (StrEmpty(nsld.name) || !SlIsObjectValidInSavegame(nsld.save_load)) continue;
-
-		length += 1 + SlCalcStringLen(&nsld.name, 0, SLE_STR);
 	}
-
-	length++; // End-of-list entry.
-
-	/* SL_STRUCTLIST, SL_STRUCT not currently implemented */
-
-	return length;
 }
 
 /**
@@ -2198,22 +2249,55 @@ static uint8_t GetSavegameTableFileType(const SaveLoad &sld)
 		case SL_WRITEBYTE:
 			return SLE_FILE_U8;
 
+		case SL_STRUCT:
+		case SL_STRUCTLIST:
+			return SLE_FILE_STRUCT | SLE_FILE_HAS_LENGTH_FIELD;
+
 		default: NOT_REACHED();
 	}
 }
 
+/**
+ * Handler that is assigned when there is a struct read in the savegame which
+ * is not known to the code. This means we are going to skip it.
+ */
+class SaveLoadSkipStructHandler : public SaveLoadStructHandler {
+	void Save(void *) const override
+	{
+		NOT_REACHED();
+	}
+
+	void Load(void *object) const override
+	{
+		size_t length = SlGetStructListLength(UINT32_MAX);
+		for (; length > 0; length--) {
+			SlObjectLoadFiltered(object, this->GetLoadDescription());
+		}
+	}
+
+	void LoadCheck(void *object) const override
+	{
+		this->Load(object);
+	}
+
+	NamedSaveLoadTable GetDescription() const override
+	{
+		return {};
+	}
+};
+
 /**
  * Save or Load a table header.
  * @note a table-header can never contain more than 65535 fields.
  * @param slt The NamedSaveLoad table with objects to save/load.
  * @return The ordered SaveLoad array to use.
  */
-std::vector<SaveLoad> SlTableHeader(const NamedSaveLoadTable &slt, TableHeaderSpecialHandler *special_handler)
+SaveLoadTableData SlTableHeader(const NamedSaveLoadTable &slt, TableHeaderSpecialHandler *special_handler)
 {
 	/* You can only use SlTableHeader if you are a CH_TABLE. */
 	assert(_sl.block_mode == CH_TABLE || _sl.block_mode == CH_SPARSE_TABLE);
 
-	std::vector<SaveLoad> saveloads;
+	SaveLoadTableData saveloads;
 
 	switch (_sl.action) {
 		case SLA_LOAD_CHECK:
@@ -2261,15 +2345,20 @@ std::vector<SaveLoad> SlTableHeader(const NamedSaveLoadTable &slt, TableHeaderSp
 					DEBUG(sl, _sl.action == SLA_LOAD ? 2 : 6, "Field '%s' of type 0x%02X not found, skipping", key.c_str(), type);
 
 					SaveLoadType saveload_type;
+					SaveLoadStructHandler *struct_handler = nullptr;
 					switch (type & SLE_FILE_TYPE_MASK) {
 						case SLE_FILE_STRING:
 							/* Strings are always marked with SLE_FILE_HAS_LENGTH_FIELD, as they are a list of chars. */
 							saveload_type = SL_STDSTR;
 							break;
 
-						case SLE_FILE_STRUCT:
+						case SLE_FILE_STRUCT: {
-							SlErrorCorrupt("SLE_FILE_STRUCT not supported yet");
+							saveload_type = SL_STRUCTLIST;
+							auto handler = std::make_unique<SaveLoadSkipStructHandler>();
+							struct_handler = handler.get();
+							saveloads.struct_handlers.push_back(std::move(handler));
 							break;
+						}
 
 						default:
 							saveload_type = (type & SLE_FILE_HAS_LENGTH_FIELD) ? SL_ARR : SL_VAR;
@@ -2277,7 +2366,7 @@ std::vector<SaveLoad> SlTableHeader(const NamedSaveLoadTable &slt, TableHeaderSp
 					}
 
