Function SlCompatTableHeader

src/saveload/saveload.cpp:2037–2085

* Load a table header in a savegame compatible way. If the savegame was made * before table headers were added, it will fall back to the * SaveLoadCompatTable for the order of fields while loading. * * @note You only have to call this function if the chunk existed as a * non-table type before converting it to a table. New chunks created as * table can call SlTableHeader() directly. * * @pa

 * @return When loading, the ordered SaveLoad array to use; otherwise an empty list.
 */
std::vector<SaveLoad> SlCompatTableHeader(const SaveLoadTable &slt, const SaveLoadCompatTable &slct)
{
	assert(_sl.action == SLA_LOAD || _sl.action == SLA_LOAD_CHECK);
	/* CH_TABLE / CH_SPARSE_TABLE always have a header. */
	if (_sl.block_mode == CH_TABLE || _sl.block_mode == CH_SPARSE_TABLE) return SlTableHeader(slt);

	std::vector<SaveLoad> saveloads;

	/* Build a key lookup mapping based on the available fields. */
	std::map<std::string, std::vector<const SaveLoad *>> key_lookup;
	for (auto &sld : slt) {
		/* All entries should have a name; otherwise the entry should just be removed. */
		assert(!sld.name.empty());

		key_lookup[sld.name].push_back(&sld);
	}

	for (auto &slc : slct) {
		if (slc.name.empty()) {
			/* In old savegames there can be data we no longer care for. We
			 * skip this by simply reading the amount of bytes indicated and
			 * send those to /dev/null. */
			saveloads.emplace_back("", SL_NULL, GetVarFileType(slc.null_type) | SLE_VAR_NULL, slc.null_length, slc.version_from, slc.version_to, nullptr, 0, nullptr);
		} else {
			auto sld_it = key_lookup.find(slc.name);
			/* If this branch triggers, it means that an entry in the
			 * SaveLoadCompat list is not mentioned in the SaveLoad list. Did
			 * you rename a field in one and not in the other? */
			if (sld_it == key_lookup.end()) {
				/* This isn't an assert, as that leaves no information what
				 * field was to blame. This way at least we have breadcrumbs. */
				Debug(sl, 0, "internal error: saveload compatibility field '{}' not found", slc.name);
				SlErrorCorrupt("Internal error with savegame compatibility");
			}
			for (auto &sld : sld_it->second) {
				saveloads.push_back(*sld);
			}
		}
	}

	for (auto &sld : saveloads) {
		if (!SlIsObjectValidInSavegame(sld)) continue;
		if (sld.cmd == SL_STRUCTLIST || sld.cmd == SL_STRUCT) {
			sld.handler->load_description = SlCompatTableHeader(sld.handler->GetDescription(), sld.handler->GetCompatDescription());
		}
	}

	return saveloads;
}

/**
 * Save or Load (a list of) global variables.