Fix corner case when unknown node ids run out (#16790)

* Fix `NodeDefManager::allocateId()` not terminating after overflow

* MapBlock::correctBlockNodeIds(): Do not ignore errors

Ignoring would lead to information loss, as the local ids were not translated, so they were
replaced by different nodes.
There is `ignore_world_load_errors` to ignore errors.

* Do not advertise without warning for ignore_world_load_errors

src/emerge.cpp

@@ -788,7 +788,8 @@ void *EmergeThread::run()
 			<< "----" << std::endl
 			<< "\"" << e.what() << "\"" << std::endl
 			<< "See debug.txt." << std::endl
-			<< "You can ignore this using [ignore_world_load_errors = true]."
+			<< "This can be ignored using the `ignore_world_load_errors` setting. "
+			<< "But it will also destroy stuff in the affected MapBlocks, do not use."
 			<< std::endl;
 		m_server->setAsyncFatalError(err.str());
 	}

src/mapblock.cpp

@@ -352,12 +352,6 @@ void MapBlock::correctBlockNodeIds(const NameIdMapping *nimap, MapNode *nodes,
 		IGameDef *gamedef)
 {
 	const NodeDefManager *nodedef = gamedef->ndef();
-	// This means the block contains incorrect ids, and we contain
-	// the information to convert those to names.
-	// nodedef contains information to convert our names to globally
-	// correct ids.
-	std::unordered_set<content_t> unnamed_contents;
-	std::unordered_set<std::string> unallocatable_contents;
 
 	// Used to cache local to global id lookup.
 	IdIdMapping &mapping_cache = IdIdMapping::giveClearedThreadLocalInstance();
@@ -372,16 +366,16 @@ void MapBlock::correctBlockNodeIds(const NameIdMapping *nimap, MapNode *nodes,
 
 		std::string name;
 		if (!nimap->getName(local_id, name)) {
-			unnamed_contents.insert(local_id);
+			throw SerializationError("MapBlock::correctBlockNodeIds(): "
-			continue;
+				"Block contains id " + itos(local_id) + " with no name mapping");
 		}
 
 		content_t global_id;
 		if (!nodedef->getId(name, global_id)) {
 			global_id = gamedef->allocateUnknownNodeId(name);
 			if (global_id == CONTENT_IGNORE) {
-				unallocatable_contents.insert(name);
+				throw SerializationError("MapBlock::correctBlockNodeIds(): "
-				continue;
+					"Could not allocate global id for node name \"" + name + "\"");
 			}
 		}
 		nodes[i].setContent(global_id);
@@ -389,17 +383,6 @@ void MapBlock::correctBlockNodeIds(const NameIdMapping *nimap, MapNode *nodes,
 		// Save previous node local_id & global_id result
 		mapping_cache.set(local_id, global_id);
 	}
-
-	for (const content_t c: unnamed_contents) {
-		errorstream << "correctBlockNodeIds(): IGNORING ERROR: "
-				<< "Block contains id " << c
-				<< " with no name mapping" << std::endl;
-	}
-	for (const std::string &node_name: unallocatable_contents) {
-		errorstream << "correctBlockNodeIds(): IGNORING ERROR: "
-				<< "Could not allocate global id for node name \""
-				<< node_name << "\"" << std::endl;
-	}
 }
 
 void MapBlock::serialize(std::ostream &os_compressed, u8 version, bool disk, int compression_level)

src/nodedef.cpp

@@ -794,7 +794,12 @@ content_t NodeDefManager::allocateId()
 		}
 		const ContentFeatures &f = m_content_features[id];
 		if (f.name.empty()) {
-			m_next_id = id + 1;
+			// use saturating add, to avoid overflow of m_next_id, which would
+			// make the loop not terminate (loop cond id >= 0 is always true)
+			if (id < CONTENT_MAX)
+				m_next_id = id + 1;
+			else
+				m_next_id = CONTENT_MAX;
 			return id;
 		}
 	}