 					/* We don't know this field, so read to nothing. */
-					saveloads.push_back({ true, saveload_type, ((VarType)type & SLE_FILE_TYPE_MASK) | SLE_VAR_NULL, 1, SL_MIN_VERSION, SL_MAX_VERSION, SLTAG_TABLE_UNKNOWN, nullptr, SlXvFeatureTest() });
+					saveloads.push_back({ true, saveload_type, ((VarType)type & SLE_FILE_TYPE_MASK) | SLE_VAR_NULL, 1, SL_MIN_VERSION, SL_MAX_VERSION, SLTAG_TABLE_UNKNOWN, nullptr, SlXvFeatureTest(), struct_handler });
 					continue;
 				}
 
@@ -2292,17 +2381,28 @@ std::vector<SaveLoad> SlTableHeader(const NamedSaveLoadTable &slt, TableHeaderSp
 					SlErrorCorrupt("Field type is different than expected");
 				}
 				saveloads.push_back(*sld_it->save_load);
+
+				if ((type & SLE_FILE_TYPE_MASK) == SLE_FILE_STRUCT) {
+					std::unique_ptr<SaveLoadStructHandler> handler = saveloads.back().struct_handler_factory();
+					saveloads.back().struct_handler = handler.get();
+					saveloads.struct_handlers.push_back(std::move(handler));
+				}
 			}
 
-			/* SL_STRUCTLIST, SL_STRUCT not currently implemented */
+			for (auto &sld : saveloads) {
+				if (sld.cmd == SL_STRUCTLIST || sld.cmd == SL_STRUCT) {
+					sld.struct_handler->table_data = SlTableHeader(sld.struct_handler->GetDescription());
+				}
+			}
 
 			break;
 		}
 
 		case SLA_SAVE: {
-			/* Automatically calculate the length? */
+			const NeedLength orig_need_length = _sl.need_length;
-			if (_sl.need_length != NL_NONE) {
+			if (orig_need_length != NL_NONE) {
-				SlSetLength(SlCalcTableHeader(slt));
+				_sl.need_length = NL_NONE;
+				_sl.dumper->StartAutoLength();
 			}
 
 			for (auto &nsld : slt) {
@@ -2319,7 +2419,21 @@ std::vector<SaveLoad> SlTableHeader(const NamedSaveLoadTable &slt, TableHeaderSp
 			/* Add an end-of-header marker. */
 			SlWriteByte(SLE_FILE_END);
 
-			/* SL_STRUCTLIST, SL_STRUCT not currently implemented */
+			for (auto &sld : saveloads) {
+				if (sld.cmd == SL_STRUCTLIST || sld.cmd == SL_STRUCT) {
+					std::unique_ptr<SaveLoadStructHandler> handler = sld.struct_handler_factory();
+					sld.struct_handler = handler.get();
+					sld.struct_handler->table_data = SlTableHeader(sld.struct_handler->GetDescription());
+					saveloads.struct_handlers.push_back(std::move(handler));
+				}
+			}
+
+			if (orig_need_length != NL_NONE) {
+				auto result = _sl.dumper->StopAutoLength();
+				_sl.need_length = orig_need_length;
+				SlSetLength(result.size());
+				_sl.dumper->CopyBytes(result);
+			}
 
 			break;
 		}
@@ -2330,11 +2444,11 @@ std::vector<SaveLoad> SlTableHeader(const NamedSaveLoadTable &slt, TableHeaderSp
 	return saveloads;
 }
 
-std::vector<SaveLoad> SlTableHeaderOrRiff(const NamedSaveLoadTable &slt)
+SaveLoadTableData SlTableHeaderOrRiff(const NamedSaveLoadTable &slt)
 {
 	if (SlIsTableChunk()) return SlTableHeader(slt);
 
-	std::vector<SaveLoad> saveloads;
+	SaveLoadTableData saveloads;
 	for (auto &nsld : slt) {
 		if ((nsld.nsl_flags & NSLF_TABLE_ONLY) != 0) continue;
 		SlFilterObjectMember(nsld.save_load, saveloads);
@@ -2363,6 +2477,28 @@ void SlLoadTableWithArrayLengthPrefixesMissing()
 	SetBit(_sl.block_flags, SLBF_TABLE_ARRAY_LENGTH_PREFIX_MISSING);
 }
 
+/**
+ * Set the length of this list.
+ * @param The length of the list.
+ */
+void SlSetStructListLength(size_t length)
+{
+	SlWriteArrayLength(length);
+}
+
+/**
+ * Get the length of this list; if it exceeds the limit, error out.
+ * @param limit The maximum size the list can be.
+ * @return The length of the list.
+ */
+size_t SlGetStructListLength(size_t limit)
+{
+	size_t length = SlReadArrayLength();
+	if (length > limit) SlErrorCorrupt("List exceeds storage size");
+
+	return length;
+}
+
 void SlSkipChunkContents()
 {
 	if (SlIsTableChunk()) SlSkipTableHeader();

src/sl/saveload.h

@@ -1092,12 +1092,15 @@ struct TableHeaderSpecialHandler {
 
 bool SlIsTableChunk();
 void SlSkipTableHeader();
-std::vector<SaveLoad> SlTableHeader(const NamedSaveLoadTable &slt, TableHeaderSpecialHandler *special_handler = nullptr);
+SaveLoadTableData SlTableHeader(const NamedSaveLoadTable &slt, TableHeaderSpecialHandler *special_handler = nullptr);
-std::vector<SaveLoad> SlTableHeaderOrRiff(const NamedSaveLoadTable &slt);
+SaveLoadTableData SlTableHeaderOrRiff(const NamedSaveLoadTable &slt);
 void SlSaveTableObjectChunk(const SaveLoadTable &slt);
 void SlLoadTableOrRiffFiltered(const SaveLoadTable &slt);
 void SlLoadTableWithArrayLengthPrefixesMissing();
 
+void SlSetStructListLength(size_t length);
+size_t SlGetStructListLength(size_t limit);
+
 void SlSkipChunkContents();
 
 inline void SlSaveTableObjectChunk(const NamedSaveLoadTable &slt)
@@ -1105,6 +1108,16 @@ inline void SlSaveTableObjectChunk(const NamedSaveLoadTable &slt)
 	SlSaveTableObjectChunk(SlTableHeader(slt));
 }
 
+inline void SlLoadTableObjectChunk(const NamedSaveLoadTable &slt)
+{
+	SlLoadTableOrRiffFiltered(SlTableHeader(slt));
+}
+
+inline void SlLoadTableObjectChunk(const SaveLoadTable &slt)
+{
+	SlLoadTableOrRiffFiltered(slt);
+}
+
 inline void SlLoadTableOrRiffFiltered(const NamedSaveLoadTable &slt)
 {
 	SlLoadTableOrRiffFiltered(SlTableHeaderOrRiff(slt));

src/sl/saveload_buffer.h

@@ -256,6 +256,12 @@ struct MemoryDumper {
 		this->CopyBytes(buffer.data(), buffer.size());
 	}
 
+	/** For limited/special purposes only */
+	inline void UnWriteByte()
+	{
+		this->buf--;
+	}
+
 	inline void RawWriteByte(uint8_t b)
 	{
 		*this->buf++ = b;
@@ -331,6 +337,7 @@ struct MemoryDumper {
 
 	void Flush(SaveFilter &writer);
 	size_t GetSize() const;
+	size_t GetWriteOffsetGeneric() const;
 	void StartAutoLength();
 	std::span<uint8_t> StopAutoLength();
 	bool IsAutoLengthActive() const { return this->saved_buf != nullptr; }

src/sl/saveload_types.h

@@ -104,25 +104,29 @@ typedef uint32_t VarType;
 /** Type of data saved. */
 enum SaveLoadTypes {
 	SL_VAR = 0,          ///< Save/load a variable.
-	SL_REF         =  1, ///< Save/load a reference.
+	SL_REF,              ///< Save/load a reference.
-	SL_ARR         =  2, ///< Save/load a fixed-size array of #SL_VAR elements.
+	SL_ARR,              ///< Save/load a fixed-size array of #SL_VAR elements.
-	SL_STR         =  3, ///< Save/load a string.
+	SL_STR,              ///< Save/load a string.
-	SL_REFLIST     =  4, ///< Save/load a list of #SL_REF elements.
+	SL_REFLIST,          ///< Save/load a list of #SL_REF elements.
-	SL_RING        =  5, ///< Save/load a ring of #SL_VAR elements.
+	SL_RING,             ///< Save/load a ring of #SL_VAR elements.
-	SL_VEC         =  6, ///< Save/load a vector of #SL_REF elements.
+	SL_VEC,              ///< Save/load a vector of #SL_REF elements.
-	SL_STDSTR      =  7, ///< Save/load a std::string.
+	SL_STDSTR,           ///< Save/load a std::string.
+	SL_PTRRING,          ///< Save/load a ring of #SL_REF elements.
+	SL_VARVEC,           ///< Save/load a primitive type vector.
+
+	SL_STRUCT,           ///< Save/load a struct.
+	SL_STRUCTLIST,       ///< Save/load a list of structs.
 
 	/* non-normal save-load types */
-	SL_WRITEBYTE   =  8,
+	SL_WRITEBYTE,
-	SL_VEH_INCLUDE =  9,
+	SL_VEH_INCLUDE,
-	SL_ST_INCLUDE  = 10,
+	SL_ST_INCLUDE,
-
-	SL_PTRRING     = 13, ///< Save/load a ring of #SL_REF elements.
-	SL_VARVEC      = 14, ///< Save/load a primitive type vector.
 };
 
 typedef uint8_t SaveLoadType; ///< Save/load type. @see SaveLoadTypes
 
+using SaveLoadStructHandlerFactory = std::unique_ptr<struct SaveLoadStructHandler> (*)();
+
 /** SaveLoad type struct. Do NOT use this directly but use the SLE_ macros defined just below! */
 struct SaveLoad {
 	bool global;         ///< should we load a global variable or a non-global one
@@ -132,12 +136,18 @@ struct SaveLoad {
 	SaveLoadVersion version_from; ///< save/load the variable starting from this savegame version
 	SaveLoadVersion version_to;   ///< save/load the variable until this savegame version
 	uint16_t label_tag;  ///< for labelling purposes
+
+	union {
 		/* NOTE: This element either denotes the address of the variable for a global
 		 * variable, or the offset within a struct which is then bound to a variable
 		 * during runtime. Decision on which one to use is controlled by the function
 		 * that is called to save it. address: global=true, offset: global=false */
 		void *address;                                       ///< address of variable OR offset of variable in the struct (max offset is 65536)
+		SaveLoadStructHandlerFactory struct_handler_factory; ///< factory function pointer for SaveLoadStructHandler
+	};
+
 	SlXvFeatureTest ext_feature_test;  ///< extended feature test
+	SaveLoadStructHandler *struct_handler = nullptr;
 };
 
 inline constexpr SaveLoad SLTAG(uint16_t label_tag, SaveLoad save_load)
@@ -175,4 +185,95 @@ inline constexpr NamedSaveLoad NSLT(const char *name, SaveLoad save_load)
 	return { name, save_load, NSLF_TABLE_ONLY };
 }
 
+inline constexpr NamedSaveLoad NSLT_STRUCT(const char *name, SaveLoadStructHandlerFactory factory, SaveLoadVersion from = SL_MIN_VERSION, SaveLoadVersion to = SL_MAX_VERSION, SlXvFeatureTest extver = {})
+{
+	return { name, SaveLoad { true, SL_STRUCT, SLE_FILE_STRUCT, 0, from, to, SLTAG_DEFAULT, { .struct_handler_factory = factory }, extver }, NSLF_TABLE_ONLY };
+}
+
+template <typename T>
+inline constexpr NamedSaveLoad NSLT_STRUCT(const char *name, SaveLoadVersion from = SL_MIN_VERSION, SaveLoadVersion to = SL_MAX_VERSION, SlXvFeatureTest extver = {})
+{
+	SaveLoadStructHandlerFactory factory = []() -> std::unique_ptr<struct SaveLoadStructHandler> {
+		return std::make_unique<T>();
+	};
+	return NSLT_STRUCT(name, factory, from, to, extver);
+}
+
+inline constexpr NamedSaveLoad NSLT_STRUCTLIST(const char *name, SaveLoadStructHandlerFactory factory, SaveLoadVersion from = SL_MIN_VERSION, SaveLoadVersion to = SL_MAX_VERSION, SlXvFeatureTest extver = {})
+{
+	return { name, SaveLoad { true, SL_STRUCTLIST, SLE_FILE_STRUCT, 0, from, to, SLTAG_DEFAULT, { .struct_handler_factory = factory }, extver }, NSLF_TABLE_ONLY };
+}
+
+template <typename T>
+inline constexpr NamedSaveLoad NSLT_STRUCTLIST(const char *name, SaveLoadVersion from = SL_MIN_VERSION, SaveLoadVersion to = SL_MAX_VERSION, SlXvFeatureTest extver = {})
+{
+	SaveLoadStructHandlerFactory factory = []() -> std::unique_ptr<struct SaveLoadStructHandler> {
+		return std::make_unique<T>();
+	};
+	return NSLT_STRUCTLIST(name, factory, from, to, extver);
+}
+
+struct SaveLoadTableData : public std::vector<SaveLoad> {
+	std::vector<std::unique_ptr<struct SaveLoadStructHandler>> struct_handlers;
+};
+
+/** Handler for saving/loading a SL_STRUCT/SL_STRUCTLIST. */
+class SaveLoadStructHandler {
+public:
+	SaveLoadTableData table_data;
+
+	virtual ~SaveLoadStructHandler() = default;
+
+	/**
+	 * Get the (static) description of the fields in the savegame.
+	 */
+	virtual NamedSaveLoadTable GetDescription() const = 0;
+
+	/**
+	 * Get the (current) description of the fields in the savegame.
+	 */
+	SaveLoadTable GetLoadDescription() const { return this->table_data; }
+
+	/**
+	 * Save the object to disk.
+	 * @param object The object to store.
+	 */
+	virtual void Save([[maybe_unused]] void *object) const {}
+
+	/**
+	 * Load the object from disk.
+	 * @param object The object to load.
+	 */
+	virtual void Load([[maybe_unused]] void *object) const {}
+
+	/**
+	 * Similar to load, but used only to validate savegames.
+	 * @param object The object to load.
+	 */
+	virtual void LoadCheck([[maybe_unused]] void *object) const {}
+
+	/**
+	 * A post-load callback to fix #SL_REF integers into pointers.
+	 * @param object The object to fix.
+	 */
+	virtual void FixPointers([[maybe_unused]] void *object) const {}
+};
+
+
+template <class TImpl, class TObject>
+class TypedSaveLoadStructHandler : public SaveLoadStructHandler {
+public:
+	void Save([[maybe_unused]] TObject *object) const {}
+	void Save(void *object) const override { static_cast<const TImpl *>(this)->Save(static_cast<TObject *>(object)); }
+
+	void Load([[maybe_unused]] TObject *object) const {}
+	void Load(void *object) const override { static_cast<const TImpl *>(this)->Load(static_cast<TObject *>(object)); }
+
+	void LoadCheck([[maybe_unused]] TObject *object) const {}
+	void LoadCheck(void *object) const override { static_cast<const TImpl *>(this)->LoadCheck(static_cast<TObject *>(object)); }
+
+	void FixPointers([[maybe_unused]] TObject *object) const {}
+	void FixPointers(void *object) const override { static_cast<const TImpl *>(this)->FixPointers(static_cast<TObject *>(object)); }
+};
+
 #endif /* SL_SAVELOAD_TYPES_H */

src/sl/tracerestrict_sl.cpp

@@ -23,7 +23,7 @@ static const NamedSaveLoad _trace_restrict_mapping_desc[] = {
  */
 static void Load_TRRM()
 {
-	std::vector<SaveLoad> slt = SlTableHeaderOrRiff(_trace_restrict_mapping_desc);
+	SaveLoadTableData slt = SlTableHeaderOrRiff(_trace_restrict_mapping_desc);
 
 	int index;
 	while ((index = SlIterateArray()) != -1) {
@@ -37,7 +37,7 @@ static void Load_TRRM()
  */
 static void Save_TRRM()
 {
-	std::vector<SaveLoad> slt = SlTableHeader(_trace_restrict_mapping_desc);
+	SaveLoadTableData slt = SlTableHeader(_trace_restrict_mapping_desc);
 
 	for (TraceRestrictMapping::iterator iter = _tracerestrictprogram_mapping.begin();
 			iter != _tracerestrictprogram_mapping.end(); ++iter) {
@@ -55,7 +55,7 @@ static const NamedSaveLoad _trace_restrict_program_desc[] = {
  */
 static void Load_TRRP()
 {
-	std::vector<SaveLoad> slt = SlTableHeaderOrRiff(_trace_restrict_program_desc);
+	SaveLoadTableData slt = SlTableHeaderOrRiff(_trace_restrict_program_desc);
 
 	int index;
 	while ((index = SlIterateArray()) != -1) {
@@ -111,7 +111,7 @@ static void Load_TRRP()
  */
 static void Save_TRRP()
 {
-	std::vector<SaveLoad> slt = SlTableHeader(_trace_restrict_program_desc);
+	SaveLoadTableData slt = SlTableHeader(_trace_restrict_program_desc);
 
 	for (TraceRestrictProgram *prog : TraceRestrictProgram::Iterate()) {
 		SlSetArrayIndex(prog->index);
@@ -132,7 +132,7 @@ static const NamedSaveLoad _trace_restrict_slot_desc[] = {
  */
 static void Load_TRRS()
 {
-	std::vector<SaveLoad> slt = SlTableHeaderOrRiff(_trace_restrict_slot_desc);
+	SaveLoadTableData slt = SlTableHeaderOrRiff(_trace_restrict_slot_desc);
 
 	int index;
 	while ((index = SlIterateArray()) != -1) {
@@ -147,7 +147,7 @@ static void Load_TRRS()
  */
 static void Save_TRRS()
 {
-	std::vector<SaveLoad> slt = SlTableHeader(_trace_restrict_slot_desc);
+	SaveLoadTableData slt = SlTableHeader(_trace_restrict_slot_desc);
 
 	for (TraceRestrictSlot *slot : TraceRestrictSlot::Iterate()) {
 		SlSetArrayIndex(slot->index);
@@ -166,7 +166,7 @@ static const NamedSaveLoad _trace_restrict_counter_desc[] = {
  */
 static void Load_TRRC()
 {
-	std::vector<SaveLoad> slt = SlTableHeaderOrRiff(_trace_restrict_counter_desc);
+	SaveLoadTableData slt = SlTableHeaderOrRiff(_trace_restrict_counter_desc);
 
 	int index;
 	while ((index = SlIterateArray()) != -1) {
@@ -180,7 +180,7 @@ static void Load_TRRC()
  */
 static void Save_TRRC()
 {
-	std::vector<SaveLoad> slt = SlTableHeader(_trace_restrict_counter_desc);
+	SaveLoadTableData slt = SlTableHeader(_trace_restrict_counter_desc);
 
 	for (TraceRestrictCounter *ctr : TraceRestrictCounter::Iterate()) {
 		SlSetArrayIndex(ctr->index);

src/sl/train_speed_adaptation.cpp

@@ -25,7 +25,7 @@ static const NamedSaveLoad _train_speed_adaptation_map_desc[] = {
 static void Load_TSAS()
 {
 	const bool table_mode = SlIsTableChunk();
-	std::vector<SaveLoad> slt = SlTableHeaderOrRiff(_train_speed_adaptation_map_desc);
+	SaveLoadTableData slt = SlTableHeaderOrRiff(_train_speed_adaptation_map_desc);
 
 	int index;
 	SignalSpeedType data;
@@ -40,7 +40,7 @@ static void Load_TSAS()
 
 static void Save_TSAS()
 {
-	std::vector<SaveLoad> slt = SlTableHeader(_train_speed_adaptation_map_desc);
+	SaveLoadTableData slt = SlTableHeader(_train_speed_adaptation_map_desc);
 
 	int index = 0;
 	for (auto &it : _signal_speeds) {

src/sl/tunnel_sl.cpp

@@ -25,7 +25,7 @@ static const NamedSaveLoad _tunnel_desc[] = {
 
 static void Save_TUNN()
 {
-	std::vector<SaveLoad> slt = SlTableHeader(_tunnel_desc);
+	SaveLoadTableData slt = SlTableHeader(_tunnel_desc);
 
 	for (Tunnel *tunnel : Tunnel::Iterate()) {
 		SlSetArrayIndex(tunnel->index);
@@ -35,7 +35,7 @@ static void Save_TUNN()
 
 static void Load_TUNN()
 {
-	std::vector<SaveLoad> slt = SlTableHeaderOrRiff(_tunnel_desc);
+	SaveLoadTableData slt = SlTableHeaderOrRiff(_tunnel_desc);
 
 	int index;
 	while ((index = SlIterateArray()) != -1) {